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Purpose: To determine whether useful images of the optic discs of conscious rats and mice can be obtained by using a photo slit lamp and a modified Goldmann-type fundus contact lens., Methods: Testing was performed with a photo slit lamp equipped with two 2x teleconverters and a digital camera through a Goldmann-type fundus contact lens that was fabricated for the rodent eye., Results: Images of the rat and mouse optic discs were obtained that are comparable to those used by ophthalmologists to assess optic neuropathy in glaucoma, a key part of the standard of care and of clinical investigation of this disease. The cup in the optic disc image of these rodents is darker than the neural rim of the disc, rather than lighter, as it is in humans., Conclusions: In addition to the application of this imaging method to studies of the effect on optic disc cupping of induced increased intraocular pressure in rats and mice, by detecting and documenting the onset and the course of optic neuropathy, it should be valuable in identifying animal models of glaucoma, in studying neuropathogenic mechanisms, and in assessing the effects of experimental therapies.

Background- Clonidine has an antihypertensive effect by its action in the brain and, because we observed that the tonic production of nitric oxide (NO) in the brain is required to maintain blood pressure at its low, normotensive level, the current study was designed to determine whether the hypotensive action of clonidine resulted from its stimulation of excess NO in the brain. Methods and Results- Porphyritic microsensors were used to quantify NO concentration in the nucleus tractus solitarius (NTS) in vitro in brain slices and in vivo in the anesthetized rat. In both preparations, the basal production of NO in the NTS was 15+/-3 nmol/L. In vitro stimulation of the NTS with clonidine (50 nmol/L) resulted in an increase in the NO concentration to 84+/-7 nmol/L. In vivo, the intracerebroventricular (ICV) infusion of clonidine (0.03 microgram) caused an increase in NO concentration in the NTS to 128+/-17 nmol/L. This ICV injection of clonidine caused a fall in mean arterial pressure of -22+/-1 mm Hg and a decrease of heart rate of -18+/-2%. The blockade of NO production with N(G)-nitro-L-arginine-methyl ester (2 micromol; delivered ICV, 30 minutes before the clonidine) reduced responses to clonidine for both mean arterial pressure and heart rate (-3+/-1 mm Hg and -2+/-1% change, respectively). Conclusion- The stimulation of the release of NO in the brain by clonidine contributes to its central antihypertensive action.

Purpose: To determine whether the Goldmann applanation tonometer can be modified to measure intraocular pressure (IOP) in the awake mouse., Methods: Tonometers with reduction of the biprism angles in the applanating tips and in the weight applied by the instrument were tested in anesthetized mice in calibration experiments. Then a tonometer with the appropriate configuration of tip and weight was used in conscious, unsedated mice., Results: Tonometry in mice required a biprism angle of 36 degrees and weight applied of 25 mg per scale division (2 g full scale). This tonometer was calibrated in mice against manometrically measured IOP and showed good agreement across the range of IOP tested (0-50 mm Hg). In conscious mice the measured mean Goldmann value was 13.7 +/- 3.2 mm Hg (mean +/- SD; 95% confidence interval, 13.1, 14.2 mm Hg)., Conclusions: The Goldmann tonometer, the standard for measuring the IOP in the human eye, was modified to measure this fundamental physiologic parameter in the awake mouse. This measurement is required to confirm success in genetically engineering a model in the powerful mouse system, which mimics elevated IOP in humans. The model will open new avenues for studying the causes of the optic neuropathy of glaucoma, the regulation of IOP, and new therapeutic approaches to prevent the irreversible loss of vision from this disease.

Purpose: To determine whether the Goldmann applanation tonometer can be modified to measure intraocular pressure (IOP) in the conscious rat., Methods: In anesthetized rats Goldmann tonometers were tested that had reduced biprism angles in the applanating tips and reduced weights in the tonometer body from those used in humans and species with similar size eyes. Tonometers with tips with biprism angles of 48 degrees and an applied weight of 25 mg per Goldmann scale division (2 g full scale) were calibrated for the rat against manometrically measured IOP. Tonometers, thus modified, were then used in conscious, unsedated rats., Results: In conscious rats the measured mean Goldmann value was 15.5 +/- 0.6 mm Hg (confidence interval = 14.1, 16.6 mm Hg). This was the plateau level reached after the repeated applanations (approximately 10) required to eliminate an artifactual decline in initial Goldmann readings, which was larger than that in humans., Conclusions: The Goldmann applanation tonometer was modified to measure IOP in the conscious, unsedated rat. This instrument, the standard for measuring this key physiological parameter in the human eye, can now be applied to the laboratory rat. This may advance the use of this important animal as a model in IOP and glaucoma research.

The purpose of this study was to examine the role played by a deficit in nitric oxide (NO) in contributing to the large cerebral infarcts seen in hypertension. Cerebral infarction was produced in rats by occlusion of the middle cerebral artery (MCA). Studies were performed in Sprague-Dawley (SD) rats subjected to NO synthase blockade (N(G)-nitro-L-arginine [L-NNA], 20 mg x kg(-1) x d(-1) in drinking water) and in spontaneously hypertensive stroke-prone rats (SHRSP). NO released in the brain in response to MCA occlusion was monitored with a porphyrinic microsensor in Wistar-Kyoto rats. The increment in NO released with MCA occlusion was 1.31+/-0.05 micromol/L in L-NNA-treated rats, 1.25+/-0.04 micromol/L in SHRSP, 2. 24+/-0.07 micromol/L in control SD rats, and 2.25+/-0.06 micromol/L in Wistar-Kyoto rats (P<0.0001 for control versus the other groups). Infarct sizes in the L-NNA-treated and control SD rats were 8.50+/-0. 8% and 5.22+/-0.7% of the brain weights, respectively (P<0.05). The basilar arterial wall was significantly thicker in L-NNA-treated rats compared with their controls. We conclude that both the deficit in NO and the greater wall thickness contribute to the larger infarct size resulting from MCA occlusion in SHRSP and in L-NNA-treated rats compared with their respective controls.

Much attention has been focused on the role of nitric oxide in hypertension and cardiovascular disease. More recently, the role of superoxide anion and its interaction with nitric oxide has been investigated in this context. This review will concentrate on the role of superoxide in human and experimental hypertension, paying particular attention to the potential sources of superoxide within the vasculature and discussing some of the molecular mechanisms surrounding its production and dismutation. We discuss what is known about the human superoxide dismutase enzymes. We conclude that the balance between nitric oxide and superoxide is more important than the absolute levels of either alone.

Purpose: To develop a method for measurement of intraocular pressure in conscious, unsedated rats. METHODS. The animal was gently held with a thick fabric mitten, topical anesthetic drops were instilled and the Tono-Pen was applied to the cornea., Result: Measurements in a total of 51 animals did not differ significantly among four strains studied: the overall mean intraocular pressure+/-standard deviation was 13.0+/-1.2 mm Hg. Several intraocular pressure tolerance limits were calculated from this conscious rat data to provide a baseline estimate for future studies., Conclusions: This measurement method in conscious rats may contribute to making this widely used laboratory animal available for intraocular pressure research.

We studied the mechanisms responsible for vascular and cardiac hypertrophy in hypertension (pressure load and humoral and genetic factors) in two experimental approaches: (1) We carried out a cosegregation analysis to correlate cardiac and vascular hypertrophy with subphenotypes of blood pressure in an F2 generation of a cross between stroke-prone spontaneously hypertensive rats (SHRSP) and normotensive Wistar-Kyoto rats; (2) we treated 8-week-old SHRSP with perindopril, an angiotensin-converting enzyme inhibitor; losartan, an angiotensin type 1 receptor antagonist; or perindopril combined with a nitric oxide synthase inhibitor to investigate the relative contributions of blood pressure and angiotensin II to the pathogenesis of cardiac hypertrophy and vascular smooth muscle polyploidy. Vascular smooth muscle polyploidy was measured with flow cytometry DNA analysis. Cardiac hypertrophy was assessed by measuring the ratios of heart weight to body weight and left ventricle + septum weight to body weight. Blood pressure was measured with radiotelemetry in the F2 cosegregation experiment and with tail-cuff plethysmography in the pharmacological study. In the F2 rats, the best predictor of smooth muscle polyploidy by ANCOVA was systolic pressure (F=29.28, P < .0001). The ratio of left ventricle + septum weight to body weight had four major predictors: the male progenitor of the cross, sex, pulse pressure, and change in systolic pressure during salt (F=43.67, P < .0001; F=16.37, P < .0001; F=8.41, P=.0022; and F=12.39, P= .0003, respectively). The ratio of heart weight to body weight had similar predictors. In the pharmacological study, treatment with losartan alone, perindopril alone, or perindopril in combination with N(G)-nitro-L-arginine methyl ester prevented the development of smooth muscle polyploidy and cardiac hypertrophy. The prevention of cardiac hypertrophy was most marked in the SHRSP treated with perindopril plus N(G)-nitro-L-arginine methyl ester, despite blood pressure being higher in this group than in the two other treatment groups. We conclude that vascular and cardiac hypertrophy in this form of hypertension are regulated by different variables. However, suppression of the action of angiotensin II lessens hypertrophy of both types of muscle.

Insight is rapidly developing into the physiological production and function of nitric oxide. This small molecule has several physiological actions that oppose the pathogenesis of hypertension. Originating in the endothelium, it causes vascular smooth muscle relaxation, lowering blood pressure. In the central nervous system nitric oxide tonically depresses activity of the sympathetic nervous system, and in the kidney it regulates renin release and causes natriuresis. Nitric oxide may also contribute to the protective action of oestrogen.

Inhibition of NO synthase (NOS) in the central nervous system (CNS) causes a pressor response. This observation indicates that NO is normally produced at CNS site(s) where it has a tonic blood pressure lowering effect. The current study tests the hypothesis that a deficient NOS activity in the CNS may contribute to the pressure elevation in genetically hypertensive rats. NO administered intracerebroventricularly (ICV) caused a greater fall in mean arterial pressure (MAP; femoral artery) in hypertensive (SHRSP) than in normotensive (WKY) rats, -66.1 +/- 3.4 mm Hg v -23.7 +/- 3.9 mm Hg, respectively. Yet when endogenous NO was increased by stimulating NOS with ICV calcium, the depressor response was less in SHRSP than in WKY, 13.7 +/- 1.1 mm Hg v 26.7 +/- 1.9 mm Hg. Likewise, when NOS was blocked with N omega- nitro-L-arginine methyl ester (L-NAME), the resultant pressor response was less in SHRSP than in WKY, 13.8 +/- 1.1 mm Hg v 22.2 +/- 1.1 mm Hg. Blockade of the action of cGMP, a mediator of the action of NO, caused a pressor response of 6.0 +/- 2.8 mm Hg and 22.6 +/- 8.7 mm Hg (P < .01) in the hypertensive and normotensive rats, respectively. Electrolytic ablation of the anteroventral third cerebral ventricle (AV3V) did not alter blood pressure responses to NO or to agents that alter NOS activity. We conclude that a deficit in NOS activity in some other central cardiovascular regulatory area may contribute to the elevated arterial pressure of these genetically hypertensive rats.

We undertook these studies to determine whether a deficient nitric oxide production in genetically hypertensive rats could result from its being scavenged by an excess production of superoxide. In one study we used a porphyrinic microsensor to measure nitric oxide concentrations released by cultured endothelial cells from stroke-prone spontaneously hypertensive rats (SHRSP) and normotensive Wistar-Kyoto rats (WKY). SHRSP cells released only about one third the concentration of nitric oxide as did WKY cells. Treatment of cells with superoxide dismutase increased nitric oxide release, demonstrating that normally nitric oxide is scavenged by endogenous superoxide. The increase in nitric oxide release in response to superoxide dismutase treatment was more than twice as great from SHRSP as from WKY cells, demonstrating the greater amount of superoxide in the hypertensive rats. A direct measure of superoxide with the use of lucigenin demonstrated the presence of 68.1 +/- 7.1 and 27.4 +/- 3.5 nmol/L of this anion in SHRSP and WKY endothelial cells, respectively. The presence of superoxide in the rat aorta was also estimated by quantification of its effect on carbachol relaxation. This relaxation was diminished when endogenous superoxide dismutase was blocked by diethyldithiocarbamic acid. This blockade reduced the relaxation by 51.2 +/- 5.2% in SHRSP aortas and by only 22.0 +/- 8.2% (P = .015) in WKY aortas. Data from these diverse systems are in agreement that superoxide production is excessive in SHRSP tissues. This excess superoxide, by scavenging endothelial nitric oxide, could contribute to the increased vascular smooth muscle contraction and hence to the elevated total peripheral resistance of these rats.

We examined the mechanism by which cobalt causes contraction of vascular smooth muscle (VSM), determining whether contractile response of VSM from normotensive and hypertensive rats differed. Contraction of rings of rat thoracic aorta from normotensive Wistar-Kyoto rats (WKY) and hypertensive spontaneously hypertensive stroke-prone rats (SHRSP) in response to addition of cobalt chloride to the muscle bath was recorded. Threshold contraction occurred at 3 microM; maximum contraction occurred at 100 microM. There was no difference between rings from WKY and SHRSP in sensitivity or maximum response to cobalt. No contractile response occurred when cobalt was added to a calcium-free physiologic salt solution (PSS) to which 1.0 mM EGTA had been added. When no EGTA was added to the PSS, cobalt caused a contraction 20% as great as that observed in calcium-containing physiologic salt solution, but this small contraction was eliminated after intracellular sequestration of calcium had been prevented by treatment of the rings with cyclopiazonic acid (3 x 10(-4) M). A concentration-dependent contraction occurred when calcium was added back to the bath in the presence of cobalt. The contraction in response to this addition of calcium did not differ between rings from WKY and SHRSP. Threshold concentrations of cobalt produced marked potentiations of contractile responses to either norepinephrine (NE) or KCl. We conclude that cobalt causes contraction by activating both voltage-sensitive and receptor-operated calcium channels in the plasma membrane. Cobalt also caused release of intracellularly sequestered calcium. There was no difference between the responses to cobalt of VSM from WKY and SHRSP.

We measured membrane fluidity and fatty acid composition in cultured vascular smooth muscle cells from stroke-prone spontaneously hypertensive and Wistar-Kyoto normotensive rats. Membrane fluidity was measured as a lateral diffusion of 5 N (octadecanoyl) aminofluorescein using fluorescence microscopy and fluorescence recovery after photobleaching. Fatty acid composition of membrane fractions was measured using high performance liquid chromatography. Lateral diffusion was significantly lower (the membrane had lower fluidity) in vascular smooth muscle cells from stroke-prone spontaneously hypertensive rats as compared to those cells isolated from Wistar-Kyoto reference strain. The ratio of arachidonic acid to total fatty acids was 0.058 +/- 0.007 in the plasma membrane from stroke-prone spontaneously hypertensive rats and 0.036 +/- 0.005 in that from Wistar-Kyoto rats, P = .005. Similarly, the ratios of arachidonic to oleic acid and arachidonic to palmitic acid were significantly greater in cells from stroke-prone spontaneously hypertensive rats (P = .002 for difference in each ratio). These results show decreased lateral diffusion (decreased membrane fluidity) in vascular smooth muscle cells from stroke-prone spontaneously hypertensive rats. This is associated with increased content of arachidonic acid, the major precursor of prostaglandins and other eicosanoids. We postulate that local changes in the unsaturated fatty acid composition related to arachidonic acid storage and release contribute to reduced membrane fluidity in stroke-prone spontaneously hypertensive rats.

Objective: To determine whether elevated microviscosity is associated with elevated arterial pressure in segregating (F2) hybrids produced by crossing stroke-prone spontaneously hypertensive rats (SHRSP) and Wistar-Kyoto (WKY) rats., Methods: SHRSP and WKY rats were obtained from the colony at the University of Heidelberg. F2 progeny were obtained by brother-sister mating of the F1 progeny of the cross between SHRSP and WKY rats. Membrane microviscosity (the inverse of fluidity) was measured as a fluorescence anisotropy of trimethylammonium diphenylhexatriene incubated with the erythrocyte membranes. The measurements were made using a luminescence spectrometer with computer-controlled excitation and emission polarizers., Results: Membrane microviscosity was significantly greater (fluidity was lower) in erythrocyte membranes obtained from SHRSP than in those obtained from WKY rats. In the F2 cohort there were no significant correlations between membrane microviscosity and systolic blood pressure, diastolic blood pressure, salt-loaded systolic blood pressure or salt-loaded diastolic blood pressure. A similar lack of relationship between these parameters was shown in a subgroup analysis, in which males or females with a male WKY rat progenitor and males or females with a male SHRSP progenitor were analysed separately., Conclusions: Erythrocyte membrane microviscosity is elevated in SHRSP compared with WKY rats. In segregating F2 hybrid rats the membrane microviscosity trait does not correlate with blood pressure. These results eliminate the microviscosity trait as being directly related to the cause of genetic differences in blood pressure between WKY rats and SHRSP.

Vascular reactivity and systolic blood pressure (SBP) were studied in tail artery rings isolated from stroke-prone spontaneously hypertensive rats (SHRSP) and normotensive, Wistar-Kyoto rats (WKY). After a control week on a diet with 1% of calcium, the animals were randomly assigned to three groups, which were fed with 1% (control), 0.4% (low) or 2.5% (high) dietary calcium. Both vascular reactivity and SBP were studied in the same animal during 9 weeks after changing diets. In the SHRSP rats on high Ca diet, maximal contractile responses to norepinephrine and serotonin (10(-10) to 10(-4) M) and to KCl (5 to 105 mM) were markedly decreased at the end of the study with respect to the control diet. These vascular changes were accompanied by a decrease of SBP in the same animals. Low calcium diet prevented the age-related increase of SBP in SHRSP rats and produced vascular changes of a lesser magnitude. WKY rats showed no significant modifications of SBP or vascular reactivity. Since plasmatic Ca2+ levels were not altered, the changes detected could not be attributed to a direct depressant effect of high calcium on the vascular smooth muscle cell (i.e. a "stabilizing action" of calcium). It is speculated that high dietary calcium could modulate the synthesis of calcium binding proteins of the plasma membrane, decreasing vascular reactivity and the elevated vascular resistance which is usually present in hypertension.

Membrane microviscosity, phospholipid composition, and turnover were measured in cultured vascular smooth muscle cells isolated from mesenteric arteries of stroke-prone spontaneously hypertensive and age-matched, normotensive Wistar-Kyoto rats. Membrane microviscosity, measured with fluorescence polarization, revealed greater microviscosity (lower fluidity) of the membranes isolated from smooth muscle cells from hypertensive as compared with those isolated from normotensive rats (p less than 0.01). Preincubation of membranes from hypertensive rats with 5 mM calcium reduced membrane microviscosity in "core" and in "surface" regions of the bilayer toward values observed in Wistar-Kyoto rats. Phospholipid composition did not differ between intact aortas and cultured mesenteric cells or between those tissues obtained from normotensive and from hypertensive rats. The total lipid-associated radioactivity was significantly lower in cells from stroke-prone spontaneously hypertensive rats than in those from Wistar-Kyoto controls (p less than 0.01). Phosphatidylcholine incorporated 70% and phosphatidylinositol 16% of total lipid-associated radioactivity, with no difference between cells from hypertensive and normotensive animals. Turnover of phosphatidylethanolamine was greater in cells from Wistar-Kyoto rats (p = 0.02), whereas turnover of phosphatidylserine was greater in cells from stroke-prone spontaneously hypertensive rats (p = 0.04). The greater microviscosity of the lipid bilayer in hypertension is a generalized defect of the matrix in which the transport proteins function. We hypothesize that this defect is responsible for the multiple abnormalities of membrane transport systems that have been described in genetic hypertension.

Because of the known influence of the lipid bilayer on membrane transport systems, the characteristics of the bilayer from vascular smooth muscle and from platelets were studied in genetically hypertensive and in normotensive rats. Membrane microviscosity was measured by the degree of polarization of embedded fluorophores. Both the core of the bilayer in which diphenylhexatriene (DPH) was embedded and the surface in which the trimethyl-ammonium derivative of DPH (TMA-DPH) was embedded evidence a greater microviscosity (less fluid) in the hypertensive than in the normotensive rat. We had previously observed that monovalent cation fluxes were elevated in hypertension. We now observe that an increase in calcium concentration reverses both the elevated microviscosity and the increased cation fluxes. Conversely an increased incorporation of cholesterol in the membrane increases both the microviscosity and the cation fluxes. We hypothesize that the greater microviscosity of the lipid bilayer in hypertension constitutes a generalized defect of the matrix in which the transport proteins function. We further hypothesize that this defect is responsible for the multiple abnormalities of membrane transport systems and the increase in vascular reactivity that have been described in genetic hypertension.

We examined mechanisms of relaxation in intact and endothelium-denuded thoracic aortic rings of rat in response to various concentrations of calcium (from 1.6 to 10.1 mM) after contraction induced by 30 mM KCl. The relaxation to calcium was concentration dependent in intact and denuded rings. This effect was greater in intact preparations than in denuded preparations or in intact preparations treated with methylene blue (10(-5) M). This indicates that the relaxation by calcium is partly mediated by releasing endothelium-derived relaxing factors (EDRFs). In the presence of A23187, the relaxation to calcium was attenuated in intact rings but not in denuded rings, whereas calcium relaxation was not significantly altered by sodium nitroprusside. These observations suggest that the calcium-induced relaxation is reduced if EDRF has already been released by A23187. We conclude that, paradoxically, the same increase in extracellular Ca2+ concentration that causes an increase in endothelial intracellular calcium concentration ([Ca2+]i) to produce EDRF also results in membrane stabilization of the vascular smooth muscle cell to decrease [Ca2+]i and cause relaxation. These two mechanisms are additive in producing calcium relaxation in the intact artery.

The vessel wall is thicker in hypertension. Folkow demonstrated that adaptive structural changes occur in vessels in response to the increased wall stress of hypertension. Because the vessel wall thickens and encroaches on the lumen, the adaptive change results in an elevated vascular resistance. It also exaggerates the vasoconstrictor effects of vascular smooth muscle contraction, thereby increasing vascular reactivity to physiologically occurring vasoactive agents. As solid as this information may be, important unanswered questions still remain related to the question "What makes the pressure go up in the first place?" In this brief review, we have examined possible culprits both in the area of extrinsic vascular regulatory systems and in that of intrinsic changes in the vascular smooth muscle cell. Interesting newly described vasoactive agents currently are being evaluated. On the other hand, generalized intrinsic abnormalities in the cell membrane are well documented in hypertension. Many individual transport systems display this abnormality, suggesting that the primary defect may be in the lipid bilayer that influences the function of all integral protein transport systems. Abnormalities also have been found in the cells' signal transduction systems, whereas the energy metabolism and contractile protein system are essentially normal. Functional abnormalities of the vascular smooth muscle cell in hypertension must explain both its increased contraction and its increased growth. It is likely that the same functional abnormality may explain both of these changes.

Vascular responses to ATP were studied in aortic rings isolated from stroke-prone spontaneously hypertensive rats (SHRSP) and normotensive Wistar-Kyoto rats (WKY). Low concentrations of ATP (10 nM to 10 microM) caused relaxation and high concentrations (0.1 mM to 10 mM) caused contraction. Both of these responses were accentuated by factors released from the endothelium. The endothelium-derived relaxing factor (EDRF) was blocked by NG-monomethyl-L-arginine (L-NMMA). This is the first time that it has been reported that ATP causes the release of an endothelium-derived contracting factor (EDCF). Its release was diminished but not completely blocked by cyclooxygenase inhibitors. Assays of muscle bath prostanoid composition indicated that ATP stimulation caused the release of prostaglandins I2 and E2 and thromboxane A2 from intact aortic rings. Evidence is presented that neither endothelin nor superoxide anion contributed to the EDCF. No difference was observed between WKY and SHRSP with regard to either the endothelial contributions to the response, or the direct action on vascular smooth muscle of ATP. High concentrations of ATP achieved intravascularly in hypoxia may cause vasospasm by release of endothelial prostanoids.

Eleven coarctation hypertensive (CH), twelve sham control (C), and seven one-kidney, one-clip (1K,1C) rats were used to examine the role of pressure and the endothelium in vascular sensitivity changes to acetylcholine (ACh), serotonin (5-HT), and norepinephrine (NE) in chronic arterial hypertension. Terminal mean carotid artery pressures were CH = 156 +/- 5 mmHg, C = 99 +/- 3 mmHg, and 1K,1C = 159 +/- 5 mmHg. Femoral artery pressures were CH = 100 +/- 3 mmHg, C = 98 +/- 4 mmHg, and 1K,1C = 154 +/- 4 mmHg, respectively. Isometric tension recordings were made from helically cut strips of thoracic and abdominal aortas, with and without functional endothelium, from the three groups of rats. Sensitivity to relaxation by acetylcholine, expressed as -log of 50% effective dose, was significantly depressed in thoracic aortas from CH and 1K,1C rats and abdominal aortas from 1K,1C rats but not from abdominal aortas of CH rats. A similar relationship between the groups was seen for 5-HT contractions. Sensitivity to NE was enhanced in thoracic and abdominal aortas of hypertensive rats. Inactivation of aortic endothelia abolished ACh responses, did not alter 5-HT relationships between the three groups, and abolished the differences in sensitivity to NE in thoracic aortas. The data suggest that pressure and the endothelium may play a role in vascular sensitivity changes in hypertension.

Several interventions are used to induce hypertension in the experimental animal. The three most used interventions are renal ischemia, mineralocorticoid excess, and genetic manipulation. The sequence of events leading from these initiating manipulations to the elevated arterial pressure is being explored to define the mechanism responsible for hypertension. The following mechanisms are currently extensively evaluated: Pressor and depressor factors of renal origin, neurogenic regulation, circulating humoral factors, vessel wall hypertrophy, and membrane transport abnormality. The experimental models of hypertension hold great promise in providing an understanding of the mechanisms and developing effective treatment in clinical hypertension.

Evidence has been presented that: 1.) Changes in lipid bilayer alter the function of integral membrane proteins. 2.) There is less calcium bound to the plasma membrane in hypertension. 3.) Structural and functional abnormalities of the lipid bilayer have been reported in genetic hypertension. We hypothesize that multiple abnormalities of membrane transport systems in hypertension are secondary to an inherent abnormality of the lipid bilayer in which these transport proteins reside.

The relation between endothelin and acetylcholine (ACh) was examined and compared in aortas from Wistar-Kyoto (WKY) rats and from stroke-prone spontaneously hypertensive rats (SHRSP). The relaxation produced by ACh in an endothelin-induced contraction was less in aortas from WKY rats than in those from SHRSP. In aortas from WKY rats but not in those from SHRSP, the contraction produced by endothelin was augmented when the intact aortic rings were treated with methylene blue (10(-5) M). This augmentation was also found in preparations of the WKY rat aortic rings in which the endothelium had been removed. The augmentation was not present in SHRSP aortic rings that had been similarly denuded. Treatment with indomethacin (5 x 10(-6) M) had no effect on endothelin-induced contraction in either WKY rat or SHRSP aortic rings. Our findings indicate that endothelin and ACh have in common the ability to release endothelium-derived relaxing factor (EDRF) in WKY rat aortic rings. The reduced endothelium-dependent relaxation in response to ACh in the WKY rat probably reflects the fact that endothelin had already released the EDRF in rings from this strain of rats. The release of EDRF by endothelin is less in SHRSP than it is in WKY rats. Because of this failure of endothelin to release EDRF in SHRSP, endothelin may contribute to the increase in total peripheral resistance in this form of hypertension.

In previous studies, we measured a greater intracellular free calcium concentration and net potassium efflux, possibly calcium activated, in lymphocytes from spontaneously hypertensive stroke-prone rats (SHRSP) as compared with Wistar-Kyoto (WKY) rats. In this study, we addressed two related questions: 1) Can the greater intralymphocytic calcium concentration of the SHRSP account for the greater net potassium efflux? 2) Is the calcium sensitivity of calcium-activated potassium channels in lymphocytes from SHRSP different as compared with that of those from WKY rats? Ionomycin, a calcium ionophore, caused a concentration-dependent and proportional increase in net potassium efflux and intracellular free calcium concentration in lymphocytes from both strains of rat. Based on the relations between net potassium efflux and intracellular free calcium concentration established with ionomycin, the resting net potassium efflux of lymphocytes from SHRSP is greater than would be predicted based on the resting intracellular free calcium concentration. Using the patch clamp technique, we were able to identify and characterize a calcium-activated potassium channel in the plasma membrane of lymphocytes from both strains of rat. Potassium currents were recorded that had a slope conductance of 18.1 +/- 1.49, n = 6, and 18.5 +/- 1.44, n = 7, in WKY rat and SHRSP thymocytes, respectively. The channel exhibited rectification of the outward current in both strains of rat. Channels tended to appear in clusters of two or more per patch and were recorded in 30-50% of the patches examined. Calcium sensitivity of the channels was similar; maximum activation occurred at 700 nM free calcium concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

The ability of the Na-Ca exchanger to modify vascular relaxation was studied in rings isolated from tail arteries of stroke-prone spontaneously hypertensive rats (SHRSP) and normotensive Wistar-Kyoto rats (WKY). The arteries were contracted with norepinephrine (NE) 1 microM and after stabilization they were transferred to a Ca-free physiological salt solution still in presence of NE. The time to 50% relaxation (T-50) in these conditions was significantly greater in SHRSP (78 +/- 7 s) than in WKY (50 +/- 7 s). When the calcium pump was stopped with vanadate (VAN), the Ca uptake by the sarcoplasmic reticulum with ryanodine (RY) and the Na-Ca exchanger with a Na-free PSS, the relaxation was slowed (T-50 increased to 198 +/- 16 s in SHRSP and to 162 +/- 14 s in WKY). Releasing the Na-Ca exchanger only (i.e. still with VAN and RY but with normal Na in the bath) the T-50 for relaxation in Ca-free PSS was, in WKY, nearly as fast as in control conditions (54 +/- 8 s). However, the Na-Ca exchanger in SHRSP was not so effective, and the T-50 for relaxation was slower than in control conditions (122 +/- 10 s). We conclude that the activity of the Na-Ca exchanger is depressed in tail arteries of SHRSP. This abnormality in resistance vessels, would contribute to the enhanced vascular tone present in hypertension.

We explored the hypothesis that postaglandin-induced vasodilation is caused by activation of the electrogenic sodium-potassium pump which results in membrane hyperpolarization and relaxation of vascular smooth muscle. Helical strips of rat tail artery relax in response to potassium after norepinephrine-induced contractions in physiological salt solution containing a low-potassium concentration. The amplitude of this potassium relaxation is used as an index of sodium-potassium ATPase activity. It was observed that PGA1, PGE2, and PGF2alpha (10(-6) g/ml) significantly enhanced the magnitut. PGE2 caused relaxation of contractions induced by either 25 mM KCl or norepinephrine (10(-9) g/ml), and these relaxations were inhibited by 10(-4) M ouabain. Indomethacin (5.3 x 10(-6) g/ml) and meclofenamate (10(-6) g/ml) reduced the magnitude of potassium-induced relaxation by more than 30% of control. PGF2alpha (10(-5) g/ml) reversed the inhibition of potassium relaxation by meclofenamate. These observations suggest that prostaglandins induce vascular smooth muscle relaxation by stimulation of the sodium pump and that endogenous prostaglandins normally potassium relaxation.

There is evidence that the relaxation of vascular smooth muscle produced by isoproterenol or cyclic AMP is mediated by membrane hyperpolarization. The current study investigates the possibility that this hyperpolarization, and hence the relaxation, may be produced by activation of the electrogenic sodium pump. Rat and pig tail artery strips were placed in a 1.0-mM potassium solution for 15 min. This procedure results in a decrease in the activity of the sodium pump. The strips were then made to contract in response to norepinephrine. Two minutes later, the concentration of potassium was increased to 6.0 mM and a relaxation occurred. The amplitude of this relaxation reflects the activity of the sodium pump. Either isoproterenol or dibutyryl-cyclic AMP causes an enhancement (time or degree) of potassium-induced relaxation. Theophylline potentiated potassium-induced relaxation in pig arteries but not in rat arteries. The relaxant action of isoproterenol on 1.0 mM barium contractures of rat arteries was inhibited by treatment with ouabain or with potassium-free solution. Ouabain inhibited the relaxant action of isoproterenol in pig arteries contracted with depolarizing potassium solution but not in rat tail arteries. Dibutyryl-cyclic AMP, theophylline and nitroprusside caused relaxation of serotonin-induced contractions; however, in rat arteries these responses were not inhibited by ouabain or by the absence of potassium. Similar studies on tail arteries from baboons, dogs, pigs and cats showed that relaxation by dibutyryl-cyclic AMP or by theophylline had some dependency on the activity of the sodium pump. These observations are consistent with the following conclusions: 1) isoproterenol and cyclic AMP potentiate the electrogenic pumping of sodium and potassium responsible for potassium-induced relaxation; 2) the relaxing action of isoproterenol, dibutyryl-cyclic AMP and theophylline are dependent upon experimental conditions and the species from which the vascular tissue is obtained; and 3) there is a component of isoproterenol- and cyclic AMP-induced relaxation which is not altered by inhibition of the electrogenic sodium pump in the rat.

Bleeding gastric ulcers were a major cause of morbidity and mortality in young swine subjected to surgery, chronic catheterization, and daily experimental manipulation. Some of the animals died suddenly due to exsanguination into the gastrointestinal tract, while others survived for several days following the onset of clinical signs. These signs included dark, tarry stools, lethargy, pale mucous membranes, decreased appetite, and dyspnea. Abnormal clinical laboratory findings included decreased hematocrit, hemoglobin and erythrocyte counts indicative of chronic blood loss anemia. On postmortem examination, single or multiple ulcers of variable sizes were found in the nonglandular cardiac portion of the stomach, and the gastrointestinal tract often contained blood. Histologically, the ulcers had a base of granulation tissue with surface suppuration. Prophylactic treatment of these ulcers was initiated using cimetidine, a histamine II blocker. The drug was administered via the drinking water at 15 mg/kg body weight/day. Fourteen of 62 (22.5%) pigs that did not receive cimetidine developed bleeding ulcers. Of 45 animals given daily prophylactic doses of cimetidine, none manifested clinical signs indicative of a bleeding ulcer. These results indicated that cimetidine was effective in preventing morbidity and mortality due to bleeding gastric ulcers in young swine used in chronic laboratory experiments.

Hypertension was induced in young male pigs by subcutaneous implantation of deoxycorticosterone acetate in a Silastic rubber carrier. Hemodynamic variables were periodically monitored. Six to eight weeks after implantation, the animals were necropsied and aortas were dissected. Glycosaminoglycans (GAG) were isolated from aortas from hypertensive pigs and from normotensive controls. Individual glycosaminoglycans in mixtures were fractionated and quantitated by chromatography on Dowex 1 Cl- column. No differences were noted in total glycosaminoglycan concentration between hypertensive and control animal aortas; the differences in individual GAG in aorta media-adventitia between the groups were not statistically significant. The relative proportions of heparan sulfate and dermatan sulfate in aorta intima were significantly greater (p less than 0.05) in hypertensive aortas than in normotensive intima. These two glycosaminoglycans increased in hypertensive animals at the expense of chondroitin 4-sulfate and hyaluronic acid. There was no difference in chondroitin 6-sulfate between the groups. A possible explanation of changes of glycosaminoglycans in hypertension because of altered lysosomal activity is suggested.

Extensive evidence reported here and elsewhere indicates a hormonal role for atrial natriuretic factor. In the light of this evidence, it appears that atrial natriuretic hormone is a more appropriate term for these peptides than atrial natriuretic factor. Plasma levels of immunoreactive atrial natriuretic hormone were measured daily in seven pigs before and 1 week after subcutaneous implantation of deoxycorticosterone acetate (DOCA). Nine other animals underwent daily measurements of mean arterial pressure and central venous pressure during similar treatments. Plasma immunoreactive atrial natriuretic hormone levels rose progressively during the first 3 days after implantation, from a basal level of 60 +/- 9 pmol/L to a peak level of 159 +/- 21 pmol/L (p less than 0.05), and they remained significantly elevated throughout the rest of the 7-day observation period. In two animals that were restudied 6 weeks after DOCA implantation, plasma immunoreactive atrial natriuretic hormone had returned to preimplantation levels. The rise in plasma hormone levels after DOCA implantation closely paralleled the previously reported time course of mineralocorticoid escape. Whether atrial natriuretic hormone plays an important part in the escape phenomenon remains to be determined.

Balances of sodium, potassium, and water were studied in the growing male pig as hypertension developed in response to subcutaneous implantation of deoxycorticosterone acetate (DOCA). Serum sodium, potassium, deoxycorticosterone (DOC), aldosterone, and plasma renin activity (PRA) were determined. These variables were observed in a total of 10 experimental and nine control pigs. All animals were uninephrectomized and fed a diet of Purina Pig Chow and tap water ad libitum. No salt was added to the food or water. Serum DOC levels rose dramatically on the day of the implantation, then gradually declined but remained approximately 10 times greater than control levels 40 days after implant. Plasma renin activity was suppressed rapidly and completely, whereas aldosterone fell only slowly to about half its control value. Sodium retention was maximum during the first 24 hours. Therefore an "escape" process became operative, causing sodium balance to return to normal after the third day, at which time the major rise in arterial pressure occurred. A marked increase in water turnover (intake and output) also began after the third day and persisted throughout the experimental period. Water balance remained normal during this period of increased turnover. Hypokalemia developed in the absence of kaliuresis, suggesting that potassium moved into the cells. Except for the potassium retention, these changes parallel the abnormalities seen in other states of mineralocorticoid excess.

Helical strips of rat tail artery were observed to relax in response to potassium after contraction induced by 10(-7) g/ml norepinephrine in potassium-free solution. After several minutes of relaxation, the strips showed an abrupt redevelopment of tension. The amplitude of the potassium-induced relaxation was employed as an index of the activity of the electrogenic sodium-potassium pump and hence of the Na+-K+ ATPase. This assumption seemed justified because the observed amplitude of potassium-induced relaxation paralleled known effects of the following variables on Na+-K+ ATPase: (1) intracellular sodium concentration; (2) ouabain administration; (3) magnesium; (4) temperature, and (5) potassium concentration. The relaxation that occurred in response to potassium is suggested to be due to an enhanced Na+-K+ ATPase resulting in increased electrogenic transport of sodium and potassium and, consequently, hyperpolarization. We propose that potassium-induced relaxation of rat tail artery may be used as a functional indicator of Na+-K+ ATPase activity in vascular smooth muscle.