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Hypertension is the risk factor of serious cardiovascular diseases, such as ischemic heart disease and atherosclerosis. The aim of the present study was to analyze the development of cardiac tolerance to ischemia in neonatal spontaneously hypertensive rats (SHR) and possible protective effect of ischemic preconditioning (IP) or adaptation to intermittent high-altitude hypoxia (IHAH). For this purpose we used 1- and 10-day-old pups of SHR and their normotensive control Wistar Kyoto rats (WKY). Isolated hearts were perfused in the Langendorff mode with Krebs-Henseleit solution at constant pressure, temperature and rate. Cardiac tolerance to ischemia was expressed as a percentage of baseline values of developed force (DF) after global ischemia. IP was induced by three 3-min periods of global ischemia, each separated by 5-min periods of reperfusion. IHAH was simulated in barochamber (8 h/day, 5000 m) from postnatal day 1 to 10. Cardiac tolerance to ischemia in 1-day-old SHR was higher than in WKY. In both strains tolerance decreased after birth, and the difference disappeared. The high cardiac resistance in 1- and 10-day-old SHR and WKY could not be further increased by both IP and adaptation to IHAH. It may be concluded that hearts from newborn SHR are more tolerant to ischemia/reperfusion injury as compared to age-matched WKY; cardiac resistance decreased in both strains during the first ten days, similarly as in Wistar rats.

Aim: Endothelin-1 (ET-1) plays an important role in the pathogenesis of salt-dependent forms of hypertension in adult rats, but its participation in salt hypertension elicited in immature rats is still unknown. Therefore, we compared ET-1 role in the development or the maintenance of salt hypertension induced in young (4-week-old) or adult (12-week-old) Dahl rats. Methods: The contribution of pressor ET-1 effects to the maintenance of high blood pressure (BP) was studied using acute injection of ETA receptor antagonist ambrisentan (BSF 208075, 1 mg kg 1 iv) to young or adult rats with established salt hypertension. Furthermore, using chronic ambrisentan treatment (30 mg kg 1 day 1 in the drinking fluid during 5 weeks of high salt intake), we investigated the age-dependent involvement of ETA receptors in salt hypertension development in these two age groups. Results: Acute ETA receptor blockade lowered BP in both age groups of salt hypertensive Dahl rats more than in rats fed a low-salt diet (but without any age-dependent difference). Chronic ETA receptor blockade strongly attenuated the development of salt hypertension and cardiac hypertrophy in adult rats, but it had no significant effects on salt hypertension in young animals. Pronounced BP reduction induced in adult salt hypertensive rats by chronic ambrisentan treatment was attributed to attenuated sympathetic BP component, without changes in nitric oxide (NO)-dependent BP regulation. In contrast, chronic ambrisentan treatment of young animals did not modify sympathetic BP component but substantially attenuated NO-dependent vasodilatation. Conclusions: ETA receptor-mediated ET-1 effects play an important role in salt hypertension of adult but not young Dahl rats.

Hypertension is associated with the imbalance of vasoconstrictor and vasodilator systems. Vasodilation is usually evaluated in isolated blood vessels, but except for nitric oxide (NO), relatively little attention is given to the in vivo efficiency of particular vasodilator mechanisms. The aim of our study was to evaluate the contribution of endogenous vasodilator prostanoids, Ca2+-activated K+ channels and NO to blood pressure (BP) maintenance in rats with three different forms of experimental hypertension. Both principal vasopressor systems (the renin–angiotensin system and the sympathetic nervous system) were blocked by captopril and pentolinium in conscious spontaneously hypertensive rats (SHRs), Dahl salt-hypertensive (DS-HS) rats and rats with NO-deficient hypertension, as well as in their normotensive controls. Thereafter, we monitored BP changes in rats subjected to either a sequential or an isolated blockade of prostanoid synthesis by the non-selective cyclooxygenase inhibitor, indomethacin, of Ca2+-activated K+ channels by tetraethylammonium and of NO formation by NG-nitro-L-arginine methyl ester. All three forms of experimental hypertension were characterized by augmented sympathetic vasoconstriction. The vasodilatation exerted by endogenous prostanoids and Ca2+-activated K+ channels was enhanced in all forms of hypertension, almost proportionally to BP elevation. On the contrary, NO-dependent vasodilatation was not enhanced in any form of experimental hypertension, and there was a severe relative NO deficiency in both, SHRs and DS-HS rats. In conclusion, our data suggested that there is a compensatory activation of vasodilator prostanoids and Ca2+-activated K+ channels in rats with experimental hypertension, whereas NO-dependent vasodilatation is not augmented. Thus, the overall activity of vasodilator systems failed to compensate for augmented sympathetic vasoconstriction in hypertensive animals.

Aim: Increased potassium intake attenuates the development of salt-dependent hypertension, but the detailed mechanisms of blood pressure (BP) reduction are still unclear. The aims of our study were (i) to elucidate these mechanisms, (ii) to compare preventive potassium effects in immature and adult animals and (iii) to evaluate the therapeutic effects of dietary potassium supplementation in rats with established salt hypertension. Methods: Young (4-week-old) and adult (24-week-old) female salt-sensitive Dahl rats were fed a high-salt diet (5% NaCl) or a high-salt diet supplemented with 3% KCl for 5 weeks. The participation of vasoconstrictor (renin-angiotensin and sympathetic nervous systems) and vasodilator systems [prostanoids, Ca2+-activated K+ channels, nitric oxide (NO)] was evaluated using a sequential blockade of these systems. Results: Preventive potassium supplementation attenuated the development of severe salt hypertension in young rats, whereas it had no effects on BP in adult rats with moderate hypertension. Enhanced sympathetic vasoconstriction was responsible for salt hypertension in young rats and its attenuation for potassium-induced BP reduction. Conversely, neither salt hypertension nor its potassium-induced attenuation were associated with significant changes of the vasodilator systems studied. The relative deficiency of vasodilator action of NO and Ca2+-activated K+ channels in salt hypertensive Dahl rats was not improved by potassium supplementation. Conclusions: The attenuation of enhanced sympathetic vasoconstriction is the principal mechanism of antihypertensive action exerted by preventive potassium supplementation in immature Dahl rats. Dietary potassium supplementation has no preventive effects on BP in adult salt-loaded animals or no therapeutic effects on established salt hypertension in young rats.

The mechanisms responsible for the antihypertensive effect of melatonin are not completely understood. To elucidate the possible role of the nitric oxide (NO) pathway in the hemodynamic actions of melatonin, the effects of this indolamine on vascular function during hypertension induced by the NO-synthase (NOS) inhibitor, N(omega)-nitro-L-arginine-methyl ester (L-NAME) were investigated. Four groups of male adult Wistar rats were employed: control, L-NAME (40 mg/kg), melatonin (10 mg/kg) and L-NAME + melatonin for 5 wks. Systolic and diastolic blood pressure were measured invasively in the carotid artery. Conjugated dienes concentration (an oxidative load marker), NOS RNA expression and its activity and RNA expression of cyclooxygenase-(COX)-1 and COX-2 were determined in the aorta. Acetylcholine-induced responses and their NO-mediated component were evaluated in femoral and mesenteric artery. Moreover, endothelium-derived constricting factor (EDCF)-dependent vasoconstriction and inner diameter were determined in the femoral artery. Chronic L-NAME treatment induced hypertension, elevated the oxidative load and inhibited NOS activity. Moreover, impaired NO-dependent relaxation, augmented EDCF-constriction, increased COX-2 expression and reduced arterial inner diameter were observed. Melatonin added to L-NAME treatment completely prevented elevation of the oxidative load in the aorta. However, melatonin was not able to prevent NOS activity decline, elevation of COX-2 expression or the impairment of vascular responses (except moderate improvement in relaxation of small mesenteric arteries) and it exerted only slight antihypertensive effect. In conclusion, in addition to the reduction of the oxidative load, the restoration of the NO pathway seems to play an important role in the antihypertensive effect of melatonin.

Neurogenic pulmonary edema (NPE) is an acute life-threatening complication following an injury of the spinal cord or brain, which is associated with sympathetic hyperactivity. The role of nitric oxide (NO) in NPE development in rats subjected to balloon compression of the spinal cord has not yet been examined. We, therefore, pretreated Wistar rats with the NO synthase inhibitor NG-nitro-l-arginine methyl ester (l-NAME) either acutely (just before the injury) or chronically (for 4 wk prior to the injury). Acute (but not chronic) l-NAME administration enhanced NPE severity in rats anesthetized with 1.5% isoflurane, leading to the death of 83% of the animals within 10 min after injury. Pretreatment with either the ganglionic blocker pentolinium (to reduce blood pressure rise) or the muscarinic receptor blocker atropine (to lessen heart rate decrease) prevented or attenuated NPE development in these rats. We did not observe any therapeutic effects of atropine administered 2 min after spinal cord compression. Our data indicate that NPE development is dependent upon a marked decrease of heart rate under the conditions of high blood pressure elicited by the activation of the sympathetic nervous system. These hemodynamic alterations are especially pronounced in rats subjected to acute NO synthase inhibition. In conclusion, nitric oxide has a partial protective effect on NPE development because it attenuates sympathetic vasoconstriction and consequent baroreflex-induced bradycardia following spinal cord injury.

The development of neurogenic pulmonary edema (NPE) can be elicited by an immediate epidural balloon compression of the thoracic spinal cord. To evaluate whether a slower balloon inflation could prevent NPE development, we examined the extent of NPE in animals lesioned with a rapid (5 microl - 5 microl - 5 microl) or slow rate (3 microl - 2 microl - 2 microl - 2 microl - 2 microl - 2 microl - 2 microl) of balloon inflation. These groups were compared with the NPE model (immediate inflation to 15 microl) and with healthy controls. Slow balloon inflation prevented NPE development, whereas the pulmonary index and histology revealed a massive pulmonary edema in the group with a rapid rate of balloon inflation. Pulmonary edema was preceded by a considerable decrease in heart rate during the inflation procedure. Moreover, rapid inflation of balloon in spinal channel to either 5 microl or 10 microl did not cause NPE. Thus, a slow rate of balloon inflation in the thoracic epidural space prevents the development of neurogenic pulmonary edema, most likely due to the better adaptation of the organism to acute circulatory changes (rapid elevation of systemic blood pressure accompanied by profound heart rate reduction) during the longer balloon inflation period. It should be noted that spinal cord transection at the same level did not cause neurogenic pulmonary edema.

Prague hypertriglyceridemic (HTG) rats represent a suitable model of metabolic syndrome. We have established the set of F(2) hybrids derived from HTG and Lewis progenitors to investigate the relationship between respective polymorphism(s) of Igf2 gene and blood pressure (BP) or other cardiovascular phenotypes. HTG rats had elevated systolic BP and plasma triglycerides but lower plasma cholesterol compared to Lewis rats of both genders. In males, there was higher mean arterial pressure, diastolic BP and relative heart weight in HTG than in Lewis rats. The results obtained in the total population of F(2) hybrids indicated strong segregation of Igf2 genotype with plasma triglycerides. There was no segregation of Igf2 genotype with any BP component except BP changes occurring after the blockade of either renin-angiotensin system (RAS) or NO synthase. When F(2) population was analyzed according to gender, male F(2) progeny homozygous for HTG Igf2 allele had significantly higher plasma triglycerides and greater BP changes after NO synthase blockade than those homozygous for Lewis allele. On the contrary, male F(2) progeny homozygous for HTG Igf2 allele had significantly lower plasma cholesterol and smaller BP changes after RAS blockade. PCR analysis of Igf2 gene by using of microsatelite D1Mgh22 has shown polymorphism between HTG and Lewis rats. Sequence analysis of cDNA revealed insertion of 14 nucleotides in HTG gene. In conclusion, polymorphism in Igf2 gene may be responsible for differences in lipid metabolism between HTG and Lewis rats. It remains to determine how these abnormalities could be involved in BP regulation by particular vasoactive systems.

Neurogenic pulmonary edema is a life-threatening complication, known for almost 100 years, but its etiopathogenesis is still not completely understood. This review summarizes current knowledge about the etiology and pathophysiology of neurogenic pulmonary edema. The roles of systemic sympathetic discharge, central nervous system trigger zones, intracranial pressure, inflammation and anesthesia in the etiopathogenesis of neurogenic pulmonary edema are considered in detail. The management of the patient and experimental models of neurogenic pulmonary edema are also discussed.

Recombinant inbred (RI) strains (Prague HXB/BXH set) represent a unique model that allows for permanent summation of genetic and physiological information as well as the study of age-dependent changes in phenotypes and/or gene regulation. This study compared blood pressure (BP) measured in adult animals of RI strains by radiotelemetry with BP values obtained in conscious rats of comparable age subjected to short-term carotid catheterization or with those obtained by direct carotid puncture under ether anesthesia (almost 20 years ago). After radiotelemetry recording, the contribution of major vasoactive systems to BP maintenance was studied by consecutive inhibition of the renin-angiotensin system (RAS), sympathetic nervous system (SNS), and nitric oxide synthase. We found highly significant interrelationships among baseline BP values obtained by radiotelemetry, carotid catheterization, or carotid puncture. This indicates considerable stability of RI strains over the course of their long existence, and confirms the reliability of BP values used for genetic studies performed in the past. Subsequent analysis of vasoactive system participation revealed the importance of SNS for the maintenance of BP, as determined by either radiotelemetry or catheterization. The BP of catheterized rats also correlated closely with acute captopril-induced BP changes, but this was not the case for rats measured by radiotelemetry. NO-dependent vasodilatation matched the BP effects of SNS and RAS in both measuring conditions. Residual BP (recorded at sodium nitroprusside-induced dilatation of resistance vessels) was also responsible for a significant portion of the BP variation in RI strains. Our study confirms the validity of RI strains for the further genetic and physiological research of hypertension.

Neurogenic pulmonary edema is an acute life-threatening complication following central nervous system injury. The exact pathogenic mechanism leading to its development is still unclear. We introduce a new hypothesis that high levels of anesthesia might protect the organism against the development of neurogenic pulmonary edema due to a more pronounced inhibition of the hypothalamic, brainstem and spinal vasoactive sympathetic centers. On the basis of a more pronounced neuronal inhibition of the vasoactive centers, a severe sympathetic discharge does not occur and neurogenic pulmonary edema does not develop. In contrast, an insufficient anesthesia level is not able to inhibit the sympathetic nervous system during an injury of the central nervous system and thus neurogenic pulmonary edema develops. During experiments with central nervous system injury, low-anesthesia-induced neurogenic pulmonary edema might negatively influence the overall recovery of the animal. More importantly, during a neurosurgical intervention, insufficient anesthesia might similarly lead to neurogenic pulmonary edema development in operated patients. Our hypothesis indicates the necessity of precisely monitoring of the level anesthesia during experimental manipulations of the central nervous system in animals or neurosurgical interventions in humans.

Aim: The relationship between increased sympathetic tone and enhanced activity of L-type voltage-dependent Ca2+ channels (L-VDCC) in spontaneously hypertensive rats (SHR) was studied using in vivo and in vitro approaches. Methods: The effects of acute L-VDCC blockade on sympathetic vasoconstriction or blood pressure (BP) and the contribution of calcium influx to norepinephrine (NE)-induced arterial contraction were investigated in 10-week-old SHR and in age-matched SHR made normotensive by chronic captopril treatment from weaning. Results: Blood pressure fall occurring after acute ganglionic or L-VDCC blockade was enhanced in SHR. Ganglionic blockade eliminated strain differences in BP response to acute L-VDCC blockade and vice versa, suggesting that enhanced contribution of L-VDCC is responsible for augmented sympathetic vasoconstriction in SHR. Both phasic (dependent on internal calcium stores) and tonic (dependent on calcium influx) contractions to NE were augmented in SHR femoral arteries in vitro. Nifedipine attenuated only tonic contractions but to a larger extent in SHR than in WKY arteries. Nifedipine effect was greater after endothelium removal, which augmented tonic but not phasic contractions after NE. Chronic captopril treatment of SHR prevented hypertension development by suppression of their sympathetic vasoconstriction including its nifedipine-sensitive component, but failed to influence enhanced NE-induced arterial contractions or increased relaxation to nifedipine in vitro. Conclusion: The contribution of nifedipine-sensitive component to noradrenergic vasoconstriction is enhanced during excessive NE stimulation (increased sympathetic tone of SHR in vivo or supramaximal NE stimulation in vitro). It seems that captopril-induced reduction of central sympathetic tone is able to normalize augmented nifedipine-sensitive vasoconstriction in SHR.

Several non-aromatic substituted oxime derivatives (formamidoxime, acetaldoxime, acetone oxime, acetohydroxamic acid, formaldoxime) function as vasorelaxant NO donors when added to precontracted aortic rings in vitro. This study was aimed to evaluate whether these substances posses vasodilator properties under in vivo conditions. We studied blood pressure changes elicited by administration of these compounds to conscious chronically catheterized Wistar rats in which endogenous NO synthesis was acutely inhibited by Nω-nitro- l -arginine methyl ester (L-NAME) pretreatment (30 mg/kg i.v.). Three of the tested substances (formaldoxime, acetohydroxamic acid and formamidoxime) induced pronounced dose-dependent blood pressure reduction which was further augmented when baroreflex operation was interrupted by ganglionic blockade (5 mg/kg pentolinium). Pretreatment of rats with methylene blue (soluble guanylate cyclase inhibitor) was used to estimate the contribution of NO to observed blood pressure lowering effects of the above compounds. Nitric oxide seems to be responsible for the entire formaldoxime-induced blood pressure decrease and for a considerable part of blood pressure changes elicited by formamidoxime. On the contrary, we did not find a significant NO contribution to blood pressure reduction caused by acetohydroxamic acid. In conclusion, our study confirmed in vivo vasodilator effects of three above mentioned compounds which were earlier demonstrated to induce in vitro vasorelaxation. It indicated a variable contribution of nitric oxide to blood pressure changes elicited by particular compounds. Substances with hydrophilic character (formamidoxime, acetohydroxamic acid, formaldoxime) were effective, whereas less hydrophilic substance (acetaldoxime) or slightly hydrophobic one (acetone oxime) were ineffective.

Anesthetics can either promote or inhibit the development of neurogenic pulmonary edema (NPE) after central nervous system (CNS) injury. The influence of isoflurane was examined in male Wistar rats using 1.5%, 2%, 2.5%, 3%, 4%, or 5% isoflurane in air. Epidural balloon compression of the thoracic spinal cord was performed. The development of NPE was examined in vivo and on histologic sections of lung tissue. Animals anesthetized with 1.5% or 3% isoflurane were behaviorally monitored using the BBB and plantar tests for 7 weeks post-injury. The spinal cord was examined using MRI and morphometry of the spared white and gray matter. All animals from the 1.5% and 2% groups developed NPE. Almost 42% of the animals in the 1.5% group died of severe pulmonary hemorrhage and suffocation; x-rays, the pulmonary index, and the histological picture revealed a massive NPE. More than 71% of the animals from the 2.5% and 3% groups did not develop any signs of NPE. Blood pressure after spinal cord compression rose more in the 1.5% group than in the 3% one. In the 1.5% group, the sympathetic ganglionic blockade prevented the neurogenic pulmonary edema development. Animals from the 3% group recovered behaviorally more rapidly than did the animals from the 1.5% group; morphometry and MRI of the lesions showed no differences. Thus, low levels of isoflurane anesthesia promote NPE in rats with a compressed spinal cord and significantly complicates their recovery. The optimal concentration of anesthesia for performing a spinal cord compression lesion is 2.5-3% isoflurane in air.

1. The present study deals with the effect of maturation on the kinetic properties of renal Na(+)/K(+)-ATPase and its susceptibility to nitric oxide (NO)-deficient hypertension induced by the NO synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME). 2. Immature (4-week-old) and adult (12-week-old) male Wistar rats were administered L-NAME (40 mg/kg per day) in their drinking water for 4 weeks. 3. The properties of the ATP- and Na(+)-binding sites of Na(+)/K(+)-ATPase were investigated by activation of the enzyme with increasing concentrations of the energy substrate ATP and/or cofactor Na(+). Unchanged values of K(m) suggest that energy utilization by the enzyme in the kidney of control rats remains unaffected during maturation. Conversely, the decrease in K(Na) values (the concentration of Na(+) necessary to achieve half-maximal reaction velocity) indicates improved affinity for Na(+) in the older group of control rats. 4. Application of L-NAME to all young animals had no significant effect on the functional properties of Na(+)/K(+)-ATPase. 5. In adult animals, the V(max) values remained unchanged after treatment with L-NAME, but the affinities of the ATP- and Na(+)-binding sites were decreased, as indicated by significant increase in K(m) and K(Na) values. 6. Maturation of control rats was accompanied by an increase in the Na(+) affinity of renal Na(+)/K(+)-ATPase without affecting ATP utilization. However, maturation increased the susceptibility of renal Na(+)/K(+)-ATPase to the harmful effects of L-NAME.

The incidence of metabolic syndrome increases in the developed countries, therefore biomedical research is focused on the understanding of its etiology. The study of exact mechanisms is very complicated because both genetic and environmental factors contribute to this complex disease. The ability of environmental factors to promote phenotype changes by epigenetic DNA modifications (i.e. DNA methylation, histone modifications) was demonstrated to play an important role in the development and predisposition to particular symptoms of metabolic syndrome. There is no doubt that the early life, such as the fetal and perinatal periods, is critical for metabolic syndrome development and therefore critical for prevention of this disease. Moreover, these changes are visible not only in individuals exposed to environmental factors but also in the subsequent progeny for multiple generations and this phenomenon is called transgenerational inheritance. The knowledge of molecular mechanisms, by which early minor environmental stimuli modify the expression of genetic information, might be the desired key for the understanding of mechanisms leading to the change of phenotype in adulthood. This review provides a short overview of metabolic syndrome epigenetics.

Altered calcium sensitization (mediated by RhoA/Rho-kinase pathway) and enhanced calcium entry through L-type voltage-dependent calcium channels (L-VDCCs) participate in blood pressure (BP) maintenance of adult spontaneously hypertensive rats (SHRs). This study aimed to evaluate ontogenetic changes of these two pathways in BP control of SHR and Wistar-Kyoto (WKY) aged 3, 5, 7, 13, 26 and 42 weeks.BP response to acute administration of Rho-kinase inhibitor fasudil or L-VDCC blocker nifedipine and the expression of particular components of RhoA/Rho-kinase pathway were determined in young and adult animals.Fasudil-induced BP reduction was attenuated in young SHR compared with WKY, but was enhanced in adult SHR. In contrast, BP response to nifedipine was similar in 3-week-old SHR and WKY and it was augmented with age in SHR but not in WKY. Consequently, the ratio between fasudil-induced and nifedipine-induced BP changes was lower in all age groups of SHR compared with WKY. Fasudil effects on contractility of isolated arteries were attenuated in young but not in adult SHR. mRNA expression of selected Rho-GEFs (Arhgef1, Arhgef11 and Arhgef12) was decreased only in adult SHR, whereas p63RhoGEF and CPI-17 expression was reduced in both age groups of SHR. Active RhoA and phosphorylated CPI-17 were increased in adult but not in young SHR.The importance of RhoA/Rho-kinase pathway for BP/vascular tone control is attenuated in SHR from prehypertensive stages. Enhanced RhoA activation and/or CPI-17 phosphorylation might be counteracted by reduced expression of upstream activators of Rho-kinase (Rho-GEFs) together with lower expression of CPI-17 (in downstream cascade of Rho-kinase).

Aims Chronic endothelin receptor A (ET A ) blockade lowered blood pressure (BP) by decreasing angiotensin-dependent vasoconstriction and attenuating calcium influx. We tested whether the addition of ET A blockade to renin–angiotensin system (RAS) blockade would have further effects on the principal vasoactive systems contributing to BP maintenance in Ren-2 transgenic rats (TGR). Methods Four-week-old TGR rats were fed with normal-salt diet and given either different renin–angiotensin system (RAS) blockers [angiotensin receptor blocker losartan, angiotensin converting enzyme inhibitor captopril, direct renin inhibitor aliskiren], or ET A blocker (atrasentan) alone, or a combination of atrasentan with RAS blockers for 4 weeks. At the end of the study, basal BP and acute BP responses to sequential blockade of renin–angiotensin (RAS), sympathetic nervous (SNS), and nitric oxide (NO) systems were determined in conscious rats. Thereafter, BP responses to acute inhibition of nifedipine-sensitive calcium influx through voltage-dependent calcium channels (L-VDCC) were measured. Key findings All RAS blockers similarly decreased BP to normotension, their effects being mediated through substantially attenuated RAS-dependent and moderately decreased SNS-dependent vasoconstriction. Atrasentan alone partially lowered BP, while BP was normalized by combination of atrasentan with either RAS blocker. In combination therapies, BP lowering effects resulted from the attenuation of both RAS- and SNS-dependent vasoconstriction. Moreover, atrasentan-treated groups had substantially reduced NO-dependent vasodilation and significantly decreased calcium influx through L-VDCC. Conclusions Although the BP-lowering effect of combined ET A and RAS blockades in TGR is predominantly dependent on the effects exerted by RAS blockade, further effects are attributable to decreased calcium influx due to chronic ET A blockade .

Genetic studies in humans and rodent models should help to identify altered genes important in the development of cardiovascular diseases, such as hypertension. Despite the considerable research effort, it is still difficult to identify all of the genes involved in altered blood pressure regulation thereby leading to essential hypertension. We should keep in mind that genetic hypertension and other cardiovascular diseases might develop as a consequence of early errors in well-co-ordinated systems regulating cardiovascular homoeostasis. If these early abnormalities in the ontogenetic cascade of expression of genetic information occur in critical periods of development (developmental windows), they can adversely modify subsequent development of the cardiovascular system. The consideration that hypertension and/or other cardiovascular diseases are late consequences of abnormal ontogeny of the cardiovascular system could explain why so many complex interactions among genes and environmental factors play such a significant role in the pathogenesis of these diseases. The detailed description and precise time resolution of major developmental events occurring during particular stages of ontogeny in healthy individuals (including advanced knowledge of gene expression) could facilitate the detection of abnormalities crucial for the development of cardiovascular alterations characteristic of the respective diseases. Transient gene switch-on or switch-off in specific developmental windows might be a useful approach for in vivo modelling of pathological processes. This should help to elucidate the mechanisms underlying cardiovascular diseases (including hypertension) and to develop strategies to prevent the development of such diseases.

Increased blood pressure (BP) in genetic hypertension is usually caused by high activity of sympathetic nervous system (SNS) which is enhanced by central angiotensin II but lowered by central nitric oxide (NO). We have therefore evaluated NO synthase (NOS) activity as well as neuronal NOS (nNOS), inducible NOS (iNOS) and endothelial NOS (eNOS) protein expression in brainstem and midbrain of adult spontaneously hypertensive rats (SHR) characterized by enhanced sympathetic vasoconstriction. We also studied possible participation of brain NO in antihypertensive effects of chronic captopril treatment of adult SHR. NOS activity was increased in midbrain of SHR compared to Wistar-Kyoto (WKY) rats. This could be ascribed to enhanced iNOS expression, whereas nNOS expression was unchanged and eNOS expression was reduced in this brain region. In contrast, no significant changes of NOS activity were found in brainstem of SHR in which nNOS and iNOS expression was unchanged, but eNOS expression was increased. Chronic captopril administration lowered BP of adult SHR mainly by attenuation of sympathetic tone, whereas the reduction of angiotensin II-dependent vasoconstriction and the decrease of residual BP (amelioration of structural remodeling of resistance vessels) were less important. This treatment did not affect significantly either NOS activity or expression of any NOS isoform in the two brain regions. Our data do not support the hypothesis that altered brain NO formation contributes to sympathetic hyperactivity and high BP of adult SHR with established hypertension.

Distinct changes of membrane lipid content could contribute to the abnormalities of ion transport that take part in the development of salt hypertension in Dahl rats. The relationships between lipid content and particular ion transport systems were studied in red blood cells (RBC) of Dahl rats kept on low- and high-salt diets for 5 weeks since weaning. Dahl salt-sensitive (SS/Jr) rats on high-salt diet had increased blood pressure, levels of plasma triacylglycerols and total plasma cholesterol compared to salt-resistant (SR/Jr) rats. Furthermore, RBC of SS/Jr rats differed from SR/Jr ones by increased content of total membrane phospholipids, but membrane cholesterol was not changed significantly. SS/Jr rats had higher RBC intracellular Na + (Na i + ) content and enhanced bumetanide-sensitive Rb + uptake. RBC membrane content of cholesterol and phospholipids correlated positively with RBC Na i + content, with the activity of Na + –K + pump and Na + –K + –2Cl − cotransport and also with Rb + leak. The content of phosphatidylserines plus phosphatidylinositols was positively associated with RBC Na i + content, with the activity of Na + –K + pump and Na + –K + –2Cl − cotransport and with Rb + leak. The content of sphingomyelins was positively related to Na + –K + –2Cl − cotransport activity and negatively to ouabain-sensitive Rb + –K + exchange. We can conclude that observed relationships between ion transport and the membrane content of cholesterol and/or sphingomyelins, which are known to regulate membrane fluidity, might participate in the pathogenesis of salt hypertension in Dahl rats.

The aim of our study was to evaluate whether the blood pressure (BP) response to chronic inhibition of NO synthase (NOS) is exaggerated in young rats, which were reported to develop a more pronounced salt hypertension than the adult ones. The enhanced BP rise in immature rats subjected to excess salt intake might be due either to a generally increased reactivity in immature organisms to these stimuli or to a greater impairment of NO bioavailability that accompanies the development of salt hypertension. To determine between the two alternatives, we have compared the hypertensive response and the extent of NOS inhibition in immature (4-week-old) and adult (12-week-old) male Wistar rats which were treated with NG-nitro-L-arginine methyl ester (L-NAME, 40 mg/kg of body mass per day) for 4 weeks. BP and NOS activity in the aorta, left ventricle and kidney were determined at the end of the experiment. It should be noted that chronic L-NAME treatment caused a similar degree of NOS inhibition in both age groups (irrespective of tissue examined). There was no significant difference in BP elevation between young and adult animals chronically treated with L-NAME. A strong negative correlation between NOS activity and BP level was observed in separate groups of normotensive controls and L-NAME hypertensive rats. Thus the BP of both normotensive and hypertensive animals seems to be inversely proportional to the production of NO. It can be concluded that there was the same BP rise in both age groups of L-NAME-treated rats in which a similar degree of NOS inhibition was disclosed. This suggests that the altered NO bioavailability (but not the generally exaggerated reactivity to hypertensive stimuli) is the cause of exaggerated hypertensive response observed in immature rats exposed to excess salt intake.

The aim of our study was to search for abnormalities of sodium and potassium transport in erythrocytes of male Wistar rats subjected to chronic L-NAME treatment (40 mg/kg/day) for 4 weeks either from weaning (4-week-old) or in adulthood (12-week-old). Sodium content, Na + ,K + -pump and Na + ,K + -cotransport activity, cation leaks as well as membrane cholesterol and phospholipid contents were determined in fresh erythrocytes. Chronic inhibition of NO synthase elicited similar blood pressure rise in both age groups which did not differ in the degree of NO synthase inhibition. No significant ion transport abnormalities were disclosed in erythrocytes of young NO-deficient rats, whereas erythrocyte Na + content, outward Na + ,K + -cotransport and inward Na + leak were significantly reduced in adult hypertensive animals compared to age-matched controls. It should be noted that the erythrocytes of adult control rats were characterized by higher activity of Na + ,K + -pump and Na + ,K + -cotransport, increased Na + and Rb + leaks and elevated membrane cholesterol content compared to those of young normotensive controls. Increased Na + leak and elevated membrane cholesterol content but reduced membrane phosholipid content were revealed in erythrocytes of adult hypertensive rats when compared to young hypertensive rats. It can be concluded that young and adult Wistar rats did not differ in the extent of NO synthase inhibition and blood pressure rise elicited by chronic L-NAME treatment. Our results exclude the important participation of classical sodium transport abnormalities in the pathogenesis of this NO-deficient form of experimental hypertension.

Acute pharmacogenetic analysis was carried out in an intercross F2 population derived from Prague hypertensive-hypertriglyceridemic and Lewis rats. Quantitative trait loci (QTL) mapping was performed for baseline blood pressure (BP) and for BP after blockade of the renin-angiotensin system by losartan, of the sympathetic nervous system (SNS) by pentolinium, and of the nitric oxide system by N(G)-nitro- L-arginine methyl ester. Two significant loci for baseline BP were found on chromosome (Chr) 3 (logarithm of likelihood, LOD, 3.8) and Chr 5 (LOD 3.6), and one suggestive locus on Chr 1 (LOD 2.7). The QTL on Chr 3 persisted after treatment with the three agents while the QTL on Chr 5 and Chr 1 disappeared after pentolinium administration. This suggests independence of the locus on Chr 3 from each acute BP regulatory system examined, whereas the loci on Chr 5 and Chr 1 appeared to be controlled mainly by the SNS. Although not apparent at baseline, a significant locus appeared on Chr 8 (LOD 7.0) after blockade of the SNS, and NO system blockade led to the appearance of a new QTL on Chr 1 (LOD 3.6), indicating the contribution of the inhibited systems to these loci. Pharmacogenetic dissection of the BP trait is a powerful tool to unravel the underlying physiological mechanisms of QTL affecting baseline BP and to identify specific QTL for the response to drugs. This pharmocogenetic approach enabled us to determine the main causative acute BP regulatory systems and should lead to better selection of suitable antihypertensive drugs for individual patients.

The possible association of salt hypertension and altered lipid metabolism with abnormalities of particular systems transporting sodium and potassium has been studied in erythrocytes of Dahl rats and their F2 hybrids fed a high-salt diet since weaning. Our attention was paid to the Na+-K+ pump, Na+-K+ cotransport and especially to passive membrane permeability for Na+ and Rb+ (Na+ and Rb+ leak), because the Na+ leak was found to be dependent on the genotype, age and salt intake of Dahl rats, whereas the Rb+ leak was suggested to be a potential marker of salt sensitivity in Dahl and Sabra rats. Young male Dahl salt-sensitive (SS/Jr) and salt-resistant (SR/Jr) rats kept on a low-salt (0.3% NaCl) or high-salt diet (8% NaCl) were used for the progenitor study. The subsequent genetic study was based on 135 young male SS/Jr×SR/Jr F2 hybrids fed a high-salt diet since weaning. Ouabain (5 mmol/l) and bumetanide (10μmol/l) were used to distinguish the contribution of the Na+-K+ pump, Na+-K+ cotransport and passive membrane permeability to measured net Na+ fluxes and unidirectional Rb+ (K+) movements. Compared to normotensive SR/Jr animals, salt-loaded SS/Jr rats had higher blood pressure (BP), elevated erythrocyte Na+ content, and increased Na+ and Rb+ leaks together with enhanced Na+ and Rb+ transport mediated by the Na+-K+ pump and Na+-K+ cotransport system. Salt hypertensive Dahl rats were also characterized by elevated plasma levels of total cholesterol and triglycerides, which were positively associated with BP of F2 hybrids (r =0.27 and 0.24, p

OBJECTIVE We have demonstrated earlier that the nitric oxide (NO) system is not able to counterbalance effectively the hyperactivity of the sympathetic nervous system (SNS) in salt hypertension of young Dahl rats in which augmented superoxide anion formation lowers NO bioavailability. The aim of the present study was to determine whether SNS hyperactivity and/or relative NO deficiency are also present in salt hypertension elicited in adult Dahl rats, and whether they are associated with blood pressure (BP) in the F2 population of Dahl rats. DESIGN AND METHODS The contribution of major vasoactive systems [renin-angiotensin system (RAS), SNS and NO] and superoxide anions to BP maintenance was studied in SS/Jr rats in which salt hypertension was induced either in adulthood or in youth (8% NaCl diet from the age of 12 or 4 weeks). The contribution of particular vasoactive systems was also investigated in 122 young salt-loaded F2hybrids [derived from salt-sensitive (SS/Jr) and salt-resistant (SR/Jr) Dahl rats] which were fed a high-salt diet (8% NaCl) for 6 weeks after weaning. Mean arterial pressure (MAP) was measured in conscious animals subjected to acute consecutive blockade of RAS (captopril 10 mg/kg i.v.), SNS (pentolinium 5 mg/kg i.v.) and NO synthase (l-NAME 30 mg/kg i.v.). RESULTS Dahl rats with salt hypertension induced in adulthood were also characterized by enhanced pentolinium-induced BP fall (DeltaMAPpento), but their residual BP (recorded after the blockade of both RAS and SNS) was unaltered, in contrast to its elevation seen in young salt-hypertensive rats. The BP rise after NO synthase inhibition by l-NAME (DeltaMAPL-NAME), which was substantially greater in adult than in young hypertensive rats, was not enhanced by superoxide scavenging with tempol in adult hypertensive animals, in which this drug elicited a moderate BP reduction only. Basal MAP of young salt-loaded F2 hybrids was positively associated not only with DeltaMAPpento (P < 0.0001) and residual BP (P < 0.001) but also with DeltaMAPL-NAME (P < 0.001). The slope of the relationship between basal BP and pentolinium-induced BP changes was steeper than that between basal BP and BP changes elicited by l-NAME. The positive correlation of basal BP with DeltaMAPpento/DeltaMAPL-NAME ratio (P < 0.01) indicates that an altered balance between sympathetic vasoconstriction and NO-dependent vasodilation was associated with high blood pressure, even in the F2 population of Dahl rats. CONCLUSIONS A comparison of young and adult salt-hypertensive Dahl rats stressed the importance of increased residual BP and relative NO deficiency for the severity of hypertension, because these two alterations were absent in a less-pronounced form of salt hypertension elicited in adulthood. The findings obtained in our young salt-loaded F2 population also confirm the major importance of both sympathetic hyperactivity and relative NO deficiency for the maintenance of salt hypertension in Dahl rats.

Neurogenic pulmonary edema (NPE) is a life-threatening complication of central nervous system (CNS) injuries. This review summarizes current knowledge about NPE etiology and pathophysiology with an emphasis on its experimental models, including our spinal cord compression model. NPE may develop as a result of activation of specific CNS trigger zones located in the brainstem, leading to a rapid sympathetic discharge, rise in systemic blood pressure, baroreflex-induced bradycardia, and enhanced venous return resulting in pulmonary vascular congestion characterized by interstitial edema, intra-alveolar accumulation of transudate, and intra-alveolar hemorrhages. The potential etiological role of neurotransmitter changes in NPE trigger zones leading to enhanced sympathetic nerve activity is discussed. Degree of anesthesia is a crucial determinant for the extent of NPE development in experimental models because of its influence on sympathetic nervous system activity. Sympathetic hyperactivity is based on the major activation of either ascending spinal pathways by spinal cord injury or NPE trigger zones by increased intracranial pressure. Attenuation of sympathetic nerve activity or abolition of reflex bradycardia completely prevent NPE development in our experimental model. Suggestions for future research into NPE pathogenesis as well as therapeutic potential of particular drugs and interventions are discussed.

BACKGROUND Our previous experiments demonstrated that selective endothelin A (ETA) receptor blockade had antihypertensive effects in Ren-2 transgenic rats (TGRs), but the mechanisms responsible for this change of blood pressure (BP) have not been explored yet. METHOD Four-week-old male heterozygous TGRs and their normotensive controls--Hannover Sprague-Dawley (HanSD) rats--were fed high-salt diet (2% NaCl) and were treated with selective ETA receptor blocker atrasentan (5 mg/kg per day) for 8 weeks. At the end of the study, the contribution of principle vasoactive systems was evaluated by the sequential blockade of the renin-angiotensin system (captopril), sympathetic nervous system (pentolinium) and nitric oxide synthase [N-nitro-L-arginine methyl ester (L-NAME)]. The role of calcium influx through L-type voltage-dependent calcium channels in BP maintenance was evaluated using nifedipine. In a separate group of animals, the efficiency of distinct vasodilator systems--prostanoids (blocked by nonselective cyclooxygenase inhibitor indomethacin) and Ca-activated K channels (inhibited by tetraethylammonium)--was also analyzed. RESULTS Atrasentan attenuated the development of hypertension in heterozygous TGRs, but had no effects in Hannover Sprague-Dawley rats. Moreover, atrasentan moderately attenuated renin-angiotensin system-dependent vasoconstriction, whereas it had no effect on sympathetic vasoconstriction. The nifedipine-sensitive BP component was markedly decreased by atrasentan treatment. In contrast, vasodilatation mediated by nitric oxide, endogenous prostanoids or Ca-activated K channels was reduced in atrasentan-treated TGRs, indicating the absence of compensatory augmentation of endothelin B receptor-mediated vasodilation in these animals. CONCLUSION BP-lowering effect of chronic atrasentan treatment in TGRs was mainly caused by reduced Ca influx through L-type voltage-dependent calcium channels due to missing ETA receptor-dependent vasoconstriction and attenuated angiotensin II-dependent vasoconstriction.

Obesity is a frequent metabolic disorder but an effective therapy is still scarce. Anorexigenic neuropeptides produced and acting in the brain have the potential to decrease food intake and ameliorate obesity but are ineffective after peripheral application. We have designed lipidized analogs of prolactin-releasing peptide (PrRP), which is involved in energy balance regulation as demonstrated by obesity phenotypes of both PrRP- and PrRP-receptor-knockout mice. Lipidized PrRP analogs showed binding affinity and signaling in PrRP receptor-expressing cells similar to natural PrRP. Moreover, these analogs showed high binding affinity also to anorexigenic neuropeptide FF-2 receptor. Peripheral administration of myristoylated and palmitoylated PrRP analogs to fasted mice induced strong and long-lasting anorexigenic effects and neuronal activation in the brain areas involved in food intake regulation. Two-week-long subcutaneous administration of palmitoylated PrRP31 and myristoylated PrRP20 lowered food intake, body weight and improved metabolic parameters, and attenuated lipogenesis in mice with diet-induced obesity. Our data suggest that the lipidization of PrRP enhances stability and mediates its effect in central nervous system. Strong anorexigenic and body-weight-reducing effects make lipidized PrRP an attractive candidate for anti-obesity treatment.

The objective of the current study was to search for genetic determinants associated with antihypertensive effects of angiotensin-converting enzyme (ACE) inhibitor captopril. Linkage and correlation analyses of captopril-induced effects on blood pressure (BP) with renal transcriptome were performed in the BXH/HXB recombinant inbred (RI) strains derived from spontaneously hypertensive rat (SHR) and Brown Norway (BN-Lx) progenitors. Variability of blood pressure lowering effects of captopril among RI strains was continuous suggesting a polygenic mode of inheritance. Linkage analysis of captopril-induced BP effects revealed a significant quantitative trait locus (QTL) on chromosome 15. This QTL colocalized with cis regulated expression QTL (eQTL) for the Ednrb (endothelin receptor type B) gene in the kidney (SHR allele was associated with increased renal expression) and renal expression of Ednrb correlated with captopril-induced BP effects. These results suggest that blood pressure lowering effects of ACE inhibitor captopril may be modulated by the variants at the Ednrb locus.

Increased systemic vascular resistance is responsible for blood pressure (BP) elevation in most forms of human or experimental hypertension. The enhanced contractility of structurally remodeled resistance arterioles is mediated by enhanced calcium entry (through L type voltage-dependent calcium channels – L-VDCC) and/or augmented calcium sensitization (mediated by RhoA/Rho kinase pathway). It is rather difficult to evaluate separately the role of these two pathways in BP control because BP response to the blockade of either pathway is always dependent on the concomitant activity of the complementary pathway. Moreover, vasoconstrictor systems enhance the activity of both pathways, while vasodilators attenuate them. The basal fasudil-sensitive calcium sensitization determined in rats deprived of endogenous renin-angiotensin system (RAS) and sympathetic nervous system (SNS) in which calcium entry was dose-dependently increased by L-VDCC opener BAY K8644, is smaller in spontaneously hypertensive rats (SHR) than in normotensive Wistar-Kyoto (WKY) rats. In contrast, if endogenous RAS and SNS were present in intact rats, fasudil caused a greater BP fall in SHR than WKY rats. Our in vivo experiments indicated that the endogenous pressor systems (RAS and SNS) augment calcium sensitization mediated by RhoA/Rho kinase pathway, whereas the endogenous vasodilator systems (such as nitric oxide) attenuate this pathway. However, the modulation of calcium entry and calcium sensitization by nitric oxide is strain-dependent because NO deficiency significantly augments low calcium entry in WKY and low calcium sensitization in SHR. Further in vivo and in vitro experiments should clarify the interrelationships between endogenous vasoactive systems and the contribution of calcium entry and/or calcium sensitization to BP maintenance in various forms of experimental hypertension.

Spontaneously hypertensive rats (SHR) are characterized by enhanced sympathetic vasoconstriction, whereas their vasodilator mechanisms are relatively attenuated compared to their high BP. The objective of our in vivo study was to evaluate whether the impaired function of BKCa and/or KV channels is responsible for abnormal cAMP-induced vasodilatation in genetic hypertension. Using conscious SHR and normotensive WKY rats we have shown that under the basal conditions cAMP overproduction elicited by the infusion of β-adrenoceptor agonist (isoprenaline) caused a more pronounced decrease of baseline blood pressure (BP) in SHR compared to WKY rats. Isoprenaline infusion prevented BP rises induced by acute NO synthase blockade in both strains and it also completely abolished the fully developed BP response to NO synthase blockade. These cAMP-induced vasodilator effects were diminished by the inhibition of either BKCa or KV channels in SHR but simultaneous blockade of both K+ channel types was necessary in WKY rats. Under basal conditions, the vasodilator action of both K+ channels was enhanced in SHR compared to WKY rats. However, the overall contribution of K+ channels to cAMP-induced vasodilator mechanisms is insufficient in genetic hypertension since a concurrent activation of both K+ channels by cAMP overproduction is necessary for the prevention of BP rise elicited by acute NO/cGMP deficiency in SHR. This might be caused by less effective activation of these K+ channels by cAMP in SHR. In conclusion, K+ channels seem to have higher activity in SHR, but their vasodilator action cannot match sufficiently the augmented vasoconstriction in this hypertensive strain.

Prague hereditary hypertriglyceridemic (HTG) rats constitute a genetic model of hypertension associated with hyperlipidemia and insulin resistance. Various cell alterations, including changes in membrane dynamics, ion transport, and decreased platelet responses to thrombin have been observed in this strain. As hypertriglyceridemia appears to be associated with reduced endothelium-dependent vasodilation and platelet aggregation, we examined whether triglycerides could modulate cell responsiveness through changes in cyclic nucleotides in platelets of HTG rats. From the age of 6 weeks, these hypertensive animals were subjected for 10 weeks to interventions that modified circulating triglycerides levels (2.17+/-0.09 mmol/l), leading to their reduction (gemfibrozil treatment, 0.87+/-0.05 mmol/l) or elevation (high fructose intake, 3.23+/-0.07 mmol/l). Basal cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) contents were 15% and 48% lower in isolated platelets of HTG rats than in those of Lewis controls. cAMP level was further reduced in HTG rats subjected to high fructose intake. Irrespective of their plasma triglyceride levels, the thrombin-induced increase in platelet cGMP levels present in Lewis rats was absent in platelets of HTG rats. In contrast, no strain- or treatment-related differences were observed in the magnitude or kinetics of cGMP response to exogenous nitric oxide (NO). NO-induced cGMP and cAMP changes were associated in an opposite manner with trimethylamino-diphenylhexatriene (TMA-DPH) anisotropy, a biophysical parameter that reflects the microviscosity of the outer part of the cell membrane. Our results indicate that the attenuation of platelet responsiveness to thrombin in HTG rats represents a strain difference that cannot merely be due to a difference in plasma triglyceride levels. Platelet hyporesponsiveness to agonists such as thrombin in HTG rats cannot be explained by a change in levels of inhibitory cyclic nucleotides, since they were actually found to be low and not high.

OBJECTIVE The contribution of major vasoactive systems (renin-angiotensin system, sympathetic nervous system and nitric oxide) to blood pressure maintenance and the possible involvement of superoxide anions in the reduced efficiency of nitric oxide (NO)-dependent vasodilation to counterbalance sympathetic vasoconstriction were studied in salt-hypertensive Dahl rats. DESIGN AND METHODS We used Dahl salt-sensitive (SS/Jr) and salt-resistant (SR/Jr) female rats kept on a low-salt (0.3% NaCl) or high-salt diet (8% NaCl) for 6 weeks since weaning. Mean arterial pressure (MAP) was measured in conscious animals subjected to acute consecutive blockade of the renin-angiotensin system (RAS) [captopril, 10 mg/kg intravenously (i.v.)], the sympathetic nervous system (SNS) (pentolinium, 5 mg/kg i.v.) and NO synthase (Nomega-nitro-L-arginine methyl ester (L-NAME), 30 mg/kg i.v.). Before the consecutive blockade of vasoactive systems one-half of the animals in each experimental group was pre-treated with a stable membrane-permeable mimetic of superoxide dismutase (tempol, 25 mg/kg i.v.) which functions as a superoxide scavenger. RESULTS Compared to normotensive SR/Jr animals, salt-hypertensive SS/Jr rats were characterized by an enhanced blood pressure (BP) fall after ganglionic blockade (-104 +/- 8 versus -62 +/- 5 mm Hg, P < 0.001) and by higher residual blood pressure recorded after the blockade of both RAS and SNS (70 +/- 3 versus 43 +/- 3 mmHg, P < 0.01), but there was only a borderline elevation of their BP response to acute NO synthase inhibition (67 +/- 6 versus 49 +/- 4 mmHg, P < 0.05). The acute tempol pre-treatment elicited the most pronounced reduction of basal BP (-13 +/- 1 mmHg, P < 0.001) in the salt-hypertensive SS/Jr group in which the BP rise after L-NAME administration was augmented by about 50%. On the contrary, tempol pre-treatment did not affect norepinephrine- or angiotensin II-dependent vasoconstriction. CONCLUSIONS The NO system is not able to counterbalance effectively the hyperactivity of the sympathetic nervous system in salt-hypertensive Dahl rats. The predominance of sympathetic vasoconstriction over NO-dependent vasodilation could be explained partially by enhanced NO inactivation due to augmented superoxide anion formation in hypertensive animals.

The role of the enzyme 11beta-hydroxysteroid dehydrogenase (11betaHSD) in hypertension remains unknown even if it appears that the inappropriately decreased 11betaHSD activity might be involved in a process that leads to high blood pressure. The possible changes of 11betaHSD were therefore investigated in rats with spontaneous or salt-induced hypertension. The adult male rats of the following genotypes were used: spontaneously hypertensive rats (SHR), normotensive Wistar-Kyoto rats (WKY), Dahl salt-sensitive rats fed either a high-salt diet containing 8% NaCl (DS-HS) or low-salt diet containing 0.2% NaCl (DS-LS), and Dahl salt-resistant rats fed the same diets (DR-HS, DR-LS). 11betaHSD was investigated in colon, aorta, renal cortex, and renal medulla and was assessed as percentage conversion of [3H]corticosterone to [3H]11-dehydrocorticosterone in the presence of NAD or NADP. The results demonstrated that genotype exerts a significant effect on 11betaHSD. 11betaHSD activity was significantly increased in colon and renal medulla of SHR compared with WKY rats. No significant differences were observed in renal cortex and aorta. In Dahl rats kept on a low-salt diet, 11betaHSD activity was significantly higher in colon, renal medulla, and cortex of DS-LS than in DR-LS rats but no difference was observed in aorta. The differences disappeared in age-matched DS and DR rats fed the high-salt diet. Increased dietary sodium intake stimulated the activity of 11betaHSD in renal cortex and medulla of DR rats and decreased the activity in colon of DS rats. We conclude that the development of spontaneous and salt-induced hypertension is not associated with decreased activity of 11betaHSD. However, the results showed that salt intake is able to modulate the activity of 11betaHSD and that 11betaHSD in DS and DR rats responds to high dietary salt intake in a different manner.

Higher male sensitivity to atherosclerotic and hypertensive events was a reason to study sex differences in migration and proliferation of vascular smooth muscle cells (VSMC) isolated from male and female spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) controls. Outgrowth of cells from explants, doubling time, curves of cumulative labeling and the length of cell cycle were measured in aortic VSMC. Systolic and mean arterial pressures were higher in males than in females of the two strains. The migration of cells from male explants was significantly faster than those from female aortas in both strains. The doubling time was always shorter in male VSMC than in those from females and this was more apparent in the late exponential phase of growth. The thymidine incorporation into newly synthesized DNA, which was enhanced in SHR compared to WKY cells, was also higher in male cells compared to female ones. Cell cycle was always shorter in male than in female VSMC due to the shorter G1 phase. In contrast, shorter S phase caused shorter cell cycle in SHR compared to WKY VSMC. Consequently, the shortest cell cycle was found in VSMC from SHR males with the highest blood pressure. It can be concluded that gender and genotype are two independent factors participating in the control of migration and proliferation of VSMC.

Neurogenic pulmonary edema is an acute life-threatening complication of central nervous system injury. We introduce a hypothesis that early i.v. administration of high-dose atropine can prevent neurogenic pulmonary edema development on the basis of the prevention of baroreflex-induced bradycardia, which was recognized as a major factor in neurogenic pulmonary edema formation. To validate this hypothesis, a clinical trial in patients suffering from subarachnoid haemorrhage should be performed, with atropine administered i.v. immediately after the maintenance of the living functions, intubation and ability to monitor patient.

Objective To determine the relationships between blood pressure, membrane microviscosity, plasma lipids and cytosolic pH in Dahl rats susceptible or resistant to salt hypertension. Design and methods Blood pressure, plasma triglycerides and total cholesterol, platelet cytosolic pH (pH i ) and the microviscosity of both outer membrane leaflet (TMA-DPH fluorescence anisotropy) and membrane lipid core (DPH fluorescence anisotropy) were studied in platelets and erythrocyte ghosts of Dahl salt-sensitive (SS/Jr) and salt-resistant (SR/Jr) rats fed either a low-salt diet (0.3% NaCI) until the age of 9, 15 or 24 weeks or a high-salt diet (4% NaCI) for 5 or 10 weeks after weaning. Results At low salt intake, DPH but not TMA-DPH anisotropy increased with age in platelets of SS/Jr rats. Chronic high salt intake was accompanied by an increase of DPH anisotropy in platelets but not in erythrocyte ghosts of SS/Jr rats. Platelet DPH anisotropy correlated positively with blood pressure of salt-loaded SS/Jr rats. Chronic high salt intake also reduced pH i in platelets, the regulation of which seemed to be related to the changes in TMA-DPH anisotropy. This especially concerns the thrombin-induced pH i rise which was inversely related to basal pH i , plasma lipids and TMA-DPH anisotropy. Altered membrane lipid composition might be the underlying mechanism because both membrane microviscosity and platelet pH i regulation were reported to correlate significantly with plasma triglycerides and/or cholesterol. Conclusions Platelets of salt hypertensive Dahl rats are characterized by an increased microviscosity of membrane lipid core which correlated positively with blood pressure. The major influence of plasma triglycerides on DPH anisotropy should be taken into consideration when investigating the links between membrane microviscosity and blood pressure. On the other hand, the changes in microviscosity of the outer membrane leaflet might be involved in pH i regulation (probably through control of the Na + /H + exchanger).

In this review, we attempt to outline the age-dependent interactions of principal systems controlling the structure and function of the cardiovascular system in immature rats developing hypertension. We focus our attention on the cardiovascular effects of various pharmacological, nutritional, and behavioral interventions applied at different stages of ontogeny. Several distinct critical periods (developmental windows), in which particular stimuli affect the further development of the cardiovascular phenotype, are specified in the rat. It is evident that short-term transient treatment of genetically hypertensive rats with certain antihypertensive drugs in prepuberty and puberty (at the age of 4–10 wk) has long-term beneficial effects on further development of their cardiovascular apparatus. This juvenile critical period coincides with the period of high susceptibility to the hypertensive effects of increased salt intake. If the hypertensive process develops after this critical period (due to early antihypertensive treatment or late administration of certain hypertensive stimuli, e.g., high salt intake), blood pressure elevation, cardiovascular hypertrophy, connective tissue accumulation, and end-organ damage are considerably attenuated compared with rats developing hypertension during the juvenile critical period. As far as the role of various electrolytes in blood pressure modulation is concerned, prohypertensive effects of dietary Na+and antihypertensive effects of dietary Ca2+are enhanced in immature animals, whereas vascular protective and antihypertensive effects of dietary K+are almost independent of age. At a given level of dietary electrolyte intake, the balance between dietary carbohydrate and fat intake can modify blood pressure even in rats with established hypertension, but dietary protein intake affects the blood pressure development in immature animals only. Dietary protein restriction during gestation, as well as altered mother-offspring interactions in the suckling period, might have important long-term hypertensive consequences. The critical periods (developmental windows) should be respected in the future pharmacological or gene therapy of human hypertension.

Objective To search for alterations of cytosolic pH and cell calcium handling in platelets and erythrocytes of Dahl rats susceptible and resistant to salt-induced hypertension. Design and methods Blood pressure, plasma lipids, platelet cytosolic calcium concentration ([Ca 2+ ] i ) and pH (pH,) together with thrombin-induced changes in these parameters as well as erythrocyte [Ca 2+ ] i and 45 Ca influx were determined in Dahl salt-sensitive (SS/Jr) and salt-resistant (SR/Jr) rats aged 9, 15 and 24 weeks, which were fed a low-salt diet (0.3% NaCI), and in animals fed high-salt diet (4% NaCI) for 5-10 weeks since weaning. Results With a low salt intake platelet pH i was lower in SS/Jr than it was in SR/Jr rats, whereas basal platelet [Ca 2+ ] i was similar in rats of both strains. The difference in basal pH i between SS/Jr and SR/Jr rats increased progressively with age of animals. A high salt intake from youth did not influence platelet [Ca 2+ ] i in rats of either strain but it caused an earlier decrease in pH i in SR/Jr than it did in SS/Jr rats. Thrombin stimulation induced similar elevations of pH i and [Ca 2+ ] i in rats of both strains, irrespective of age, salt intake and response of blood pressure to salt intake. Erythrocyte 45 Ca influx and [Ca 2+ ] i were greater for SS/Jr rats but only the latter parameter was correlated positively to blood pressure. Both regulation of platelet pH i and erythrocyte Ca 2+ handling were significantly related to plasma lipid levels. Conclusions Platelets of SS/Jr rats fed a low-salt diet were characterized by a lower basal cytosolic pH i but unchanged [Ca 2+ ] i relative to those of SR/Jr rats. Hypertension induced by high salt intake was associated with increased erythrocyte [Ca 2+ ] i but not with elevation of platelet [Ca 2+ ] i or alteration of response to stimulation with thrombin.

To define better the relationships between lipid metabolism disturbances and platelet aggregation we have examined these parameters in hereditary hypertriglyceridemic and control Lewis rats. Hereditary hypertriglyceridemic rats are hypertensive and have high plasma triglycerides but not elevated plasma total cholesterol. In the present study, we have demonstrated that platelets from hereditary hypertriglyceridemic rats have lowered initial rate and maximal aggregation after stimulation with thrombin or ADP in comparison with controls. These two strains did not differ significantly in the inhibition of platelet aggregation by the thromboxane A2 receptor inhibitor, SQ 29 548. In hereditary hypertriglyceridemic rats, the thrombin response, as well as the contribution of the thromboxane A2-sensitive pathway, were positively associated with the plasma level of triglycerides. Similar trend was found in Lewis rats. However, the slopes of these relationships were reduced in hereditary hypertriglyceridemic rats. These alterations of the aggregatory responses in hereditary hypertriglyceridemic rats were independent of blood pressure and plasma cholesterol level. In conclusion, our results showed a clear-cut platelet hypoaggregability to both thrombin and ADP in hypertensive hypertriglyceridemic rats. This hypoaggregability was not due to an impaired function of the thromboxane A2 pathway but could be connected with disturbances of lipid metabolism.

Abstract Ion transport abnormalities in essential hypertension are often associated with concomitant changes of lipid metabolism, but this information is missing in rats with genetic hypertension. We therefore studied the alterations of red cell Na + and K + transport and their relationship to blood pressure and plasma lipids (cholesterol and triglycerides) in Prague hereditary hypertriglyceridemic (HTG) rats, Lyon hypertensive (LH) rats, and HTG×Lewis F 2 hybrids. In both hypertensive models and F 2 hybrids, red cell Na + content (Na + i ) was positively related to plasma triglycerides but not to plasma cholesterol levels. Na + i elevation was more pronounced in HTG than in LH rats, probably due to higher plasma triglycerides in the former strain. The two hypertensive strains differed in bumetanide-sensitive Na + transport, which was augmented in HTG rats with low plasma cholesterol but suppressed in LH rats characterized by high cholesterol levels. In the two genetic models, there was a positive association of blood pressure with Na + leak, and this was also confirmed by the cosegregation of these parameters in F 2 hybrids. We conclude that the enhancement of Na + leak represents the major ion transport abnormality in rats with genetic hypertension. The alterations in plasma lipids are important determinants of abnormal red cell ion transport in hypertensive models studied. Although the detailed mechanism of their participation in ion transport regulation is still not completely understood, triglyceride-dependent changes in membrane microviscosity seem to be responsible for the modulation of particular ion transport pathways.

Nonenzymatic collagen glycation and modification with lipid derived metabolites was studied in rat skin and tail tendon collagen of control and hypertriglyceridemic (HTG) rats. Age-dependent changes typical for lipid and sugar derived adducts were evaluated by measuring fluorescence of these collagens at wavelengths typical for sugar ( 335 385 and 370 440 nm) and lipid derived adducts ( 356 460 and 390 460 nm). In addition pentosidine assay (corresponding to the fluorescence parameters 335 385 nm) was performed as well. It was found that pentosidine concentration as well as fluorescence intensities in skin collagen was the same for control and HTG rats and significantly increased with age. On the other hand, no significant age-dependent changes in fluorescence intensities were observed in tail tendon collagen. Pentosidine concentration in tail tendon collagen was much lower than that in skin and it was decreased in young HTG rats compared to cotrol ones. It increased with age, more distinctly in HTG rats than in their control counterparts, in such a way that at the age of 19 months the pentosidine levels were undistinguishible in both rat strains. Possible mechanisms underlying these results are discussed.

The objective of this study was to evaluate whether the major histocompatibility complex of the rat can be related to blood pressure (BP) level and BP response to stress. Blood pressure was determined under light ether anesthesia or during moderate restraint stress in normotensive Lewis rats, in rat strains congenic with respect to their RT1 haplotype [LEW.1A (RT1 a ) and LEW.1W (RT1 u )], and in their recombinant lines LEW.1AR1 (RT1 ar1 ), LEW.1AR2 (RT1 ar2 ), LEW.1WR1 (RT1 wr1 ), and LEW.1WR2 (RT1 wr2 ). Under light ether anesthesia, systolic blood pressure was similar in Lewis, LEW.1A, and LEW.1W rats. There were also no significant differences in blood pressure in LEW.1AR1 and LEW.1AR2 animals when compared with Lewis or LEW.1A rats. In contrast, BP was significantly increased in LEW.1WR2 rats. On the other hand, moderate restraint stress induced a BP increase in animals of all recombinant lines compared to the respective congenic strains. These results confirmed our previous finding in recombinant inbred strains about the significant role of RT1 complex in BP regulation. Moreover, our data indicated that BP can be influenced by interaction of individual regions of the RT1 complex on the genetic background of Lewis strain. Am J Hypertens 1996;9:675–680

Hereditary hypertriglyceridemic rats (hHTg) were developed as a new genetic model for the study of relationships between blood pressure (BP) and metabolic abnormalities. This strain has been produced by selective inbreeding from Wistar rats according to the rise of plasma triglycerides induced by a high-sucrose diet. Though hHTg rats display hypertriglyceridemia, impaired glucose tolerance, hyperinsulinemia, insulin resistance and increased BP even without nutritional stimuli, high sucrose feeding further aggravates these symptoms. High plasma triglycerides levels in hHTg rats seem to be a consequence of their hyperproduction. Impaired insulin action is responsible for the defective glucoregulation in this strain. The loss of insulin responsiveness might be due to a reduction in the number of glucose transporters. Highly significant relationships among plasma triglycerides, ouabain-resistant Na+ transport and BP were demonstrated in the hHTg rats. Segregating populations (F2 hybrids) should be used for genetic analysis of the primary role of lipid and/or ion transport abnormalities in the pathogenesis of this form of genetic hypertension.

Aims Human genome-wide association studies (GWAS) of hypertension identified only few susceptibility loci with large effect that were replicated across populations. The vast majority of genes detected by GWAS has small effect and the regulatory mechanisms through which these genetic variants cause disease remain mostly unclear. Here, we used comparative genomics between human and an established rat model of hypertension to explore the transcriptional mechanisms mediating the effect of genes identified in 15 hypertension GWAS. Methods and results Time series analysis of radiotelemetric blood pressure (BP) was performed to assess 11 parameters of BP variation in recombinant inbred strains derived from the spontaneously hypertensive rat. BP data were integrated with ∼27 000 expression quantative trait loci (eQTLs) mapped across seven tissues, detecting >8000 significant associations between eQTL genes and BP variation in the rat. We then compiled a large catalogue of human genes from GWAS of hypertension and identified a subset of 2292 rat–human orthologous genes. Expression levels for 795 (34%) of these genes correlated with BP variation across rat tissues: 51 genes were cis-regulated, whereas 459 were trans-regulated and enriched for ‘calcium signalling pathway’ ( P = 9.6 × 10−6) and ‘ion channel’ genes ( P = 3.5 × 10−7), which are important determinants of hypertension. We identified 158 clusters of trans-eQTLs, annotated the underlying ‘master regulator’ genes and found significant over-representation in the human hypertension gene set (enrichment P = 5 × 10−4). Conclusion We showed extensive conservation of trans-regulated genes and their master regulators between rat and human hypertension. These findings reveal that small-effect genes associated with hypertension by human GWAS are likely to exert their action through coordinate regulation of pathogenic pathways.

Aim It is well-known that salt hypertension is associated with increased oxidative stress. Since the development of salt hypertension is age-dependent, we were interested whether young and adult salt hypertensive Dahl rats differ in oxidative stress level and/or in the effects of chronic antioxidant therapy on blood pressure (BP) level and on the participation of particular vasoconstrictor/vasodilator systems in BP maintenance. Methods Young (5-week-old) and adult (12-week-old) salt-sensitive (Dahl-S) male rats were fed high-salt diet (5% NaCl) and drank tempol solution (2 mm) for 5 weeks. BP was monitored with radiotelemetry and vasoconstrictor/vasodilator balance was evaluated at the end of experiment. Moreover, NO synthase activity, superoxide production and lipoperoxidation were determined in heart, kidney and aorta in separate subgroups of Dahl rats. Results Tempol treatment had quite opposite BP effects in young and adult Dahl-S rats. While it tended to increase BP in young salt hypertensive Dahl-S rats, it significantly lowered BP in the adult ones due to reduced sympathetic vasoconstriction. Importantly, high salt intake substantially reduced NO synthase activity in heart and kidney, and markedly increased superoxide production in kidneys and aorta of adult Dahl-S rats in which BP correlated positively with superoxide production in thoracic aorta and lipoperoxidation in kidneys. Conclusion Chronic antioxidant therapy lowered BP only in adult salt hypertensive Dahl-S rats in which superoxide levels were increased in both kidneys and aorta. Blood pressure reduction induced by chronic tempol treatment is related to attenuated sympathetic vasoconstriction rather than to augmented NO-dependent vasodilatation.

Hypertension often results in left ventricular hypertrophy (LVH), defined as a major risk factor for cardiovascular morbidity and mortality. In its initial stages, the hypertrophied ventricle compensates an overload, but later on, the diastolic and eventually also systolic properties of left ventricle (LV) become impaired causing the decompensation and finally the heart failure (HF). Although in animals the LVH can be prevented by pharmacological therapy, in man LVH can be reduced only to a limited extent. This could be related to the fact that most of the human studies are too short and the duration of particular stimuli is not exactly known. Moreover, if the therapy is not applied in a precise developmental window, the results may be subtle or none. There is no doubt that angiotensin converting enzyme (ACE) inhibitors and AT1 blockers are currently the drugs of the first choice in the treatment of essential hypertension. Besides the effect of these drugs on blood pressure (BP) per se they also have a potential to normalize cardiovascular structural changes. HF is continuously increasing in the Western world. The population-based Framingham study suggested that the prognosis in women is significantly better than in men after the onset of HF. What is the reason for such gender differences is not fully understood.