Occipital Artery Function during the Development of 2-Kidney, 1-Clip Hypertension in Rats.

This study compared the contractile responses elicited by angiotensin II (AII), arginine vasopressin (AVP), and 5-hydroxytryptamine (5-HT) in isolated occipital arteries (OAs) from sham-operated (SHAM) and 2-kidney, 1-clip (2K-1C) hypertensive rats. OAs were isolated and bisected into proximal segments (closer to the common carotid artery) and distal segments (closer to the nodose ganglion) and mounted separately on myographs. On day 9, 2K-1C rats had higher mean arterial blood pressures, heart rates, and plasma renin concentrations than SHAM rats. The contractile responses to AII were markedly diminished in both proximal and distal segments of OAs from 2K-1C rats as compared to those from SHAM rats. The responses elicited by AVP were substantially greater in distal than in proximal segments of OAs from SHAM rats and that AVP elicited similar responses in OA segments from 2K-1C rats. The responses elicited by 5-HT were similar in proximal and distal segments from SHAM and 2K-1C rats. These results demonstrate that continued exposure to circulating AII and AVP in 2K-1C rats reduces the contractile efficacy of AII but not AVP or 5-HT. The diminished responsiveness to AII may alter the physiological status of OAs in vivo.

Vasopressin-induced constriction of the isolated rat occipital artery is segment dependent.

BACKGROUND: Circulating factors delivered to the nodose ganglion (NG) by the occipital artery (OA) have been shown to affect vagal afferent activity, and thus the contractile state of the OA may influence blood flow to the NG. METHODS: OA were isolated and bisected into proximal and distal segments relative to the external carotid artery. RESULTS: Bisection highlighted stark differences between maximal contractile responses and OA sensitivity. Specifically, maximum responses to vasopressin and the V1 receptor agonist were significantly higher in distal than proximal segments. Distal segments were significantly more sensitive to 5-hydroxytryptamine (5-HT) and the 5-HT2 receptor agonist than proximal segments. Angiotensin II (AT)2, V2 and 5-HT(1B/1D) receptor agonists did not elicit vascular responses. Additionally, AT1 receptor agonists elicited mild, yet not significantly different maximal responses between segments. CONCLUSION: The results of this study are consistent with contractile properties of rat OA being mediated via AT1, V1 and 5-HT2 receptors and dependent upon the OA segment. Furthermore, vasopressin-induced constriction of the OA, regardless of a bolus dose or a first and second concentration-response curve, retained this unique segmental difference. We hypothesize that these segmental differences may be important in the regulation of blood flow through the OA in health and disease.

A novel vascular clip design for the reliable induction of 2-kidney, 1-clip hypertension in the rat.

The 2-kidney, 1-clip (2K1C) model has provided many insights into the pathogenesis of renovascular hypertension. However, studies using the 2K1C model often report low success rates of hypertension, with typical success rates of just 40-60%. We hypothesized that these low success rates are due to fundamental design flaws in the clips traditionally used in 2K1C models. Specifically, the gap widths of traditional silver clips may not be maintained during investigator handling and these clips may also be easily dislodged from the renal artery following placement. Therefore, we designed and tested a novel vascular clip possessing design features to maintain both gap width and position around the renal artery. In this initial study, application of these new clips to the left renal artery produced reliable and consistent levels of hypertension in rats. Nine-day application of clips with gap widths of 0.27, 0.25, and 0.23 mm elicited higher mean arterial blood pressures of 112 ± 4, 121 ± 6, and 135 ± 7 mmHg, respectively (n = 8 for each group), than those of sham-operated controls (95 ± 2 mmHg, n = 8). Moreover, 8 out of 8 rats in each of the 0.23 and 0.25 mm 2K1C groups were hypertensive, whereas 7 out of 8 rats in the 0.27 mm 2K1C group were hypertensive. Plasma renin concentrations were also increased in all 2K1C groups compared with sham-operated controls. In summary, this novel clip design may help eliminate the large degree of unreliability commonly encountered with the 2K1C model.

Evaluation of the possible role of prostaglandin F(2 alpha) in laminitis induced in horses by nasogastric administration of black walnut heartwood extract.

OBJECTIVE: To provide insights into the role of prostaglandin F(2 alpha) (PGF(2 alpha)) in the developmental stages of laminitis induced in horses by ingestion of black walnut heartwood extract (BWHE). SAMPLE POPULATION: 10 adult mixed-breed horses. PROCEDURES: Horses were separated into 2 groups and were euthanatized at 12 hours after placebo (water) administration (control horses) or after BWHE administration and development of Obel grade 1 laminitis. Blood samples were obtained to determine plasma PGF(2 alpha) concentrations hourly for the first 4 hours and subsequently every 2 hours after substance administration. Laminar arteries and veins were isolated, and responses to increasing concentrations of PGF(2 alpha) were measured before and after preincubation of blood vessels with prostanoid and thromboxane receptor antagonists SQ 29,548, SC-19220, and AH 6809. RESULTS: Plasma PGF(2 alpha) concentrations increased in horses given BWHE; the WBC count decreased concurrently. In control horses, PGF(2 alpha) was a potent contractile agonist for laminar veins but not for laminar arteries. In horses given BWHE, PGF(2 alpha) was similarly selective for laminar veins; however, the magnitude of PGF(2 alpha)-induced venoconstriction was less than that in control horses. After preincubation with SQ 29,548, laminar veins from control horses responded to PGF(2 alpha) with a small degree of dilation, whereas laminar veins from horses given BWHE did not. CONCLUSIONS AND CLINICAL RELEVANCE: PGF(2 alpha) may play a role in the inflammatory and vascular dysfunction associated with the prodromal stages of laminitis. Prostanoids such as PGF(2 alpha) may be viable targets for the prevention of acute laminitis in horses.

Thromboxane and isoprostanes as inflammatory and vasoactive mediators in black walnut heartwood extract induced equine laminitis.

Inflammation and vascular dysfunction occur concurrently during the prodromal stages of equine laminitis. The aim of this study was to provide insights into the role that thromboxane and isoprostanes may play in the development of black walnut heartwood extract (BWHE)-induced laminitis. Horses were divided into two groups, either control or BWHE-administered horses. Plasma concentrations of thromboxane increased transiently after administration of BWHE and coincided with the nadir in white blood cell counts, whereas plasma concentrations of iso-prostaglandin PGF(2alpha) (iso-PGF(2alpha)) did not change in either group. At 12h (for the control group) or Obel grade 1 laminitis (for the BWHE group) the horses were euthanized and laminar tissue collected. Laminar arteries and veins were used in functional studies with vasoconstrictor substances and tissue samples were used for the determination of laminar iso-PGF(2alpha) concentrations. Laminar tissue concentrations of iso-PGF(2alpha) were significantly greater in BWHE horses when compared to control horses. In parallel studies concentrations of iso-PGF(2alpha) in laminar tissue samples obtained 1.5 and 3h after administration of BWHE were indistinguishable from those for control horses at 3 or 12h after administration of an equal volume of water. Laminar vessel constrictor responses to either a thromboxane mimetic (U46619), iso-prostaglandin PGE(2) (iso-PGE(2)) or iso-PGF(2alpha) were determined using small vessel myographs. In some vessels, the effects of putative prostanoid and thromboxane receptor antagonists, SQ 29,548, SC-19220 and AH 6809, upon contractile responses were determined. In control horses, U46619, iso-PGF(2alpha) and iso-PGE(2) more potently and efficaciously constricted laminar veins when compared to laminar arteries. Responses of laminar veins from BWHE horses to iso-PGE(2) were similar to those of laminar veins from control horses, whereas iso-PGF(2alpha) elicited significantly greater responses in laminar veins from BWHE horses when compared to controls. In contrast, responses to U46619 were smaller in laminar veins isolated from BWHE horses when compared to those in laminar veins from control horses. In the presence of SQ 29,548, iso-PGF(2alpha) elicited a small dilation in laminar veins from control horses, which was not apparent in laminar veins from BWHE horses. These results are consistent with both systemic and local inflammatory events occurring during the prodromal stages of BWHE-induced laminitis. Because laminar veins are sensitive to thromboxane and isoprostanes, these substances may act as conduits between the inflammatory and vascular events occurring in laminitis and may be therapeutic targets for this crippling condition.

Equine laminitis: a journey to the dark side of venous.

Equine laminitis is a crippling condition that continues to defy repeated efforts to delineate the precise mechanisms involved and develop effective therapeutic strategies for use in the clinic. In this article, the possible role of dysfunction of the laminar vasculature is discussed, with particular emphasis on the venous side of the laminar microvasculature and the possible role(s) that metabolic syndrome and thrombosis may play in the dysfunction observed in the laminar microvasculature during the development of laminitis.

AMP-activated protein kinase and hypoxic pulmonary vasoconstriction.

Hypoxic pulmonary vasoconstriction is a vital homeostatic mechanism that aids ventilation-perfusion matching in the lung, for which the underlying mechanism(s) remains controversial. However, our most recent investigations strongly suggest that hypoxic pulmonary vasoconstriction is precipitated, at least in part, by the inhibition of mitochondrial oxidative phosphorylation by hypoxia, an increase in the AMP/ATP ratio and consequent activation of AMP-activated protein kinase (AMPK). Unfortunately, these studies lacked the definitive proof that can only be provided by selectively blocking AMPK-dependent signalling cascades. The aim of the present study was, therefore, to determine the effects of the AMPK inhibitor compound C upon: (1) phosphorylation in response to hypoxia of a classical AMPK substrate, acetyl CoA carboxylase, in rat pulmonary arterial smooth muscle and (2) hypoxic pulmonary vasoconstriction in rat isolated intrapulmonary arteries. Acetyl CoA carboxylase phosphorylation was increased approximately 3 fold in the presence of hypoxia (pO(2) = 16-21 mm Hg, 1 h) and 5-aminoimidazole-4-carboxamide riboside (AICAR; 1 mM; 4 h) and in a manner that was significantly attenuated by the AMPK antagonist compound C (40 microM). Most importantly, pre-incubation of intrapulmonary arteries with compound C (40 microM) inhibited phase II, but not phase I, of hypoxic pulmonary vasoconstriction. Likewise, compound C (40 microM) inhibited constriction by AICAR (1 mM). The results of the present study are consistent with the activation of AMPK being a key event in the initiation of the contractile response of pulmonary arteries to acute hypoxia.

Dietary structured lipids and phytosteryl esters: blood lipids and cardiovascular status in spontaneously hypertensive rats.

This study examined the dietary effects of enzymatically modified sesame oil with caprylic acid (structured lipids, SL) and phytosteryl esters (PE) on blood lipid profiles and cardiovascular parameters of spontaneously hypertensive rats (SHR) fed high-fat and high-cholesterol (HFHC) diets. The dietary groups were: normal diet (control), sesame oil (SO), SL, SO fortified with PE (SOP), and SL fortified with PE (SLP). After 9 weeks of feeding, the body weights, liver weights, and liver weight/body weight ratios in all HFHC-fed groups were higher than controls. Plasma total and LDL cholesterol levels in all HFHC-fed groups were similar to one another but higher than those in controls. Plasma HDL cholesterol levels in rats fed SOP and SLP were higher than those in controls or rats fed SO and SL. Plasma HDL/total cholesterol ratios in rats fed SOP and SLP were similar to those in controls and were higher than those in rats fed SO and SL. There was no difference in plasma lipid profiles between rats fed SO and SL. Arterial blood pressures (BP) in conscious HFHC-fed rats were similar to those in controls whereas heart rates (HR) in all HFHC-fed groups were similar to one another but were higher than that in controls. These findings demonstrate that (1) the dietary effects of SL on plasma lipid profiles and resting BP and HR are similar to those of SO, (2) PE had positive effects on plasma lipid profiles, and (3) 9-week intake of SL and PE did not have pronounced effects on resting BP but induced tachycardia in SHR.

Flavin adenine dinucleotide may release preformed stores of nitrosyl factors from the vascular endothelium of conscious rats.

This study determined whether flavin adenine dinucleotide (FAD) may elicit vasodilation in conscious rats via release of preformed endothelium-derived nitrosyl factors. Injections 1-6 (inj(1-6)) of FAD (2.5 micromol/kg, IV) elicited pronounced and equivalent vasodilator responses in saline-treated rats. Inj(1) of FAD elicited pronounced vasodilation in L-NAME-treated rats pretreated with the nitric oxide (NO) synthesis inhibitor, NG-nitro-L-arginine (L-NAME; 50 micromol/kg, IV), whereas Inj(2-6) elicited progressively smaller responses such that inj(6) elicited minor responses. The vasodilator responses elicited by the endothelium-dependent agonist, acetylcholine, were markedly attenuated in L-NAME-treated rats that had received inj(1-6) of FAD but not in saline-treated rats that had received inj(1-6) of FAD. The vasodilator actions of L-S-nitrosocysteine and the NO donor, sodium nitroprusside, were not diminished after the injections of FAD in saline- or in L-NAME-treated rats. Binding studies demonstrated that the densities of muscarinic M3 receptors were increased in thoracic aorta endothelium of rats treated with L-NAME + inj(1-6) of saline or L-NAME + inj(1-6) of FAD as compared to rats treated with saline + inj(1-6) of saline or saline + inj(1-6) of FAD. The progressive loss of response to injections of FAD in L-NAME-treated rats coupled with the loss of response to acetylcholine suggests that FAD elicits the use-dependent depletion of vesicular pools of nitrosyl factors in endothelial cells that cannot be replenished in the absence of NO synthesis.

Dietary effects of structured lipids and phytosteryl esters on cardiovascular function in spontaneously hypertensive rats.

This study examined the dietary effects of sesame oil (SO)-based structured lipids (SL) and phytosteryl esters (PE) on cardiovascular function in conscious spontaneously hypertensive rats (SHR) fed high-fat (HF) diets (20% w/w fat). The dietary groups were as follows: normal diet (4.5% w/w fat), SO, SO fortified with PE (SOP), SL, and SL fortified with PE (SLP). Mean arterial blood pressures were similar in all groups, whereas resting heart rates (HR) were higher in all HF-fed groups. The pressor responses to the alpha1-adrenoceptor agonist, phenylephrine (5 microg/kg), were similar in all groups. However, the pressor responses to phenylephrine (10 microg/kg) were diminished in SO- or SL-fed SHR, whereas they were not diminished in SOP- or SLP-fed SHR. The depressor responses elicited by the nitric oxide (NO) donor, sodium nitroprusside (5 and 10 microg/kg), were not diminished in HF-fed rats. Baroreflex-mediated changes in HR were variously decreased in the HF-fed groups, and this decrease tended to be greater in SOP and SLP than in SO and SL groups. The depressor and tachycardic responses elicited by the beta-adrenoceptor agonist, isoproterenol, were equivalent in all groups. The depressor responses elicited by the endothelium-dependent agonist, acetylcholine (0.1 microg/kg), and the hypertension elicited by the NO synthesis inhibitor, NG-nitro-L-arginine methylester (25 micromol/kg), were similar in all groups. These findings demonstrate that (1) HF diets increase resting HR and impair baroreflex function in SHR, whereas they do not obviously affect endothelium-dependent vasodilation, and (2) fortification with PE may be deleterious to cardiovascular function (eg, baroreflex activity) in SHR.

Effects of Rho-kinase and Src protein tyrosine kinase inhibition on agonist-induced vasoconstriction of arteries and veins of the equine laminar dermis.

OBJECTIVE: To determine the effects of inhibition of Rho-kinase or Src-family protein tyrosine kinases (srcPTK) on agonist-induced contractile responses in equine laminar arteries and veins. SAMPLE POPULATION: Laminar arteries and veins obtained from 13 adult mixed-breed horses. PROCEDURES: Laminar vessels were mounted on myographs and exposed to phenylephrine (PE), 5-hydroxytryptamine (5-HT), prostaglandin F(2) (PGF(2)), and endothelin-1 (ET-1) with or without the Rho-kinase inhibitor Y-27632 (10 microM), srcPTK inhibitor PP2 (10 microM), or a negative control analogue for PP2 (PP3; 10 microM). RESULTS: Responses to PE were reduced by use of Y-27632 in laminar vessels (approx inhibition, 55%). However, Y-27632 reduced responses to 5-HT to a greater degree in veins than in arteries (approx inhibition of 55% and 35%, respectively). The Y-27632 also reduced responses of laminar veins to ET-1 by approximately 40% but had no effect on maximum responses of laminar arteries to ET-1, although a rightward shift in the concentration response curve was evident. Addition of PP2 reduced responses to PE, 5-HT, and PGF(2) in laminar veins by approximately 40%, 60%, and 65%, respectively, compared with responses after the addition of PP3; PP2 had no effect on responses to ET-1. In laminar arteries, PP2 reduced 5-HT-induced contractions by approximately 50% but did not affect responses to PE or ET-1. CONCLUSIONS AND CLINICAL RELEVANCE: Results of the study were consistent with activation of Rho-kinase being important during agonist-induced constriction in laminar vessels, activation of srcPTK being an agonist-dependent event, and more prominent roles for Rhokinase and srcPTK in veins than in arteries.

Hemodynamic responses elicited by systemic injections of flavin adenine dinucleotide in anesthetized rats.

Flavin adenine dinucleotide (FAD) elicits an endothelium-dependent vasodilation in isolated rat mesenteric beds via activation of P2Y-purinoceptors. The aims of this study were to characterize the hemodynamic responses elicited by systemic injections of FAD and flavin mononucleotide (FMN) in anesthetized rats and to determine the role of nitric oxide synthase (NOS), cyclooxygenase, P2Y/P2X-purinoceptors, and muscarinic receptor in these responses. FAD (0.05-1.0 micromol/kg, iv) elicited dose-dependent decreases in heart rate (HR), mean arterial blood pressure (MAP), and hindquarter vascular resistance (HQR), whereas it elicited an initial increase and then a decrease in mesenteric (MR) vascular resistance. The FAD-induced responses were not affected by the P2Y/P2X-purinoceptor antagonist suramin, the muscarinic receptor antagonist methyl-atropine, or the cyclooxygenase inhibitor indomethacin. The vasodilator actions of FAD were unaffected by the NOS inhibitor N-nitro-L-arginine methyl ester (L-NAME), whereas the bradycardia elicited by higher doses of FAD were diminished by L-NAME. FMN did not elicit hemodynamic responses in the absence or presence of L-NAME. In summary, FAD-induced bradycardia depends, in part, on the activation of NOS, whereas the vasodilator actions of FAD are not obviously due to newly synthesized nitrosyl factors. These findings and those in our companion manuscript support the concepts that the adenine moiety confers biological activity to FAD, which releases preformed pools of nitrosyl factors.

Effect of voltage-gated and capacitative calcium entry blockade on agonist-induced constriction of equine laminar blood vessels.

OBJECTIVE: To characterize the relative contributions of voltage-gated and capacitative Ca(2+) entry to agonist-induced contractions of equine laminar arteries and veins. ANIMALS: 16 adult mixed-breed horses. PROCEDURES: Laminar arteries and veins were isolated and mounted on small vessel myographs for the measurement of isometric tension. Concentration-response curves were obtained for the vasoconstrictor agonists phenylephrine, 5-hydroxytryptamine (5-HT), prostaglandin F(2) (PGF(2)), and endothelin-1 (ET-1) either in the absence of extracellular Ca(2+) or in the presence of the voltage-gated Ca(2+) channel inhibitor diltiazem or the putative inhibitor of capacitative Ca(2+) entry, trifluoromethylphenylimidazole. RESULTS: In the absence of extracellular Ca(2+), maximal responses of veins to 5-HT, phenylephrine, ET-1 and PGF(2) were reduced by 80%, 50%, 50%, and 45%, respectively; responses of arteries to 5-HT, phenylephrine, and ET-1 were reduced by 95%, 90%, and 20%, respectively. Although diltiazem did not affect the maximal responses of veins to any agonist, responses of arteries to 5-HT, phenylephrine, and ET-1 were reduced by 40%, 50%, and 27%, respectively. Trifluoromethylphenylimidazole did not affect maximal responses of veins, but did reduce their contractile responses to low concentrations of ET-1 and PGF(2). CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that the contribution of extracellular Ca(2+) to laminar vessel contractile responses differs between arteries and veins and also between contractile agonists, voltage-gated Ca(2+) entry is more predominant in laminar arteries than in veins, and capacitative Ca(2+) entry has a minor role in agonist-induced contractile responses of laminar veins.

Evaluation of activation of protein kinase C during agonist-induced constriction of veins isolated from the laminar dermis of horses.

OBJECTIVE: To determine the effects of the protein kinase C (PKC) inhibitor, Ro-31-8220, on agonist-induced constriction of laminar arteries and veins obtained from horses. SAMPLE POPULATION: Laminar arteries and veins obtained from 8 adult mixed-breed horses. PROCEDURES: Laminar arteries and veins were isolated and mounted on small vessel myographs for the measurement of isometric tension. Concentration-response curves were then obtained for the vasoconstrictor agonists phenylephrine, 5-hydroxytryptamine, prostaglandin F(2), and endothelin-1. All responses were measured with or without the addition of Ro-31-8220 (3 microM). RESULTS: Laminar veins were more sensitive to vasoconstrictor agonists than laminar arteries, and incubation of laminar veins with Ro-31-8220 resulted in significantly smaller agonist-induced contractile responses for all agonists tested. In contrast, Ro-31-8220 had no effect on agonist-induced contractile responses of laminar arteries. CONCLUSIONS AND CLINICAL RELEVANCE: Results of the study were consistent with activation of PKC being confined to agonist-induced contraction of laminar veins isolated from the laminar dermis of horses. Consequently, the possible involvement of PKC in the venoconstriction observed during the development of laminitis is worthy of further investigation.

Differential effects of peroxynitrite on the function of arginine vasopressin V(1a) receptors and alpha(1)-adrenoceptors in vivo.

OBJECTIVE: The aim of this study was to provide evidence that peroxynitrite may differentially affect the function of arginine vasopressin (AVP) V(1a) receptors and alpha(1)-adrenoceptors in vascular smooth muscle of the rat METHODS: The vasoconstrictor responses elicited by AVP, or the alpha(1)-adrenoceptor agonist, phenylephrine, were determined in anesthetized rats before and after injections of (i) peroxynitrite, the thiol chelator, para-hydroxymercurobenzoic acid (PHMBA), or the electron acceptor, nitroblue tetrazolium (NBT). The ability of the reducing agent, glutathione, to reverse the loss of response to phenylephrine and AVP in peroxynitrite-treated rats was also examined. RESULTS: The AVP-induced responses were suppressed 10-20 min but not 60-70 min after the administration of peroxynitrite. Glutathione reversed the above loss of response to AVP at 10-20 min. The responses elicited by phenylephrine were suppressed 10-20 min and 60-70 min after administration of peroxynitrite. Glutathione did not reverse the above losses of response to phenylephrine. In addition, the vasoconstrictor actions of AVP and phenylephrine were markedly suppressed after administration of PHMBA or nitroblue tetrazolium. CONCLUSIONS: The above findings provide evidence that exogenously administered peroxynitrite may differentially affect the function of AVP V(1a) receptors and alpha(1)-adrenoceptors in vascular smooth muscle of the rat. The possibility that peroxynitrite impairs AVP V(1a) receptor function by transient oxidation events whereas peroxynitrite impairs alpha(1)-adrenoceptor function by transient oxidation and permanent nitration events will be discussed.

Differential effects of ouabain on the vasodilator actions of nitric oxide and S-nitrosothiols in vivo: relevance to the identity of EDRF/EDHF.

OBJECTIVES: This study examined the role of Na+/K+-ATPase in the vasodilator actions of nitric oxide (NO), S-nitrosothiols and the endothelium-dependent agonist, acetylcholine. METHODS: The vasodilator responses elicited by intravenous injections of (i) the NO-donors, sodium nitroprusside and MAHMA NONOate, (ii) the S-nitrosothiols, L-S-nitrosocysteine and S-nitrosocoenzyme A, and (iii) acetylcholine, in urethane-anesthetized rats. RESULTS: The NO-donors, S-nitrosothiols and acetylcholine elicited dose-dependent depressor responses and reductions in hindquarter (HQR) and mesenteric (MR) vascular resistances. The depressor responses and associated reductions in HQR elicited by NO-donors were markedly attenuated after injection of ouabain. In contrast, the depressor responses and reductions in HQR elicited by the S-nitrosothiols and acetylcholine were not affected. The reductions in MR elicited by all vasodilator agents were exaggerated after injection of ouabain. Finally, the decomposition of sodium nitroprusside, MAHMA NONOate, L-S-nitrosocysteine and S-nitrosocoenzyme A to NO upon addition to rat blood or vascular preparations was not affected by ouabain. CONCLUSION: This study demonstrates that ouabain has opposing effects on NO-mediated vasodilation in resistance arteries in the hindquarter and mesenteric beds of the rat. The similarity of effects of ouabain on the vasodilator actions of acetylcholine, L-S-nitrosocysteine and S-nitrosocoenzyme A as opposed to the NO-donors supports the possibility that endothelium-derived relaxing factor released by acetylcholine in resistance arteries is an S-nitrosothiol.

ACE inhibition restores the vasodilator potency of the endothelium-derived relaxing factor, L-S-nitrosocysteine, in conscious Spontaneously Hypertensive rats.

OBJECTIVE: The major aim of this study was to determine whether the angiotensin converting enzyme (ACE) inhibitors, captopril or enalapril, restore the diminished vasodilator potency of the endothelium-dependent agonist, acetylcholine (ACh), and the endothelium-derived relaxing factor (EDRF), L-S-nitrosocysteine (L-SNC), in conscious Spontaneously Hypertensive (SH) rats. METHODS: The hemodynamic responses elicited by i.v. injections of ACh, L-SNC, and nitric oxide donors such as MAHMA NONOate, were determined in SH rats treated for 7 days with captopril, enalapril, or the direct vasodilator hydralazine. The effects of captopril, enalapril or hydralazine on oxidant stress levels in blood serum and aorta of WKY and SH rats were also determined. RESULTS: Captopril, enalapril and hydralazine elicited equivalent falls in mean arterial pressure and systemic vascular resistances in SH rats. ACh- and L-SNC-induced vasodilation were increased in captopril- or enalapril-treated SH rats such that the responses were equal to those in normotensive Wistar Kyoto rats. The attenuated responses of ACh and L-SNC in SH rats were not improved by hydralazine. The vasodilator effects of MAHMA NONOate, which were substantially augmented in SH rats, were not affected by captopril, enalapril or hydralazine. The levels of oxidant stress were markedly reduced in captopril- or enalapril-treated but not hydralazine-treated SH rats. CONCLUSIONS: The finding that the ACE inhibitors improved the vasodilator potencies of L-SNC and the EDRF released by ACh in SH rats, suggests that the diminished vasodilator potency of these compounds was due to augmented ACE activity, which increased oxidant stress levels. This study provides the first evidence to support the concept that ACE inhibition lowers arterial pressure in SH rats, at least in part, by restoring the vasodilator potency of endothelium-derived L-SNC.

The vasodilator potency of the endothelium-derived relaxing factor, L-S-nitrosocysteine, is impaired in conscious spontaneously hypertensive rats.

OBJECTIVE: This study compared the hemodynamic responses elicited by the endothelium-derived relaxing factor (EDRF), L-S-nitrosocysteine (L-SNC), the non-prostanoid EDRF released by acetylcholine (ACh) and nitric oxide (NO)-donors such as MAHMA NONOate, in conscious spontaneously hypertensive (SH) and normotensive Wistar-Kyoto (WKY) rats. METHODS: The depressor and/or vasodilator responses elicited by intravenous injections of ACh, L-SNC and MAHMA NONOate were determined in adult WKY and SH rats before and after intravenous injection of the NO synthesis inhibitor, N(G)-nitro-L-arginine methylester (L-NAME), or the cyclooxygenase inhibitor, indomethacin. RESULTS: The responses elicited by ACh and L-SNC were smaller in SH than in WKY rats whereas the responses elicited by MAHMA NONOate were augmented in SH rats. The ACh-induced responses were not diminished after injection of L-NAME in WKY or SH rats. Indomethacin did not affect the responses to any of the vasodilator agents in WKY or SH rats. Addition of L-SNC to whole blood or thoracic aortae from SH rats yielded similar amounts of NO to those of WKY rats. CONCLUSIONS: The vasodilator potencies of ACh and L-SNC were diminished whereas that of NO was augmented in SH rats. The loss of potency of L-SNC in SH rats was not obviously due to differences in decomposition to NO or the overactivity of cyclooxygenase factors. This study provides the first evidence that diminished endothelium-dependent vasodilation in SH rats may involve a loss of vasodilator potency of endogenous L-SNC.