Central role of connexin40 in the propagation of electrically activated vasodilation in mouse cremasteric arterioles in vivo

When a short segment of arteriole is stimulated, vasomotor responses spread bidirectionally along the vessel axis purportedly via gap junctions. We used connexin40 knockout (Cx40-/-) mice to study vasomotor responses induced by 10-second trains of electrical stimulation (30 Hz, 1 ms, 30 to 50 V) in 2nd or 3rd order arterioles of the cremaster muscle. Measurements were made at the stimulation site (local) and at conducted sites (500, 1000, and 2000 microm upstream). In wild-type (Cx40+/+) animals, electrical stimulation evoked a local vasoconstriction and a conducted vasodilation that spread very rapidly along the vessel length without detectable decay. In Cx40-/- mice, the conducted dilation was converted into either vasoconstriction or a slowly developing vasodilation that decayed along the vessel length. Tetrodotoxin (TTX, 1 micromol/L) had no effect on the local vasoconstriction in either Cx40+/+ or Cx40-/- mice, but enhanced the conducted vasodilation in Cx40+/+ animals. In Cx40-/- mice, TTX abolished the conducted vasoconstriction when present and revealed a small vasodilation that decayed with distance. In the group of Cx40-/- mice in which electrical stimulation elicited a conducted vasodilation, TTX had no effect. Immunocytochemistry revealed Cx40 only in the endothelial layer of arterioles from Cx40+/+ mice and complete elimination of this connexin in the Cx40-/- animals. These results indicate that focal current stimulation causes vasoconstriction by a combination of perivascular nerve stimulation and smooth muscle activation. Moreover, electrical stimulation activates a nonneuronal, Cx40-dependent vasodilator response that spreads along the vessel length without decay.     

Alpha- and beta-adrenergic mechanisms mediate blood pressure control by norepinephrine and angiotensin in ducks

Adrenergic mechanisms for the pressor actions of blood-borne L-norepinephrine (NE) and fowl angiotensin II (ANG II) were studied in barbiturate-anesthetized adult ducks (Anas platyrhynchos). NE (1.5-6.0 nmol X kg-1) or ANG II (0.4-1.6 nmol X kg-1) injected iv caused dose-dependent increases in mean arterial pressure (Pa) and pulse pressure (Pp) but slowed cardiac frequency (fH); higher doses of ANG II increased Pa, Pp, and fH X beta-Adrenergic blockade by propranolol lowered baseline Pa, completely blocked cardiovascular responses to isoproterenol, augmented the bradycardic effect of NE, and inhibited the stimulation of Pp by ANG II. However, the tachycardiac effect of high-dose ANG II persisted during beta-blockade. alpha-Adrenergic blockade following iv prazosin completely blocked the pressor effect of methoxamine, diminished the pressure response to NE, and decreased Pa sensitivity to ANG II injections. Combined alpha- and beta-adrenergic blockade decreased both the sensitivity and the maximal Pa response to ANG II. We conclude that (i) beta-adrenergic mechanisms predominate in the maintenance of resting Pa, (ii) NE increases Pa principally by alpha-adrenergic action while beta-adrenergic stimulation buffers the consequent bradycardia, and (iii) although the positive chronotropic effect of high doses of ANG II probably is not mediated by catecholamines, low doses of ANG II elevate Pa and Pp by alpha- and beta-adrenergic mechanisms.     

Renin–Angiotensin System Modulates Neurotransmitters in the Paraventricular Nucleus and Contributes to Angiotensin II-Induced Hypertensive Response

Angiotensin II (ANG II)-induced inflammatory and oxidative stress responses contribute to the pathogenesis of hypertension. In this study, we determined whether renin–angiotensin system (RAS) activation in the hypothalamic paraventricular nucleus (PVN) contributes to the ANG II-induced hypertensive response via interaction with neurotransmitters in the PVN. Rats underwent subcutaneous infusion of ANG II or saline for 4 weeks. These rats were treated for 4 weeks through bilateral PVN infusion with either vehicle or losartan (LOS), an angiotensin II type 1 receptor (AT1-R) antagonist, via osmotic minipump. ANG II infusion resulted in higher levels of glutamate, norepinephrine (NE), AT1-R and pro-inflammatory cytokines (PIC), and lower level of gamma-aminobutyric acid (GABA) in the PVN. Rats receiving ANG II also had higher levels of mean arterial pressure, plasma PIC, NE and aldosterone than control animals. PVN treatment with LOS attenuated these ANG II-induced hypertensive responses. In conclusion, these findings suggest that the RAS activation in the PVN contributes to the ANG II-induced hypertensive response via interaction with PIC and neurotransmitters (glutamate, NE and GABA) in the PVN.     

Mesenteric vasodilator responses in cirrhotic rats: A role for nitric oxide

The contribution of nitric oxide to mesenteric arterial vasodilator responses was investigated in the isolated perfused mesenteric arterial bed of cirrhotic rats (carbon tetrachloride/phenobarbitone; n = 6). Age- matched (n = 9) and phenobarbitone-treated rats (n = 9) served as controls. Responses to the endothelium-dependent dilators acetylcholine and adenosine 5'-triphosphate (ATP) and the smooth muscle dilator (NO donor) sodium nitroprusside were investigated after tone was raised by continuous infusion of methoxamine, before and during infusion of the NO synthesis inhibitor N^G-nitro-L-arginine methyl ester (L-NAME; 30 mumol/L) +/- L-arginine (1 mmol/L). A significant hyporesponsiveness to methoxamine infusion in cirrhotic preparations (P < .05) was not fully corrected by L-NAME. There was no difference in the percentage vasodilator response to acetylcholine in the cirrhotic group compared with controls; L-NAME significantly and reversibly inhibited the dilator response in all groups. ATP elicited dose-dependent vasodilation that, in the absence of L-NAME, did not differ between the groups. By contrast, in the presence of L-NAME, ATP (5 x 10^-8 mol) produced pronounced, reversible vasoconstriction only in cirrhotic animals (P < .02). Vasodilatation attributable to sodium nitroprusside (5 x 10^-8 mol) was significantly attenuated in cirrhotic rats. The methoxamine data support the concept of mesenteric hyposensitivity to vasoconstrictor agents in cirrhosis that may be at least partly NO mediated. Increased NO activity in smooth muscle leading to decreased guanylate cyclase availability may account for the diminished vasodilator responses to sodium nitroprusside in cirrhotic preparations. The unchanged responsiveness to vasodilatation by acetylcholine (ACh) and the vasoconstriction to ATP observed during NO blockade in cirrhotic animals indicate that mesenteric endothelial NO is unchanged or possibly diminished. (Hepatology 1996 Jan;23(1):130-6)     

Influence of angiotensin I on angiogenesis in vitro in the rat

The regulation of angiogenesis involves complex interactions. The aim of our study was to assess the influence of angiotensin II (ANG II) on different vascular beds in rat. Aortic, renal and mesenteric rings from 10 male Sprague-Dawley rats were cultured using a three-dimensional culture system consisting of rat type I collagen lattice. We assessed the influence of different ANG II concentrations (10(-7) et 10(-9) mol/L) on these rings as well as the effect of AT1 blockade by losartan (10(-7 mol/L). ANG II inhibited angiogenesis at 10(-7) mol/L on renal artery. However, these was a angiogenic effect at 10(-9) mol/L on the mesenteric artery. Every time losartan prevented the effect of ANG II in any kind of vessel rings. No significant effect on ANG II was found on aortic rings but coadministration of losartan induced a dramatic decrease in the number of capillary sprouts. In conclusion, ANG II seems to be deeply involved in angiogenesis. However, its effect depends on the concentration of ANG II and the type of vessel. ANG II appears to be angiogenic on mesenteric arteries via an AT1 receptor effect and mostly anti-angiogenic on the renal arteries with possible involvement of AT2 receptors.     

NADPH oxidase and enhanced superoxide generation in intrauterine undernourished rats: involvement of the renin-angiotensin system

OBJECTIVE: We previously reported that intrauterine undernutrition increased the oxidative stress by decreasing superoxide dismutase activity. In the present study, we tested whether NADPH oxidase, xanthine oxidase, cyclooxygenase or nitric oxide synthase are responsible for the increased O(2)(-) generation observed in rats submitted to intrauterine undernutrition. In addition, we investigated the effect of angiotensin II (ANG II) on O(2)(-) production via activation of NADPH oxidase. METHODS: Female pregnant Wistar rats were fed either normal or 50% of the normal intake diets, during the whole gestational period. At 16 weeks of age, the rats were used for the study of intravital fluorescence microscopy; microvascular reactivity, local ANG II concentration and AT(1), p22(phox) and gp91(phox) gene expression. In this study only the male offspring was used. RESULTS: Treatment of mesenteric arterioles with the xanthine oxidase inhibitor oxypurinol, the nitric oxide synthase inhibitor L-NAME or the cyclooxygenase inhibitor diclofenac did not significantly change superoxide production. Thus, these vascular sources of superoxide were not responsible for the increased superoxide concentration. In contrast, treatment with the NADPH oxidase inhibitor apocynin significantly decreased superoxide generation and improved vascular function. On the other hand, intrauterine undernutrition did not alter the gene expression for p22(phox) and gp91(phox). The fact that the local ANG II concentration was increased and the attenuation of oxidative stress by blocking AT(1) receptor with losartan, led us to suggest that ANG II induces O(2)(-) generation in intrauterine undernourished rats. CONCLUSION: Our study shows that NADPH oxidase inhibition attenuated superoxide anion generation and ameliorated vascular function in rats submitted to intrauterine undernutrition. Although it is not clear which mechanisms are responsible for the increase in NADPH oxidase activity, a role for ANG II-mediated superoxide production via activation of NADPH oxidase is suggested.     

Losartan and ozagrel reverse retinal arteriolar constriction in non-obese diabetic mice

Objective: Reductions in retinal blood flow are observed early in diabetes. Venules may influence arteriolar constriction and flow; therefore, we hypothesized that diabetes would induce the constriction of arterioles that are in close proximity to venules, with the constriction mediated by thromboxane and angiotensin II. Methods: Using nonobese diabetic (NOD) mice, retinal measurements were performed three weeks following the age at which glucose levels exceeded 200 mg/dL, with accompanying experiments on age‐matched normoglycemic NOD mice. The measurements included retinal arteriolar diameters and red blood cell velocities and were repeated following an injection of the thromboxane synthase inhibitor, ozagrel. Mice were subdivided into equal groups and given drinking water with or without the angiotensin II receptor antagonist, losartan. Results: Retinal arterioles were constricted in hyperglycemic mice, with a significant reduction in flow. However, not all arterioles were equally affected; the vasoconstriction was limited to arterioles that were in closer proximity to venules. The arteriolar vasoconstriction (mean arteriolar diameters = 51 ± 1 vs. 61 ± 1 μ m in controls; p < 0.01) was eliminated by both ozagrel (61 ± 2 μ m) and losartan (63 ± 2 μ m). Conclusions: Venule‐dependent arteriolar vasoconstriction in NOD mice is mediated by thromboxane and/or angiotensin II.     

Vascular neuroeffector function in two-kidney, one clip hypertensive dogs

In control dogs and those made hypertensive for 1 and 8 months by partially occluding a renal artery, contractile responses of mesenteric artery strips to adrenergic nerve stimulation and to norepinephrine, plasma renin activity and vascular angiotensin converting enzyme (ACE) activity were compared. Contractile responses to norepinephrine were potentiated in the artery strips from 8-month-hypertensive dogs; however, the response to electrical stimulation of adrenergic nerves was not influenced. Contractions induced by the nerve stimulation were potentiated by a low concentration (2 X 10(-10) mol/l) of angiotensin (ANG) II; the potentiating effect was enhanced in 8-month-hypertensive dog arteries. 3H-overflow evoked by adrenergic nerve stimulation was increased by ANG II to a greater extent in superfused mesenteric artery strips obtained from hypertensive (8-month) dogs, previously soaked in 3H-norepinephrine. Angiotensin converting enzyme activity was markedly greater in 8-month-hypertensive dog mesenteric arteries than in normotensive dog arteries. It may be concluded that the hypertension is maintained by increased sensitivity of post-synaptic alpha 1-adrenoceptors and pre-synaptic ANG receptors and increased vascular ACE activity, possibly promoting the production of ANG II in the vascular wall.     

Mesenteric vasoconstriction triggers nitric oxide overproduction in the superior mesenteric artery of portal hypertensive rats

BACKGROUND & AIMS: Vasoconstriction of the superior mesenteric artery (SMA) is the earliest hemodynamic event occurring after partial portal vein ligation (PVL). We tested the hypothesis that this early vasoconstriction of the SMA may initiate eNOS up-regulation in PVL. METHODS: Portal hypertension with or without mesenteric vasoconstriction was induced by differentially calibrated stenosis of the portal vein (PVL-20G and PVL-18G, respectively). In a separate group of rats, mesenteric vasoconstriction was achieved by renal artery ligation. Sham-operated rats were used as controls. Effects of vasoconstriction of the SMA in PVL and RAL rats were evaluated by measuring perfusion pressure changes in isolated SMA beds in response to methoxamine, nitric oxide synthase activity, and eNOS protein expression. Mean arterial pressure, portal pressure, and SMA blood flow were measured by catheterization and Doppler flowmetry. SMA vascular resistance was calculated from arterial pressure, portal pressure, and SMA flow. RESULTS: There was a significant increase in SMA vascular resistance in PVL-20G (2.33 +/- 0.13 vs. 1.22 +/- 0.03 mm Hg/% flow; P < 0.05) and RAL (2.32 +/- 0.18 vs. 1.18 +/- 0.02 mm Hg/% flow; P < 0.05) but not in PVL-18G, showing mesenteric vasoconstriction in both PVL-20G and RAL groups. The mesenteric vasculature of PVL-20G and RAL animals showed hyporeactivity to methoxamine (P < 0.01). Whereas both PVL groups were portal hypertensive (P < 0.01), RAL rats were not. The SMA hyporeactivity of PVL-20G and RAL rats was corrected by N(G)()-monomethyl-L-arginine, and nitric oxide synthase enzyme activity was significantly higher in PVL-20G and RAL rats (P < 0.05). CONCLUSIONS: Mesenteric arterial vasoconstriction plays a triggering role in up-regulation of eNOS catalytic activity in the SMA of portal hypertensive rats.     

Chronic angiotensin II infusion decreases renal norepinephrine overflow in conscious dogs

Sympathetic nerve activity and in particular renal sympathetic nerve activity were monitored in six conscious dogs subjected to 6 days of intravenous angiotensin (ANG II) infusion (20 ng/kg/min). This was accomplished by measurement of both arterial and renal venous plasma catecholamine concentration. During the initial 4 hours of ANG II infusion, mean arterial pressure (MAP) increased 35 +/- 8 mm Hg from a control value of 101 +/- 4 mm Hg. Although there were no significant changes in arterial plasma norepinephrine (NE) concentration at this time (control = 148 +/- 40 pg/ml), arterial plasma epinephrine (E) concentration increased threefold (control 42 +/- 15 pg/ml). After 24 hours of ANG II infusion, MAP remained elevated (132 +/- 5 mm Hg), but plasma E concentration returned to control levels. From Days 2 through 6 of ANG II infusion, MAP was elevated approximately 40 mm Hg, but there were no chronic increases in either arterial plasma E or NE concentrations. In contrast to arterial plasma catecholamine concentration, renal vein plasma NE concentration (control = 216 +/- 27 pg/ml) actually decreased during both the acute (122 +/- 12 pg/ml) and chronic (103 +/- 26 pg/ml) phases of ANG II infusion. Moreover, renal NE overflow (renal venous plasma NE concentration-arterial plasma NE concentration X effective renal plasma flow), an index of renal sympathetic nerve activity, was depressed during the chronic phase of ANG II hypertension. These results, therefore, do not support the contention that the sympathetic nervous system mediates the hypertension produced by elevated plasma levels of ANG II.(ABSTRACT TRUNCATED AT 250 WORDS)     

Neurohypophyseal and pituitary-adrenocortical responses to the alpha 1 agonist methoxamine in humans.

To test the hypothesis that the release of neurohypophyseal peptides into plasma in humans is stimulated by a central nervous system (CNS) alpha 1 adrenergic mechanism, we measured the responses of arginine vasopressin (AVP) and oxytocin (OT) to intravenous methoxamine, an alpha 1 agonist which enters the CNS following peripheral administration. The potential confound of baroreceptor inhibition of AVP release by the pressor effect of methoxamine was addressed by measuring the plasma AVP response to infusion of norepinephrine (NE), an alpha 1 agonist which does not enter the CNS and which produced an equivalent pressor effect. We also assessed the pituitary adrenocortical system responses to methoxamine and norepinephrine infusions by measuring plasma ACTH and cortisol concentrations. In addition, plasma NE and epinephrine were measured. Methoxamine, but not NE, increased plasma AVP compared to placebo infusion. Neither methoxamine nor NE affected plasma OT. The AVP elevation was delayed until more than 60 min after the methoxamine infusion began and the peak AVP level occurred 30 min after cessation of the infusion. In contrast, ACTH and cortisol increased early during methoxamine infusion and ACTH returned to baseline promptly after the infusion ceased. Although it is possible that the AVP response to methoxamine reflected stimulation of AVP release at a CNS level, it is also possible that the AVP increase represented a rebound response to withdrawal of methoxamine.     

Role of angiotensin II in regulation of basal and sympathetically stimulated vascular tone in early and advanced cirrhosis

BACKGROUND & AIMS: The renin-angiotensin and sympathetic nervous systems are activated in cirrhosis. This study aimed to establish the role of angiotensin II (ANG II) in the regulation of basal and sympathetically stimulated vascular tone in preascitic cirrhotic patients and patients with diuretic-refractory ascites compared with age- and sex-matched healthy controls. METHODS: Forearm blood flow (FBF) responses to lower body negative pressure (LBNP) and to subsystemic, intrabrachial infusions of losartan, an angiotensin II type 1 (AT(1)) receptor antagonist, norepinephrine, and ANG II were measured using venous occlusion plethysmography. RESULTS: In all groups, ANG II and norepinephrine caused dose-dependent reductions in FBF (P < 0.001); responses to norepinephrine were similar across the 3 groups but those to ANG II were less in both cirrhotic groups than in controls (P < 0.01). Losartan caused a dose-dependent increase in FBF only in patients with refractory ascites (P < 0.01). LBNP caused less reduction in FBF in refractory ascites patients than in both preascitic patients and controls (P < 0.01). CONCLUSIONS: Despite hyporesponsiveness to exogenous ANG II in both early and advanced cirrhosis, endogenous ANG II contributes to the maintenance of basal vascular tone only in advanced cirrhosis. These findings suggest a role of ANG II in the pathogenesis of ascites. Attenuated LBNP responses occurred only in advanced cirrhosis, without apparent interaction with endogenous ANG II.     

Inflammation-induced vasoconstrictor hyporeactivity is caused by oxidative stress

OBJECTIVES: We sought to determine the role of oxidative stress in the development of vascular dysfunction in inflammation. BACKGROUND: Hyporeactivity to catecholamines and other vasoconstrictors is present in acute inflammation. Because oxidative stress plays a significant role in inflammation, impaired responsiveness may be overcome by anti-oxidants. METHODS: In randomized, double-blind, cross-over studies, forearm blood flow (FBF) responses to norepinephrine (NE), angiotensin II (ANG II), and vasopressin (VP) were assessed before and 4 h after induction of systemic inflammation by low doses of Escherichia coli endotoxin (lipopolysaccharide [LPS], 20 IU/kg intravenously) or after placebo in healthy volunteers. Furthermore, the effect of intra-arterial vitamin C (24 mg/min) or placebo on NE-induced or ANG II-induced vasoconstriction was studied after LPS. RESULTS: Administration of LPS caused systemic and forearm vasodilation, increased white blood cell count, elevated body temperature, and reduced vitamin C plasma concentrations. Lipopolysaccharide decreased the responses of FBF to NE by 59%, to ANG II by 25%, and to VP by 51% (n = 9, p < 0.05, all effects). Co-administration of vitamin C completely restored the response to NE and to ANG II, which was comparable to that observed under baseline conditions (n = 8). CONCLUSIONS: E. coli-endotoxemia reduces FBF responsiveness to vasoconstrictors. The hyporeactivity can be corrected by high doses of vitamin C, suggesting that oxidative stress may represent an important target for inflammation-induced impaired vascular function.     

Possible modulation by endothelin-1, nitric oxide, prostaglandin I2 and thromboxane A2 of vasoconstriction induced by an α-agonist in mesenteric arterial bed from diabetic rats

Summary We hypothesized that in diabetes arterial reactivity to constrictors is attenuated by certain endothelium-derived substances. We examined the vasoconstriction induced by methoxamine (α₁-agonist) in isolated mesenteric arterial beds from streptozotocin (STZ)-induced diabetic rats and age-matched control rats. The dose-response curve for methoxamine was shifted to the right and the maximum contractile response was impaired in mesenteric arterial beds from diabetic rats. The methoxamine vasoconstriction was reduced in endothelium-denuded preparations from controls rats, but increased in those from diabetic rats. Treatment with the nitric oxide synthase inhibitor N^G-nitro-L-arginine enhanced the vasoconstrictions induced by methoxamine in both control and diabetic rats. Indomethacin had no effect on the methoxamine vasoconstriction in control rats, but it shifted the dose-response curve to the left in diabetic rats. Whether given with or without indomethacin, BQ-123, (an ET_A-receptor antagonist) plus BQ-788 (an ET_B-receptor antagonist) shifted the dose-response curve for methoxamine to the right in control rats (while reducing the maximum response) but to the left in diabetic rats. The methoxamine-stimulated release of 6-keto-prostaglandin F₁α from the mesenteric arterial bed in diabetic rats was approximately four times that seen in the control rats, while the methoxamine-induced release of thromboxane B₂ (TXB₂), a metabolite of thromboxane A₂ (TXA₂), was less in diabetic rats than in the control animals. These results suggest that an increased production of prostaglandin I₂ (PGI₂) and decreased formation of TXA₂ could be responsible for the attenuation of the methoxamine-induced mesenteric vasoconstriction seen in diabetic rats, and these changes in the diabetic state could be partly responsible for the lower blood pressure seen in our diabetic rats. [Diabetologia (1998) 41: 1410–1418] Received: 2 March 1998 and in final revised form: 10 August 1998     

Renal Uptake of Circulating Angiotensin II in Val5-Angiotensin II Infused Rats Is Mediated by AT1 Receptor

Previous studies have demonstrated that augmentation of intrarenal angiotensin II (ANG II) levels during ANG II induced hypertension involves both endogenous formation and accumulation of circulating ANG II. The present work extends these findings and determines whether accumulation of infused ANG II in the kidney requires AT₁ receptor activation by using Val⁵-ANG II as the infused peptide. Male Sprague-Dawley rats were uninephrectomized and divided into three groups: control (n = 6), Val⁵-ANG II (exogenous form) infused (n = 8), and Val⁵-ANG II infused rats treated with losartan (n = 8). Val⁵-ANG II, which has the same biological and immunoreactive properties as endogenous ANG II, was infused at 40 ng/min via an osmotic minipump implanted subcutaneously. By day 12, systolic blood pressure (SBP) increased significantly in Val⁵-ANG II infused rats (197 ± 7 mm Hg). As previously shown, the development of hypertension in ANG II infused rats was prevented by losartan treatment. Blood and kidney samples were harvested, subjected to HPLC to separate Val⁵-ANG II (exogenous) from Ile⁵-ANG II (endogenous) and the fractions were measured by radioimmunoassay. In the Val⁵-ANG II infused rats treated with losartan, total plasma ANG II levels were elevated to a greater extent than in rats not treated with losartan (289 ± 20 v 119 ± 14 fmol/mL). However, losartan markedly decreased by 88% the enhancement of intrarenal Val⁵-ANG II content that occurred in the rats infused with Val⁵-ANG II alone. These results demonstrate that AT₁ receptor blockade markedly reduces the intrarenal uptake of circulating ANG II that occurs in ANG II induced hypertension.     

Vasoconstrictor effect of aldosterone via angiotensin II type 1 (AT1) receptor: possible role of AT1 receptor dimerization

AIMS: We recently demonstrated that aldosterone induces a non-genomic vasoconstrictor effect on rat coronary arterioles and that this effect was blocked by angiotensin II type 1 receptor (AT1) blockers. Intracellular transglutaminase enhances AT1 signalling by cross-linking AT1 homodimers. The purpose of this study was to confirm the AT1-dependency of the vasoconstrictor effect of aldosterone using AT1a knockout (AT1aKO) mice and to investigate the role of intracellular transglutaminase and AT1 dimerization in this effect. METHODS AND RESULTS: The mesenteric arterioles (60-160 microm) were isolated from C57BL/6J (wild-type, WT) and AT1aKO mice, and the internal diameter was measured by video microscopy. Aldosterone (10(-13) to 10(-6) M), but not hydrocortisone, produced a dose-dependent vasoconstriction in WT mice; the maximal diameter change was -8.6 +/- 0.3% from the baseline (P < 0.001). This vasoconstrictor effect was unaffected by the mineralocorticoid receptor antagonist spironolactone or eplerenone, the AT2 antagonist PD123319, the glucocorticoid receptor antagonist RU486, or endothelium denudation. Aldosterone's vasoconstrictor effect was negligible in AT1aKO mice. The AT1 blockers valsartan or candesartan suppressed aldosterone-induced vasoconstriction in WT mice. The transglutaminase inhibitors cystamine and monodansyl cadaverine also suppressed the vasoconstrictor effect of aldosterone, without affecting the vasoconstrictor effect of angiotensin II in WT mice. AT1 dimer protein levels were increased in WT mesenteric arterioles treated with 10(-7) M aldosterone, and the transglutaminase inhibitor and AT1 blocker blocked this aldosterone-induced formation of AT1 dimer. Treatment with 10(-7) M aldosterone for 10 min increased the transglutaminase activity by 2.5 +/- 0.2-fold in cultured vascular smooth muscle cells and by 1.2 +/- 0.1-fold in the mesenteric arterioles. These increases were abolished by transglutaminase inhibitors. CONCLUSION: Aldosterone produces a non-genomic, endothelium-independent vasoconstrictor effect by enhancing intracellular transglutaminase activity and presumably inducing AT1 dimer formation in mesenteric arterioles.     

Contractile response of the isolated dorsal aorta of the snake to angiotensin II and norepinephrine

Vasopressor action is a phylogenetically old function of angiotensin (ANG) II. The action can be ascribed to both direct activation of vascular ANG II receptors and through catecholamine release. In the Rat snake, Ptyas korros, the possible presence of common adrenergic-ANG receptors and their involvement in this action have been proposed. In order to elucidate the vasopressor mechanism of ANG II in the snake, and to test the presence of common adrenergic-ANG receptors, the contractile response of isolated snake dorsal aorta to [Val5]ANG II and norepinephrine (NE) was studied using the cobra, Naja naja and the Rat snake, Ptyas korros. Both ANG II (3 X 10(-11) to 10(-6) M) and NE (10(-8) to 10(-5) M) produced a dose-dependent increase in tension in the aortic strips of Naja, which were more sensitive to ANG II. Phenotolamine, an alpha-adrenergic antagonist, competitively inhibited NE without altering the response to ANG II. [Sar1, Ala8]ANG II inhibited ANG II but did not affect the response to NE. A similar dose-dependent increase in tension in the aortic strips of Ptyas was seen with NE (10(-8) to 10(-5) M) but these strips did not respond to ANG II. These results suggest that functionally separate receptors for ANG II and NE exist in the dorsal aorta of the cobra and that local liberation of catecholamines from the adrenergic nerve terminals do not play a role in the expression of ANG II action. There also exist differences in the nature of ANG II action/receptors among different species of snakes and different vascular beds in the same species.     

Divergent roles of angiotensin II AT1 and AT2 receptors in modulating coronary microvascular function

Angiotensin II (Ang II) is a potent vasoconstrictor in the peripheral circulation and has been implicated in many cardiovascular diseases associated with elevated oxidative stress. However, its direct vasomotor action and its linkage to oxidative stress-induced vascular dysfunction in the coronary microcirculation remain elusive. In this study, we directly assessed the vasomotor action of Ang II in isolated porcine coronary arterioles and also examined whether Ang II can modulate endothelium-dependent nitric oxide (NO)-mediated dilation via superoxide production. Ang II evoked vasoconstriction at a low concentration (1 nmol/L) and dilations at higher concentrations (>10 nmol/L). Ang II type 1 (AT(1)) receptor antagonist losartan abolished vasoconstriction, whereas Ang II type 2 (AT(2)) receptor antagonist PD 123319 eliminated vasodilation. Adenosine stimulated a significant arteriolar NO production and dilation. NO synthase inhibitor N(G)-monomethyl-L-arginine (L-NMMA) abolished stimulated NO production and attenuated vasodilation. Pretreating vessels with a subvasomotor concentration of Ang II (0.1 nmol/L, 60 minutes) mimicked inhibitory effects of L-NMMA. Ang II-mediated inhibition was not observed in the presence of L-NMMA or after endothelial removal but was prevented by losartan, superoxide scavenger TEMPOL, or NADPH oxidase inhibitor apocynin. Dihydroethidium staining showed that Ang II elicited losartan- and TEMPOL-sensitive superoxide production in arterioles. These results demonstrate that Ang II evokes AT1 receptor-mediated vasoconstriction and AT2 receptor-mediated vasodilation of coronary arterioles. Ang II at a subvasomotor level impairs endothelium-dependent NO-mediated dilation attributable to elevated superoxide production via AT1 receptor activation of NADPH oxidase. These data may partly explain the impaired coronary flow regulation in heart diseases associated with an upregulated renin-angiotensin system.     

Structural changes vary along individual arterioles in deoxycorticosterone acetate hypertensive rats

The variability of structural changes along individual arterioles in deoxycorticosterone acetate (DOCA) hypertensive rats was measured by coefficients of variation of: (a) serial lumen diameters along microfil casts of individual mesenteric arterioles; and (b) wall and lumen indices in serial histological cross-sections along individual renal arterioles. The mean lumen diameter of third-order mesenteric arterioles decreased with increasing duration of hypertension. There was increased variability of lumen diameter along lengths of DOCA arterioles, the coefficient of variation at 10 weeks DOCA treatment being 20.2 +/- 0.6% compared to 9.2 +/- 0.2% in controls (P less than 0.001). Medial area to internal elastic lamina (IEL) radius ratio of renal arterioles was increased in DOCA rats compared with control rats (P less than 0.025) and its variability along individual arterioles expressed as the coefficient of variation was 31.70 +/- 3.87% in DOCA rats compared with 15.29 +/- 1.72% in controls (P less than 0.005). The observed increase in variability of lumen diameter and medial area along short lengths of individual arterioles in DOCA hypertensive rats indicates that hypertensive structural changes are probably not directly related to local blood pressure. We suggest that irregular functional vasoconstriction in hypertensive rats could account for this distribution of structural changes.     

Vascular angiotensin II receptor and calcium signaling in toadfish.

The renin-angiotensin system evolved during the early evolution of vertebrates and regulates blood pressure/blood volume homeostasis in nonmammalian and mammalian vertebrates. Properties of vascular angiotensin (ANG) receptors and signal pathways in primitive animals are, however, not well understood. We aimed to determine whether vascular ANG II receptors in the toadfish, Opsanus tau, an aglomerular teleost, pharmacologically resemble either the ANG subtype 1 receptor (AT1) or the subtype 2 receptor (AT2) by examining (i) the effects of selective ANG receptor antagonists on ANG II-induced vasopressor action and binding and (ii) ANG II's effect on cytosolic Ca2+ signaling. [Asn1, Val5]ANG II (native teleost ANG II) dose-dependently increased the mean arterial pressure of conscious toadfish. ANG II-induced pressor responses (100-500 ng/kg) were inhibited substantially (79-83%) by [Sar1, Ile8]ANG II (5 microg x kg-1 + 5 microg x kg-1 x min-1) and moderately (34-53%) by losartan (AT1 antagonist, 10 mg/kg + 20 mg x kg-1 x h-1) and by PD 123319 (AT2 antagonist, 10 mg/kg + 20 mg x kg-1 x h-1) (36-60%). Likewise, the [Asp1, Val5, His9]ANG I-induced pressor effect was completely eliminated by an ANG I-converting enzyme inhibitor, SQ 14,225. Specific 125I-ANG II binding to vascular smooth muscle (VSM) membrane fractions was displaced completely by [Asn1, Val5]ANG II and [Sar1, Ile8]ANG II. Losartan, but not PD 123319, partly displaced ANG II binding at 10(-10)-10(-6) M. Furthermore, ANG II (10(-7) or 10(-8) M) caused a rapid, transient increase in the cytosolic Ca2+ signal (fluorescence ratio (FR) of 340/380 nm) of isolated VSM tissues measured by fura-2 and a dual wavelength fluorospectrometer, whereas extracellular K+ induced sustained, dose-dependent (P < 0.01) increases in FR. The results indicate that toadfish VSM tissues possess a rather nonselective ANG receptor; partial inhibition of ANG II binding by losartan and stimulation of cytosolic Ca2+ signaling by ANG II suggest that the receptor has some resemblance to AT1 homologous receptors.