Search

Aldosterone, in doses inappropriate to the salt status, plays an important role in the development of cardiovascular injury, including endothelial dysfunction, independent of its hypertensive effects. Acute non-genomic effects of aldosterone acting on mineralocorticoid receptors are inconsistent in healthy humans: vasoconstriction or forearm blood flow decrease via endothelial dysfunction, vasodilatation mediated by increased NO actions, or no effects. However, in studies with experimental animals, aldosterone mostly enhances vasodilatation mediated by endothelium-derived NO. Chronic exposure to aldosterone, which induces genomic responses, results in impairments of endothelial function through decreased NO synthesis and action in healthy individuals, experimental animals and isolated endothelial cells. Chronic aldosterone reduces NO release from isolated human endothelial cells only when extracellular sodium is raised. Oxidative stress is involved in the impairment of endothelial function by promoting NO degradation. Aldosterone liberates endothelin-1 (ET-1) from endothelial cells, which elicits ET(A) receptor-mediated vasoconstriction by inhibiting endothelial NO synthesis and action and through its own direct vasoconstrictor action. Ca(2+) flux through T-type Ca(2+) channels activates aldosterone synthesis and thus enhances unwanted effects of aldosterone on the endothelium. Mineralocorticoid receptor inhibitors, ET(A) receptor antagonists and T-type Ca(2) + channel blockers appear to diminish the pathophysiological participation of aldosterone in cardiovascular disease and exert beneficial actions on bioavailability of endothelium-derived NO, particularly in resistant hypertension and aldosteronism., (© 2012 The Authors. British Journal of Pharmacology © 2012 The British Pharmacological Society.)

Vascular endothelial dysfunction is regarded as a primary phenotypic expression of normal human aging. This senescence-induced disorder is the likely culprit underlying the increased cardiovascular and metabolic disease risks associated with aging. The rate of this age-dependent deterioration is largely influenced by the poor-quality lifestyle choice, such as smoking, sedentary daily life, chronic alcohol ingestion, high salt intake, unbalanced diet, and mental stress; and it is accelerated by cardiovascular and metabolic diseases. Although minimizing these detrimental factors is the best course of action, nonetheless chronological age steadily impairs endothelial function through reduced endothelial nitric oxide synthase (eNOS) expression/action, accelerated nitric oxide (NO) degradation, increased phosphodiesterase activity, inhibition of NOS activity by endogenous NOS inhibitors, increased production of reactive oxygen species, inflammatory reactions, decreased endothelial progenitor cell number and function, and impaired telomerase activity or telomere shortening. Endothelial dysfunction in regional vasculatures results in cerebral hypoperfusion triggering cognitive dysfunction and Alzheimer's disease, coronary artery insufficiency, penile erectile dysfunction, and circulatory failures in other organs and tissues. Possible prophylactic measures to minimize age-related endothelial dysfunction are also summarized in this review., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Mental stress is an important factor contributing to recognized mechanisms underlying cardiovascular events. Among these, stress-related endothelial dysfunction is an early risk factor that predicts future development of severe cardiovascular disorders. Acute mental stress by a variety of tests impairs endothelial function in humans, although the opposite results have been reported by some investigators. Chronic stress always deteriorates endothelial function in humans and experimental animals. Stress hormones, such as glucocorticoids and pro-inflammatory cytokines, and endothelin-1 liberated in response to mental stress participate in endothelial dysfunction possibly via downregulation of endothelial nitric oxide synthase (eNOS) expression, eNOS inactivation, decreased nitric oxide (NO) actions, and increased NO degradation, together with vasoconstriction counteracting against NO-induced vasodilatation. Catecholamines do not directly affect endothelial function but impair its function when blood pressure elevation by the amines is sustained. Endogenous opioids favorably affect endothelial function, which counteract deteriorating effects of other stress hormones and mediators. Inhibition of cortisol and endothelin-1 production, prevention of pro-inflammatory mediator accumulation, hypnotics, mirthful laughter, humor orientation, and lifestyle modification would contribute to the prevention and treatment for stress-related endothelial dysfunction and future serious cardiovascular disease.

Vasodilator substances liberated from endothelial cells, mainly nitric oxide (NO), play important roles in physiologically regulating blood flow and blood pressure and preventing pathological vascular damage. Impairment of these actions promotes the genesis of cardiovascular diseases such as hypertension, cerebral and cardiac hypoperfusion, impaired vasodilatation and atherosclerosis. Low concentrations of alcohol induce increased release of NO from the endothelium due to activation and expression of NO synthase (NOS). In contrast, administration of high concentrations of alcohol or its chronic ingestion impairs endothelial functions in association with reduced NO bioavailability. The endogenous NOS inhibitor asymmetric dimethylarginine may participate in decreased synthesis of NO. Chronic alcohol intake also impairs penile erectile function possibly by interfering with endothelial, but not nitrergic nerve, function. This review article summarizes the vascular actions of NO derived from endothelial and neuronal NOS as affected by alcohol, other than wine, and acetaldehyde in healthy individuals, human materials and various experimental animals.

We compared the mechanisms of vasorelaxation of acetylcholine and of substance P with reference to K(+) channels, and analyzed pharmacologically the nature of endothelium-derived substance(s) other than NO and prostanoids in monkey and dog coronary arteries. Coronary arteries were isolated from monkeys and dogs, and the isometric tension of the artery strips was measured. In canine coronary artery strips treated with indomethacin plus N(G)-nitro- L-arginine ( L-NA) and partially contracted with prostaglandin F(2alpha), acetylcholine induced concentration-related relaxation, which was abolished by removal of the endothelium. The relaxation was markedly suppressed but not abolished in the strips exposed to high K(+) media. Charybdotoxin plus apamin potently inhibited the relaxation to the similar extent to that by high K(+) media, whereas glibenclamide or iberiotoxin had no effect. The relaxation was markedly inhibited by quinacrine, a phospholipase A(2) inhibitor, and ketoconazole, a selective cytochrome P450 (CYP) 3A inhibitor, but not by sulfaphenazole, a selective CYP 2C inhibitor. In contrast to acetylcholine, endothelium-dependent and indomethacin-plus- L-NA-resistant relaxation induced by substance P was not inhibited by high K(+) media, charybdotoxin plus apamin, or ketoconazole. Quinacrine and AA861, a 5-lipoxygenase inhibitor, inhibited the relaxation induced by substance P. In monkey coronary artery, acetylcholine-induced relaxation resistant to indomethacin plus L-NA was abolished by endothelial denudation and by treatment with high K(+) media, charybdotoxin plus apamin, progesterone and ketoconazole, but was not affected by iberiotoxin or sulfaphenazole. Substance P did not relax monkey coronary arteries. It is concluded that endothelium-dependent, nitric oxide- and prostanoid-independent relaxation induced by acetylcholine in monkey and dog coronary arteries are mediated by charybdotoxin plus apamin-sensitive but iberiotoxin-insensitive Ca(2+)-activated K(+) channel opening substance(s), which may be CYP3A-derived arachidonic acid metabolite(s). Contrasting to the response to acetylcholine, endothelium-dependent, indomethacin-plus- L-NA-resistant relaxation induced by substance P in dog coronary artery is not associated with K(+) channel opening, and may be mediated by 5-lipoxygenase product(s).

Modifications by hyperlipidemia of endothelium-dependent and -independent relaxations were evaluated in cerebral and temporal arteries from control and hyperlipidemic (high cholesterol-fed) monkeys. Histologically atherosclerotic lesions were not observed in either group. Relaxations induced by histamine, abolished by N(G)-nitro->L-arginine (>L-NA), were significantly potentiated in the hyperlipidemic monkey cerebral arteries, compared with those in the arteries from control monkeys. Treatment with superoxide dismutase did not affect the histamine-induced relaxation. Conversely, endothelium-dependent relaxations induced by A23187, Ca2+ ionophore, in cerebral arteries did not differ between control and hyperlipidemic monkeys. In temporal arteries, relaxations by acetylcholine and A23187 did not differ between control and hyperlipidemic monkeys. Endothelium-dependent and -independent relaxations by adenosine diphosphate in cerebral and temporal arteries were not affected by hyperlipidemia. Endothelium-independent relaxations by exogenously applied nitric oxide did not differ in the arteries from control and hyperlipidemic monkeys. Nicotine-induced relaxations in cerebral arteries, which were mediated with nitric oxide released from nitroxidergic (nitrergic) nerves, and the contractions caused by nicotine in temporal and mesenteric arteries treated with >L-NA did not differ between control and hyperlipidemic monkeys. It is concluded that long exposure to hyperlipidemia did not affect endothelial functions of monkey middle cerebral and temporal arteries but enhanced nitric oxide-mediated relaxations caused by histamine, possibly due to upregulation of endothelial histamine receptor-mediated functions in the cerebral arteries. The nitroxidergic (nitrergic) and adrenergic nerve functions do not seem to be affected by hyperlipidemia.

The present study aimed to determine the action of angiotensin II and to pharmacologically analyze mechanisms of their action in isolated uterine arteries. Canine and human uterine artery strips were suspended in Ringer-Locke solutions for isometric tension recording. Canine and human uterine arteries responded to angiotensin II with transient contraction followed by relaxation, which were abolished by losartan, an AT1 receptor subtype antagonist. Cyclooxygenase inhibitors augmented the contraction and abolished the relaxation. The relaxation was also abolished or suppressed by tranylcypromine, a prostaglandin I2 synthesis inhibitor. The relaxant response of dog uterine arteries to angiotensin II was partially suppressed by endothelium denudation but was not influenced by nitric oxide synthase inhibitor. Conversely, the response of human uterine arteries to the peptide was unaffected by endothelium denudation. The antagonists used and endothelium denudation did not inhibit the relaxation caused by a prostaglandin I2 analogue. It appears that the angiotensin II-induced relaxation is mediated by vasodilator prostaglandins, possibly prostaglandin I2, released from both endothelium and subendothelial tissues in dog uterine arteries. In human uterine arteries, the vasodilator prostaglandin is released from subendothelial tissues due to AT1 receptor stimulation by the peptide.

We have reported that a deficiency of tetrahydrobiopterin (BH(4)), an active cofactor of endothelial NO synthase (eNOS), contributes to the endothelial dysfunction through reduced eNOS activity and increased superoxide anion (O(2)(-)) generation in the insulin-resistant state. To further confirm this hypothesis, we investigated the effects of dietary treatment with BH(4) on endothelium-dependent arterial relaxation and vascular oxidative stress in the aortas of insulin-resistant rats. Oral supplementation of BH(4) (10 mg. kg(-1). d(-1)) for 8 weeks significantly increased the BH(4) content in cardiovascular tissues of rats fed high levels of fructose (fructose-fed rats). Impairment of endothelium-dependent arterial relaxation in the aortic strips of the fructose-fed rats was reversed with BH(4) treatment. The BH(4) treatment was associated with a 2-fold increase in eNOS activity as well as a 70% reduction in endothelial O(2)(-) production compared with those in fructose-fed rats. The BH(4) treatment also partially improved the insulin sensitivity and blood pressure, as well as the serum triglyceride concentration, in the fructose-fed rats. Moreover, BH(4) treatment of the fructose-fed rats markedly reduced the lipid peroxide content of both aortic and cardiac tissues and inhibited the activation of 2 redox-sensitive transcription factors, nuclear factor-kappaB and activating protein-1, which were increased in fructose-fed rats. The BH(4) treatment of control rats did not have any significant effects on these parameters. These results indicate that BH(4) augmentation is essential for the restoration of eNOS function and the reduction of vascular oxidative stress in insulin-resistant rats.

Mechanical responses to superoxide anion scavengers and nitric oxide (NO) synthase inhibitors in aortic endothelial cells were compared in normal chow-fed rats and those made insulin-resistant by feeding of fructose. Cu(2+), Zn(2+)-superoxide dismutase-induced vascular relaxation and superoxide production, measured by the lucigenin-enhanced chemiluminescence method, were greater in aortas from fructose-fed rats than in those from normal chow-fed rats. N(G)-nitro-L-arginine-induced contractions due to suppression of NO synthase activity were smaller in aortas from fructose-fed rats. Vascular mechanical responses may reflect the generation of superoxide and NO by the endothelium. Thus, isometric tension studies may be a useful tool for evaluating the production of these radicals in blood vessels.

To investigate underlying mechanisms responsible for the impaired nitric oxide (NO)-dependent vascular relaxation in the insulin-resistant state, we examined production of both NO and superoxide anion radical (O2-) and those modulating factors in aortas obtained from normal (CTR), insulin-treated (INS), or high fructose-fed (FR) rats. FR rats showed insulin resistance with endogenous hyperinsulinemia, whereas INS rats showed normal insulin sensitivity. Only FR aortic strips with endothelium elicited impaired relaxation in response to either acetylcholine or calcium ionophore A23187. Endothelial NO synthase (eNOS) activity and its mRNA levels were increased only in vessels from INS rats (P < 0.001), whereas eNOS activity in FR rats was decreased by 58% (P < 0.05) when compared with CTR rats. NO production from aortic strips stimulated with A23187 was significantly lower in FR than CTR rats. In contrast, A23187-stimulated O2- production was higher (P < 0.01) in FR than CTR rats. These differences were abolished when aortic strips were preincubated in the media including (6R)-5,6,7,8-tetrahydrobiopterin (BH4), an active cofactor for eNOS. Furthermore, as compared with CTR rats, aortic BH4 contents in FR rats were decreased (P < 0.001), whereas the levels of 7,8-dihydrobiopterin, the oxidized form of BH4, were increased, with opposite results in INS rats. These results indicate that insulin resistance rather than hyperinsulinemia itself may be a pathogenic factor for decreased vascular relaxation through impaired eNOS activity and increased oxidative breakdown of NO due to enhanced formation of O2- (NO/O2- imbalance), which are caused by relative deficiency of BH4 in vascular endothelial cells.

Impairment of nitric oxide-dependent vascular relaxation is a characteristic feature of the insulin-resistant state. To understand those mechanisms, we examined imbalance of O2-/NO production in aortic endothelial cells obtained from high fructose-fed, exogenous hyperinsulinemic, and control rats. Aortic segments from both high fructose-fed and insulin-treated rats produced a 4-fold more O2- than control rats evaluated by a chemiluminescence method. The O2- production in the aortas of both high fructose-fed and insulin-treated rats was mediated through activation of NADH/NADPH oxidase. In isometric tension studies, high fructose vessels with endothelium elicited impaired relaxation in response to acetylcholine or a calcium ionophore A23187 when compared with control rats, whereas these impaired vascular responses were not found in insulin-treated rats. Furthermore, endothelial constitutive NO synthase activity was increased in vessels from insulin-treated rats, but decreased in vessels from high fructose-fed rats. These results indicate that relative excess of O2- production through activation of NADH/NADPH oxidase over NO generation in endothelial cells may contribute to impaired endothelial-dependent relaxation in insulin-resistant state.

Canine retinal central arterial strips responded to acetylcholine with a relaxation that was endothelium-independent. Indomethacin and atropine abolished the relaxation at low doses (10(-7) to 10(-6) M) and moderately attenuated the response to high concentrations (10(-5) and 10(-4) M). The residual relaxation at 10(-5) and 10(-4) M in indomethacin-treated strips were abolished by NG-nitro-L-arginine, hexamethonium, oxyhemoglobin and methylene blue, and the NG-nitro-L-arginine-induced inhibition was reversed by L-arginine. Cerebral arterial strips with endothelium responded to acetylcholine with a transient relaxation followed by a contraction, whereas only a relaxation was induced when endothelium was denuded. The relaxations at low and high doses were modified by atropine, indomethacin, hexamethonium and NG-nitro-L-arginine quite similarly to those seen in retinal arteries. Histochemical study demonstrated the presence of perivascular nerves containing NADPH diaphorase in whole mount preparations of the retinal artery. It is concluded that acetylcholine-induced retinal arterial relaxations, independent of endothelium, are mediated possibly by prostaglandin I2 in activation of muscarinic receptors and by nitric oxide derived from perivascular nerves in response to nicotinic receptor stimulation. On the other hand, vasoconstrictor prostanoids appear to be liberated from the endothelium by muscarinic receptor stimulation in cerebral arteries, and mechanisms underlying the relaxation are similar to those seen in retinal arteries.

1. In helical strips of dog superficial temporal arteries with intact endothelium, substance P elicited a concentration-related relaxation with an EC50 of 2.8 (2.4-3.2) x 10(-10) M. 2. The relaxant response to the peptide in low concentrations (1-4 x 10(-10) M) sufficient to produce approximately half maximal relaxation was not inhibited by indomethacin, but was markedly suppressed by NG-nitro-L-arginine (L-NOARG), a nitric oxide (NO) synthase inhibitor, and by endothelium denudation. 3. High concentration (10(-7) M) of substance P produced marked relaxations in endothelium-intact strips. Removal of the endothelium attenuated the relaxation, and indomethacin or tranylcypromine suppressed the endothelium-independent relaxation. In indomethacin-treated strips with intact endothelium, L-NOARG attenuated but did not abolish the relaxation. The residual, L-NOARG-resistant relaxation was not significantly inhibited by ouabain, glibenclamide or tetraethylammonium. 4. Substance P (10(-7) M) increased the levels of cyclic GMP and cyclic AMP. The increase in cyclic GMP was abolished by endothelium denudation and treatment with L-NOARG, whereas the cyclic AMP increment was abolished by indomethacin. 5. Three different mechanisms may be involved in the substance P-induced relaxation: (1) an endothelium-dependent relaxation mediated by the release of NO from the endothelium, resulting in an increase of cyclic GMP (low and high concentrations of the peptide); (2) an endothelium-independent relaxation in association with cyclic AMP increment caused by prostaglandin I2 released from subendothelial tissues (high concentration), and (3) another endothelium-dependent relaxation possibly mediated by unidentified mediator(s) released from the endothelium (high concentration).

Background and Purpose: Oxyhemoglobin is a key substance in provoking cerebral vasospasm and a scavenger of nitric oxide. The present study was designed to determine whether suppression of the action of endothelium-derived nitric oxide is involved in oxyhemoglobin-induced cerebroarterial contraction., Methods: Dog and monkey cerebral artery strips with and without endothelium were immersed for isometric tension recording in modified Ringer-Locke solution aerated with 95% oxygen and 5% carbon dioxide., Results: NG-nitro-L-arginine, a nitric oxide synthase inhibitor, produced concentration-related contraction that was greater in the strips with intact endothelium than in those denuded of endothelium. The D-enantiomer caused no or only a slight contraction. In the presence of NG-nitro-L-arginine, oxyhemoglobin elicited additional contraction that is comparable to or even greater than that obtained in the absence of the inhibitor. The oxyhemoglobin-induced contraction was attenuated by endothelium denudation., Conclusions: Inhibition of the basal release of nitric oxide from endothelium results in dog and monkey cerebral arterial contraction. However, the inhibition of nitric oxide action is not a major mechanism involved in oxyhemoglobin-induced contraction; other mechanisms, such as the release of prostanoids, appear to be important.

The endothelium-dependency of vasodilator responses was compared in helical strips of canine internal thoracic (ITA) and coronary arteries partially contracted with serotonin. The addition of acetylcholine produced a concentration-related relaxation in ITA and coronary arterial strips with an intact endothelium. The relaxations were not influenced by indomethacin, but were markedly inhibited or abolished by methylene blue, NG-nitro-L-arginine (L-NA), a nitric oxide (NO) synthase inhibitor, and endothelial denudation. The responses to low concentrations of acetylcholine were significantly greater in ITA than in coronary arteries, whereas relaxations induced by substance P, Ca2+ ionophore (A23187) or NO in ITA were significantly less. The substance P-induced relaxation in ITA and coronary arteries was endothelium-dependent, and it was almost abolished by L-NA. Relaxations induced by ATP in ITA were abolished by endothelium denudation and treatment with L-NA. In the coronary arteries, relaxing responses were inhibited only partially by removal of endothelium and L-NA. Acetylcholine, ATP and substance P relax canine ITA possibly by a mediation of endothelium-derived NO, but not prostaglandin I2. Coronary arterial relaxations induced by ATP appear to be mediated by an indirect action via NO released from the endothelium, in addition to a direct action on the smooth muscle.

Purposes of this study were to determine whether: (1) nitric oxide is involved in endothelium-dependent relaxation in helical strips of dog cerebral arteries; (2) relaxing factor distinct from NO is also involved, and (3) susceptibility to NG-nitro-L-arginine (L-NA), an NO synthase inhibitor, of the response to mediators liberating NO from the endothelium and nerve differs. Changes in isometric tension were recorded. In the strips contracted with prostaglandin F2 alpha, substance P and arginine vasopressin produced a relaxation which was abolished or reversed to a contraction by endothelium denudation. The relaxations were not influenced by indomethacin but were suppressed dose-dependently by L-NA, as was the response to nicotine that stimulates the non-adrenergic, non-cholinergic vasodilator nerve and liberates NO. The inhibitions were reversed by L- but not D-arginine. NO (acidified NaNO2)-induced relaxations were not reduced by L-NA. The inhibitory effect was greater in the responses to vasopressin than substance P; however, there was no significant difference in the response to nicotine vs. the peptides. Substance P increased the level of cyclic guanosine monophosphate (GMP) in the artery strips with the intact endothelium, the effect being abolished by endothelium denudation, L-NA and oxyhemoglobin. Relaxations caused by adenosine triphosphate (ATP) and adenosine diphosphate (ADP) were dependent partially on the endothelium. Treatment with L-NA attenuated the ATP-induced relaxation in the strips with endothelium but did not alter the response of denuded strips.(ABSTRACT TRUNCATED AT 250 WORDS)

In isolated porcine coronary arteries, acetylcholine elicited contractions that were potentiated by endothelium denudation. In endothelium-intact strips, the contraction deteriorated by repeated trials and was reversed to a relaxation. NG-nitro-L-arginine (L-NA), a nitric oxide (NO) synthesis inhibitor, abolished the relaxation or reversed it to a contraction. Endothelium-dependent relaxations caused by serotonin were also reversed to a contraction by treatment with L-NA. Relaxations caused by substance P were dependent on the endothelium and were abolished by oxyhemoglobin; however, L-NA did not completely abolish the relaxation. It may be concluded that porcine coronary arteries respond to acetylcholine with contractions by a direct action on smooth muscle that are minimized by stimulated release of NO from the endothelium. It appears that the relaxation caused by serotonin is due to NO released from the endothelium, whereas the substance P-induced relaxation is associated mainly with endothelium-derived NO produced by NO synthase sensitive to L-NA and also with NO produced via a L-NA-resistant process or via a pathway distinct from that through NO synthase.

Monkey cerebral artery strips partially contracted with prostaglandin F2 alpha responded to histamine with biphasic patterns of relaxation. The delayed and sustained relaxation was suppressed by cimetidine, whereas the phasic response was abolished by treatment with chlorpheniramine and NG-nitro-L-arginine (L-NA), a nitric oxide (NO) synthase inhibitor. The inhibition by L-NA was reversed by L-arginine. D-NA was without effect. Endothelium denudation abolished the phasic relaxation. We hypothesized that endothelium-dependent, phasic relaxations caused by histamine are mediated by NO that is released by H1-receptor stimulation, whereas the sustained relaxation is associated with the activation of H2-receptors in the smooth muscle of monkey cerebral arteries.

Effects of selective (nicardipine) and nonselective (Cd++) Ca++ channel antagonists on the responses of isolated dog cerebral arteries to vasodilator nerve stimulation, substance P, serotonin and prostaglandin F2 alpha were investigated; the relaxation caused by the nerve stimulation and the peptide is mediated by NO, possibly from the nerve and endothelium, respectively. Relaxant responses to nerve stimulation by electrical pulses and nicotine in the endothelium-denuded arteries were attenuated by Cd++, but not influenced by nicardipine; the concentrations of these antagonists were sufficient to suppress contractions caused by prostaglandin F2 alpha and serotonin to a similar extent. Increase in cyclic GMP by nicotine was also suppressed solely by Cd++. In the endothelium-intact arteries treated with indomethacin, relaxations induced by substance P were not affected by nicardipine, but were significantly attenuated by Cd++. The peptide-induced increase in cyclic GMP was suppressed by Cd++, but not by nicardipine. It is concluded that functional properties of the Ca++ channel responsible for increasing cytosolic Ca++ in the nerve and endothelium for the synthesis and release of nitric oxide or endothelium-derived relaxing factor differ from those of the channel in smooth muscle. Because Ca++ is a prerequisite for the synthesis of NO, smooth muscle does not appear to be the site of production of NO that transmits vasodilator information from the nerve or endothelium to cerebroarterial smooth muscle.

Objective: The existence and localization of renin in situ was examined in human arteries under non-pathological conditions., Design: Biochemical and immunohistochemical procedures were adopted to examine the existence of renin in human gastroepiploic arteries using an antibody raised against human recombinant renin or a specific renin inhibitor., Methods: (1) Renin activity (angiotensin I generating activity sensitive to antihuman recombinant renin antibody or a specific renin inhibitor) in the homogenate of human gastroepiploic arteries with and without endothelium was compared; (2) vascular renin was immunohistochemically stained using a modified avidin-biotin-peroxidase complex method., Results: (1) Renin activity in human gastroepiploic arteries with endothelium was significantly higher than in those without endothelium; (2) immunoreactive staining selectively occurred in the endothelial cells of human gastroepiploic arteries., Conclusions: Renin is present in endothelial cells of human arteries under non-pathological conditions. Endothelial renin may play a role in the control of vascular tone through local production of angiotensin II.

1. Endothelium-dependency of vasodilator responses was compared in helical strips of monkey cerebral and superficial temporal arteries contracted with prostaglandin F2 alpha. Acetylcholine produced an endothelium-dependent relaxation in the temporal arteries, but did not consistently alter the tone of cerebral arteries. 2. Adenosine 5'-triphosphate (ATP) produced a transient contraction followed by a relaxation in the temporal and cerebral arteries; removal of the endothelium partially attenuated the relaxation of the cerebral arteries and markedly suppressed the relaxation in the temporal arteries. The dependency of adenosine 5'-diphosphate (ADP)-induced relaxations on the endothelium was also greater in temporal arteries than in cerebral arteries. 3. Histamine-induced relaxations in the temporal arteries were independent of the endothelium and were reversed to contractions by cimetidine. Cerebral arterial relaxations induced by histamine were partly dependent on the endothelium. Relaxations caused by substance P were reversed to contractions by removal of the endothelium in the temporal arteries, whereas the peptide did not consistently alter the tone of cerebral arteries. 4. The Ca2+ ionophore, A23187, relaxed the temporal and cerebral arteries to a similar extent; removal of the endothelium abolished these relaxations. Glyceryl trinitrate elicited similar relaxation of cerebral and temporal arteries, and these were independent of the endothelium. 5. These findings clearly indicate heterogeneity in the endothelium-dependency of several vasodilator responses in monkey intra- and extracranial arteries, although the ability of these arteries to respond to A23187 and glyceryl trinitrate does not appear to differ. The heterogeneous responses observed so far could therefore be due to different distributions of receptors or to variation in receptor-effector coupling in endothelial cells.

In epicardial conduit coronary artery strips obtained during autopsy within 2.5 h after death, relaxations induced by low concentrations of histamine were reversed to contractions by removal of endothelium, whereas those caused by bradykinin, substance P, and Ca2+ ionophore A23187 were almost abolished. In the artery strips with intact endothelium, which responded to histamine, bradykinin, and substance P with moderate or marked relaxations, acetylcholine elicited contractions. Endothelium denudation failed to potentiate the contractile response to acetylcholine and serotonin. Relaxant responses to histamine, bradykinin, and substance P did not significantly differ in coronary arteries from adults (35-48 yr old) and seniors (63-82 yr old). Two strips from a 2-mo-old male responded to acetylcholine only with contractions, and their responses to the vasodilators were not greater than those seen in the adult and senior arteries. Histamine increased guanosine 3',5'-cyclic monophosphate (cGMP); the increments did not differ in the arteries from adults and seniors. It may be concluded that endothelium is a major site for relaxant actions of histamine, bradykinin, and substance P, whereas muscarinic receptors, if any, in endothelium do not play an important role in the generation of relaxing factor from human coronary arteries. The endothelium-dependent relaxations do not appear to be altered with increasing age or in the arteries with slight atherosclerotic changes.

Acetylcholine and substance P applied to the donor tissue, dog femoral artery segments with endothelium, produced moderate relaxations of the assay tissue, endothelium-denuded dog coronary artery strips. The relaxation was attenuated markedly by treatment of the assay tissue with hydroquinone and abolished by oxyhemoglobin or methylene blue. In this bioassay system, the effect of AA861 and TMK777, new 5-lipoxygenase inhibitors, was evaluated. When the donor tissue was treated with AA861 or TMK777, the responses to acetylcholine and substance P were attenuated moderately, whereas the relaxation by nitroglycerin was not influenced by AA861. However, the inhibitors when infused just below the donor tissue did not attenuate relaxant responses to acetylcholine and substance P. Application of superoxide dismutase (SOD) to the donor tissue caused a relaxation of the assay tissue, and potentiated the relaxation by acetylcholine and substance P. AA861 and TMK777 suppressed the relaxant responses to acetylcholine and substance P, respectively, in the presence and absence of SOD to a similar extent and abolished the SOD-induced relaxation. Pyrogallol abolished the relaxation by acetylcholine, but did not inhibit the response when the donor tissue was pretreated with SOD. Therefore, it appears that AA861 and TMK777 do not degrade endothelium-derived relaxing factor (EDRF) in the perfusate via generation of superoxide anion or block the action of EDRF on vascular smooth muscle, but interfere with the synthesis and/or release of EDRF. The findings obtained so far support the idea that lipoxygenase products participate in the generation of EDRF.

The addition of prostaglandin (PG) H2 produced a transient contraction followed by a relaxation in helical strips of dog cerebral arteries partially contracted with PGF2 alpha or K+. The contraction was abolished by removal of endothelium, and the relaxation was potentiated. Relaxation induced by PGI2 was not influenced by endothelium denudation. The PGH2-induced contraction in strips with intact endothelium was not influenced by OKY-046, a thromboxane A2 synthesis inhibitor, but was abolished by treatment with ONO3708, an antagonist of vasoconstrictor PGs, whereas the relaxation was inhibited by tranylcypromine or diphloretin phosphate, a nonselective PG antagonist. Contraction induced by arachidonic acid (AA) was reversed to relaxation by removal of endothelium or treatment with ONO3708. Treatment with indomethacin attenuated the AA-induced contraction in the intact strips and also the relaxation in the strips treated with ONO3708 or denuded of endothelium. It may be concluded that vasoconstrictor PGs are synthesized from PGH2 or AA mainly in endothelium, and the production of PGI2 from PGH2 is not dependent on endothelium. Thromboxane A2 in concentrations sufficient to elicit significant contractions does not appear to be liberated from the cerebroarterial wall stimulated by PGH2.

We compared responses to calcium ionophore A23187, vasopressin, and substance P in helical strips of dog middle cerebral, basilar, and posterior communicating arteries to obtain a better understanding of humoral control of cerebrovascular tone in different brain regions and its potential impact on mechanisms of cerebral vasospasm. A23187 relaxed these different arterial strips partially precontracted with prostaglandin F2 alpha to a similar extent. Vasopressin produced concentration-dependent relaxation in basilar and posterior communicating arterial strips, whereas middle cerebral arterial strips either contracted or relaxed slightly. Relaxations induced by A23187 and vasopressin were either abolished or converted to contractions by removal of the endothelium. In contrast, the relaxation of cerebral arterial strips to substance P was markedly attenuated but not abolished by endothelium denudation; the remaining relaxation was suppressed by indomethacin. In some cerebral arterial strips with intact endothelium, substance P caused a transient contraction that was reversed to a relaxation by indomethacin or ONO-3708, a prostaglandin antagonist. In arterial strips denuded of endothelium from the same dogs, substance P always produced relaxations. Relaxations of cerebral arterial strips to A23187 and vasopressin appear to be mediated by endothelium-derived relaxing factor. The function of vasopressin receptors in endothelial cells differs markedly in basilar and posterior communicating arteries versus middle cerebral arteries. Substance P-induced relaxations appear to be primarily associated with endothelium-derived relaxing factor and with prostaglandin I2, whereas contractions appear to be mediated by endothelium-derived prostaglandins.

In helical strips of monkey coronary and mesenteric arteries and dog mesenteric arteries partially contracted with prostaglandin (PG)F2 alpha, the mechanism of action of acetylcholine (ACh) has been analyzed by the use of pharmacological antagonists and by the endothelium-derived relaxing factor (EDRF) bioassay and the 6-keto PGF1 alpha radioimmunoassay. In conclusion, ACh releases vasodilator substance(s) from endothelium (EDRF) and also PGs from subendothelial tissues. Vasoconstrictor PGs appear to counteract the dilator action of EDRF in monkey coronary arteries, whereas vasodilator PG, possibly PGI2, appears to facilitate the relaxation caused by EDRF in monkey and dog mesenteric arteries.

The study presented so far demonstrates that there is a heterogeneity in the mechanisms of vasodilator action of BK in various dog blood vessels (coronary vs mesenteric artery, and mesenteric artery vs vein). The different mechanisms underlying the BK-induced vasodilatation are summarized in Fig. 3. Three mechanisms are at least involved; 1) EDRF-release from endothelial cells which may not be mediated by B1 receptor, but presumably by B2 receptor, 2) PGI2-release from endothelial cells, 3) PGI2-release from smooth muscle (subendothelial) cells. The PGI2-release may be mediated by B1 receptor. Vasodilatation caused by BK is mediated via "1" in coronary arteries, "2" + "3" in mesenteric veins, and "1" + "2" + "3" in mesenteric and renal arteries in the dog. Another reasons for the differences in the BK-induced vasodilatation may be different number or sensitivity of BK receptors located on the endothelial and smooth muscle cells, or the responsiveness of the vascular smooth muscle cells to the intermediate vasodilator substances and BK itself.

Prostaglandin (PG) H2 produced a transient contraction followed by a relaxation in helical strips of dog coronary, mesenteric and renal arteries contracted with PGF2 alpha. The contraction was in the order of mesenteric greater than renal greater than coronary artery. Removal of endothelium abolished the contraction in these arteries and significantly potentiated the relaxation only in mesenteric arteries. The relaxation was greater in mesenteric arteries than in renal and coronary arteries, denuded of endothelium. PGI2-induced relaxations were not influenced by endothelium denudation. In the arteries contracted with K+, PGH2-induced relaxations were attenuated, compared to those contracted with PGF2 alpha. Treatment with ONO3708, an antagonist of vasoconstrictor PGs, abolished the PGH2-induced contraction and potentiated the relaxation in the K+-contracted arteries. The relaxant response was suppressed by diphloretin phosphate, a PG receptor antagonist, as was the response to PGI2. PGH2-induced contractions in dog coronary, mesenteric and renal arteries would be due to vasoconstrictor PGs produced preferentially in the endothelium. However, production of PGI2 from PGH2 in endothelial and subendothelial tissues do not appear to differ.