Altered coronary dilation in deoxycorticosterone acetate-salt hypertension

Additive damage in the thromboxane related vasoconstriction and bradykinin relaxation of intramural coronary resistance arterioles in a rodent model of andropausal hypertension

Hypertension and andropause both accelerate age–related vascular deterioration. We aimed to evaluate the effects of angiotensin-II induced hypertension and deficiency of testosterone combined regarding the resistance coronaries found intramurally.

Four male groups were formed from the animals: control group (Co, n = 10); the group that underwenr orchidectomy (ORC, n = 13), those that received an infusion of angiotensin-II (AII, n = 10) and a grous that received AII infusion and were also surgically orchidectomized (AII + ORC, n = 8). AII and AII + ORC animals were infused with infusing angiotensin-II (100 ng/min/kg) using osmotic minipumps. Orchidectomy was perfomed in the ORC and the AII + ORC groupsto establish deficiency regarding testosterone. Following four weeks of treatment, pressure-arteriography was performed in vitro, and the tone induced by administration of thromboxane-agonist (U46619) and bradykinin during analysis of the intramural coronaries (well-known to be resistance arterioles) was studied.

U46619-induced vasoconstriction poved to be significantly decreased in the ORC and AII + ORC groups when compared with Co and AII animals. In ORC and AII + ORC groups, the bradykinin-induced relaxation was also significantly reduced to a greater extent compared to Co and AII rats. Following orchidectomy, the vasocontraction and vasodilatation capacity of blood vessels is reduced. The effect of testosterone deficiency on constrictor tone and relaxation remains pronounced even in AII hypertension: testosterone deficiency further narrows adaptation range in the double noxa (AII + ORC) group. Our studies suggest that vascular changes caused by high blood pressure and testosterone deficiency together may significantly increase age-related cardiovascular risk.

Nitric oxide and coronary vascular endothelium adaptations in hypertension

This review highlights a number of nitric oxide (NO)-related mechanisms that contribute to coronary vascular function and that are likely affected by hypertension and thus become important clinically as potential considerations in prevention, diagnosis, and treatment of coronary complications of hypertension. Coronary vascular resistance is elevated in hypertension in part due to impaired endothelium-dependent function of coronary arteries. Several lines of evidence suggest that other NO synthase isoforms and dilators other than NO may compensate for impairments in endothelial NO synthase (eNOS) to protect coronary artery function, and that NO-dependent function of coronary blood vessels depends on the position of the vessel in the vascular tree. Adaptations in NOS isoforms in the coronary circulation to hypertension are not well described so the compensatory relationship between these and eNOS in hypertensive vessels is not clear. It is important to understand potential functional consequences of these adaptations as they will impact the efficacy of treatments designed to control hypertension and coronary vascular disease. Polymorphisms of the eNOS gene result in significant associations with incidence of hypertension, although mechanistic details linking the polymorphisms with alterations in coronary vasomotor responses and adaptations to hypertension are not established. This understanding should be developed in order to better predict those individuals at the highest risk for coronary vascular complications of hypertension. Greater endothelium-dependent dilation observed in female coronary arteries is likely related to endothelial Ca(2+) control and eNOS expression and activity. In hypertension models, the coronary vasculature has not been studied extensively to establish mechanisms for sex differences in NO-dependent function. Genomic and nongenomic effects of estrogen on eNOS and direct and indirect antioxidant activities of estrogen are discussed as potential mechanisms of interest in coronary circulation that could have implications for sex- and estrogen status-dependent therapy for hypertension and coronary dysfunction. The current review identifies some important basic knowledge gaps and speculates on the potential clinical relevance of hypertension adaptations in factors regulating coronary NO function.

Association of ornithine transcarbamylase gene polymorphisms with hypertension and coronary artery vasomotion

BACKGROUND

Previous studies have suggested that the activity of enzymes involved in the urea cycle may modulate nitric oxide (NO) production, arterial vasomotion, and hypertension. Our aim was to determine whether hypertension and coronary vasomotion could be associated with polymorphisms within the ornithine transcarbamylase (OTC) gene, located on chromosome X and coding for a key-enzyme of the urea cycle.

METHODS

Among 11 OTC polymorphisms that were originally selected from databases, the tag single-nucleotide polymorphism (SNP) rs5963409 and the independent SNP rs1800321 were tested for association with hypertension in two independent population samples recruited in Northern (Multinational MONItoring of trends and determinants in CArdiovascular disease (MONICA) study, n = 1,138) and Western (Etude du Vieillissement Artériel (EVA) study, n = 1,166) France. The vasomotor response of coronary arteries to methylergonovine maleate and isosorbide dinitrate was also evaluated in an independent sample (the vasomotion study, n = 121).

RESULTS

In males, the frequency of the rs5963409 minor allele was consistently higher in hypertensive (HT) than in normotensive subjects in the MONICA and EVA studies. In the combined sample, the rs5963409 minor allele was associated with an increased risk of hypertension (odds ratio (OR) (95% confidence interval (CI)) = 1.45 (1.10-1.90); P = 0.008). This association was independent of classical confounding factors. Consistently, rs5963409 minor allele was associated with a greater susceptibility to vasoconstriction in response to methylergonovine maleate (P = 0.0072). In contrast, no significant association between rs5963409 and hypertension could be detected in females.

CONCLUSION

Our results suggest that the OTC rs5963409 polymorphism may be associated with hypertension and coronary vasomotion in males.

Increased superoxide levels in ganglia and sympathoexcitation are involved in sarafotoxin 6c-induced hypertension

Endothelin (ET) type B receptors (ET(B)R) are expressed in multiple tissues and perform different functions depending on their location. ET(B)R mediate endothelium-dependent vasodilation, clearance of circulating ET, and diuretic effects; all of these should produce a fall in arterial blood pressure. However, we recently showed that chronic activation of ET(B)R in rats with the selective agonist sarafotoxin 6c (S6c) causes sustained hypertension. We have proposed that one mechanism of this effect is constriction of capacitance vessels. The current study was performed to determine whether S6c hypertension is caused by increased generation of reactive oxygen species (ROS) and/or activation of the sympathetic nervous system. The model used was continuous 5-day infusion of S6c into male Sprague-Dawley rats. No changes in superoxide anion levels in arteries and veins were found in hypertensive S6c-treated rats. However, superoxide levels were increased in sympathetic ganglia from S6c-treated rats. In addition, superoxide levels in ganglia increased progressively the longer the animals received S6c. Treatment with the antioxidant tempol impaired S6c-induced hypertension and decreased superoxide levels in ganglia. Acute ganglion blockade lowered blood pressure more in S6c-treated rats than in vehicle-treated rats. Although plasma norepinephrine levels were not increased in S6c hypertension, surgical ablation of the celiac ganglion plexus, which provides most of the sympathetic innervation to the splanchnic organs, significantly attenuated hypertension development. The results suggest that S6c-induced hypertension is partially mediated by sympathoexcitation to the splanchnic organs driven by increased oxidative stress in prevertebral sympathetic ganglia.

Effect of a methionine-supplemented diet on the blood pressure of Sprague–Dawley and deoxycorticosterone acetate–salt hypertensive rats

The objectives of the present study were to evaluate the effects of a methionine-supplemented diet on systolic blood pressure (BP) and vasomotor functions in Sprague–Dawley (SD) and deoxycorticosterone acetate (DOCA)–salt hypertensive rats. SD and DOCA rats were fed a normal or a methionine (8 g/kg)-supplemented diet for 10 weeks. Systolic BP was monitored and plasma homocysteine, methionine and cysteine levels were determined at the end of the experiment. Vasoconstriction and vasodilatation of aortic rings were measured. The methionine-supplemented diet induced a greater increase in homocysteinaemia concentration in DOCA rats than in SD rats and an increase in plasma cysteine concentration in DOCA rats. This diet was associated with an increase in systolic BP in SD rats and with a lesser development of DOCA–salt hypertension. An enhanced aortic constriction and a decreased responsiveness to acetylcholine, bradykinin and sodium nitroprusside in the SD rats fed the methionine-rich diet were consistent with the elevated systolic BP. In DOCA rats the increased responsiveness to bradykinin was in accordance with the systolic BP-lowering effect. In conclusion, the methionine-enriched diet cannot simply be considered as model of hyperhomocysteinaemia, since other metabolites and mechanisms seemed to be implicated in these complex interactions. The differential vasopressive effect of the methionine supplementation in SD and DOCA rats, and in particular the lowering of systolic BP obtained with a greater degree of hyperhomocysteinaemia in DOCA rats, suggest that more complex interactions exist between hyperhomocysteinaemia and BP than the simple positive association described previously.

Angiotensin-converting enzyme inhibitors reveal non-NO-, non-prostacycline-mediated endothelium-dependent relaxation in internal thoracic artery of hypertensive patients

BACKGROUND

We have shown that treatment of hypertension with ACE inhibitors (ACE-I) enhances relaxation to acetylcholine in human internal thoracic artery (ITA) above this in nonhypertensive patients receiving no ACE-I. Present study assesses the endothelium-dependent responses mediated by neither NO nor prostacyclin in human ITA.

METHODS

We compared isolated ITA rings from hypertensive patients treated with ACE-I (ACE-I group) with those from normotensive patients on no ACE-I (control group). Relaxation to acetylcholine was assessed before and after inhibition of NO synthase and cyclooxygenase with L-NMMA and indomethacin, respectively.

RESULTS

The maximal relaxation in ACE-I group was 79+/-3.3% and was depressed by incubation with L-NMMA and indomethacin to 41+/-2.7% (p<0.001); pD(2)=7.7+/-0.1 vs. 7.4+/-0.8 (p=0.265). The maximal relaxation to acetylcholine was lower in the control group: 65+/-3.3% (p=0.01); pD(2)=7.5+/-0.1 (p=0.07). Incubation with L-NMMA and indomethacin produced contraction to acetylcholine with a maximum of 43+/-7% (p<0.001); pD(2)=5.3+/-0.3 (p<0.001). The area under the concentration-response curve for acetylcholine-induced relaxation in ACE-I group equaled [arbitrary units] 596+/-71 and after incubation with L-NMMA and indomethacin 281+/-40 (p=0.002). Estimated LNMMA- and indomethacin-resistant relaxation, absent in control group, accounted for 47+/-4% of relaxation to acetylcholine in ACE-I group. Estimated NO- and prostacyclin-mediated relaxation was higher in control group than ACE-I group: 628+/-74 vs. 315+/-47 (p=0.009).

CONCLUSIONS

The results suggest that therapy with ACE-I improves endothelial function of hypertensive patients mainly by enhancing the endothelium-derived hyperpolarizing factor (EDHF) (and not NO)-mediated responses. It seems that it reveals measurable non-NO- non-PGI-mediated endothelium-dependent relaxation otherwise absent in conduit arteries.

NOS 3 subcellular localization in the regulation of nitric oxide production

Endothelium-derived nitric oxide (NO) is a key signalling molecule in the maintenance of cardiovascular health. Endothelial NO synthase (NOS 3), which catalyses the formation of NO, is targeted to the plasma membrane by dual acylation. In vitro studies suggest that membrane localization of NOS 3 is an important regulatory element of NO production. Dysfunction of the vascular endothelium and a decrease in NO bioavailability is associated with the development and progression of a number of cardiovascular diseases, including hypertension. Our laboratory has previously published that in salt-dependent hypertension there is an altered localization of NOS 3, with an increase in cytosolic expression. These data have led us to question whether the increased cytosolic NOS 3 expression is a form of compensation for endothelial dysfunction in hypertension, or an indicator and contributing factor to endothelial dysfunction. This review will outline the importance of subcellular localization in the regulation of NOS 3 in vitro, the role of NOS 3 in endothelial dysfunction associated with salt-dependent hypertension, and the potential physiological consequences of altered NOS 3 localization in vivo.

Tempol, an antioxidant, restores endothelium-derived hyperpolarizing factor-mediated vasodilation during hypertension

Acetylcholine releases a non-prostanoid endothelium-derived hyperpolarizing factor (EDHF) and nitric oxide from physiological salt solution perfused rat mesenteric arteries. This study reports an impairment in EDHF-mediated vasodilation in deoxycorticosterone acetate (DOCA)-salt hypertensive versus control normotensive rats. Nitric oxide-mediated vasodilation to acetylcholine was not altered in the animals. We hypothesize that free radical species generated as by-products of arachidonic acid metabolism contribute to impaired EDHF-mediated dilation in DOCA-salt hypertension. With or without reduced nicotinamide adenine dinucleotide phosphate (NADPH) as co-factor, arterial microsomes generate free radical species upon incubation with arachidonic acid. The production of free radicals was significantly higher in DOCA-salt versus control rat microsomes, and was totally eliminated by addition of cyclooxygenase-2 inhibitors NS-398 or celecoxib at 30 microM. Treatment of DOCA-salt rats with tempol (an antioxidant; 15 mg/kg, i.p., 21 days) alleviates hypertension; improves acetylcholine-induced EDHF-mediated vasodilation in DOCA-salt rats, and decreases arachidonic acid-driven microsomal free radical production. Serum level of 8-isoprostanes is elevated in DOCA-salt hypertension versus control or sham-salt rats, and the increase was reversed by tempol treatment. These results show that EDHF-mediated dilation of rat mesenteric arteries is impaired in DOCA-salt induced hypertension. Our data also suggest that cyclooxygenase-2 mediates free radical production, and that free radicals modulate the EDHF-mediated vascular response in DOCA-salt induced hypertension.

A study of the mediators involved in the protection induced by exogenous kinins in the isolated rat heart

The aim of this study was to determine whether endothelium-derived mediators and the endocannabinoid system were involved in the cardioprotective effects induced by exogenous kinins, namely bradykinin and its active metabolites, des-Arg(9)-bradykinin. Isolated rat hearts were submitted to a 20-min stabilisation period, followed by 90 min of low-flow ischemia (flow rate, 0.6 ml min(-1)) before a 60-min reperfusion period. Perfusion of bradykinin (BK, 30 nM) or des-Arg(9)-bradykinin (DBK, 30 nM) was initiated 1 min before the ischemia and maintained during the entire ischemic period. Perfusion with BK reduced infarct size, when measured at the end of the 60-min reperfusion. This effect was blocked by the B2-receptor antagonist, HOE140 (30 nM). Likewise, DBK reduced infarct size, effect that was blocked by the B1-receptor antagonist (30 nM Lys(0)-Leu(8)-DBK). The cardioprotective effect of both BK and DBK was abolished by the cannabinoid CB1-receptor antagonist (1 microM SR141716A), but not by the CB2-receptor antagonist (1 microM SR144528). Neither the NO synthase inhibitor, N-nitro-L-arginine (NNLA, 30 microM), the COX inhibitor, indomethacin (2.8 microM), nor the CYP450 inhibitor, clotrimazole (1 microM), prevented the cardioprotective effect of the kinins. However, a combined treatment with those three inhibitors abolished completely the ability of BK and DBK to reduce infarct size. In conclusion, exogenously administered BK and DBK exert a protective effect against ischemia in an isolated heart model. Endothelium-derived mediators such as nitric oxide, prostanoids, and endothelium-derived hyperpolarizing factor, as well as an SR141716A-sensitive mediator, appear to be involved in this beneficial effect.

Comparison of the cardiovascular protection by omapatrilat and lisinopril treatments in DOCA-salt hypertension

OBJECTIVE

To compare the cardiovascular protection provided by omapatrilat and lisinopril in an experimental model of hypertension.

METHODS

Four-week deoxycorticosterone acetate (DOCA)-salt hypertensive (HT) and age-matched normotensive (NT) rats were treated either with omapatrilat (40 mg/kg per day) or lisinopril (20 mg/kg per day) for 2 weeks before sacrifice, and compared with untreated HT and NT rats sacrificed at ages corresponding to either before or after the drug regimens.

RESULTS

Systolic arterial pressure (SAP) of 2 and 4 week HT rats was increased in comparison to age-matched NT rats (P <0.05). Treatment with omapatrilat or lisinopril reduced SAP in HT (P <0.05) similarly by about 10%. Cardiac interstitial collagen, perivascular collagen and media/lumen ratio of coronary arterioles were increased in HT rats. Both treatments partially prevented the rise in perivascular collagen and completely corrected the increased media/lumen ratio in small arterioles from HT (P <0.05). In contrast to NT rats, only a weak coronary dilatation to bradykinin was observed in Langendorff hearts isolated from untreated-HT. This response was slightly improved by lisinopril and markedly improved by omapatrilat (P <0.05). The coronary dilatation to SNP which was reduced in 4-week HT (P <0.05), was partially improved by omapatrilat treatment but not by lisinopril. The enhanced superoxide anion production in aorta from HT rats was partially corrected with omapatrilat and lisinopril. Finally, omapatrilat, unlike lisinopril, markedly reduced mortality in a more severe form of DOCA-salt hypertension.

CONCLUSIONS

Omapatrilat and lisinopril regressed coronary remodelling and cardiac collagen deposition, and reduced vascular oxidative stress in DOCA-salt hypertensive rats. However, despite similar antihypertensive efficacy, omapatrilat was superior to lisinopril in improving the endothelial-dependent coronary dilatation, suggesting a better vascular protection in the DOCA-salt model of hypertension.

Contribution of endogenous endothelin in the enhanced coronary constriction in DOCA-salt hypertensive rats

OBJECTIVE

The present study was performed to evaluate the hypersensitivity to vasoconstrictors in coronaries from uninephrectomized hypertensive rats (HTR), after a 2-week deoxycorticosterone acetate (DOCA)-salt treatment, in comparison with uninephrectomized age-matched normotensive rats (NTR).

DESIGN AND METHODS

Coronary resistance was recorded from isolated Langendorff hearts perfused at a constant flow rate.

RESULTS

Cumulative dose-response curves to vasopressin, angiotensin II and endothelin in HTR showed an enhanced maximal response, in comparison with NTR (P< 0.05). In contrast, the sensitivity to U-46619, a thromboxane-mimetic agonist, was reduced in HTR in comparison with NTR (P< 0.05). In the presence of ET(A)/ET(B)-receptor antagonists, LU-302 872 (10 micromol/l) and PD-142 893 (0.1-1 micromol/l), cumulative dose-response curves to vasopressin and angiotensin II showed a reduced maximal response in HTR compared with NTR (P< 0.05). LU-302 872 did not change the responsiveness to U-46619 in both groups. Perfusion of hearts from NTR with a subpressor concentration of endothelin-1 (10 pmol/l) potentiated the responsiveness to vasopressin and angiotensin II, but not that of U-46619 (P< 0.05). Hypertension did not alter the dose-response curves obtained with phorbol 12-myristate 13-acetate, an activator of protein kinase C, Bay K 8644, a L-type calcium-channel activator, and KCl. Measurement of endothelin release by radioimmunoassay in the coronary effluent, before and during dose-response curves to vasopressin, angiotensin II and U-46619, showed no significant increase by the vasoconstrictors, although basal endogenous endothelin was increased in HTR (P< 0.05).

CONCLUSION

Two-week DOCA-salt hypertension is associated with enhanced coronary vasoconstrictor effects of endothelin, vasopressin and angiotensin II. An increased basal release of endogenous endothelin in coronaries from HTR, along with an enhanced responsiveness of the coronary smooth muscle to endothelin, may contribute to the potentiated response to vasoconstrictors. L-type calcium-channels and protein kinase C are not involved in this increased coronary reactivity to vasoconstrictors in HTR.

Nitric oxide-independent effects of tempol on sympathetic nerve activity and blood pressure in DOCA-salt rats

The role of sympathetic nerves and nitric oxide (NO) in tempol-induced cardiovascular responses was evaluated in urethane-anesthetized sham and deoxycorticosterone acetate (DOCA)-salt-treated (DOCA-salt) rats. Tempol (30-300 micromol/kg iv), a superoxide (O) scavenger, decreased renal sympathetic nerve activity (RSNA), mean arterial pressure (MAP), and heart rate (HR) in DOCA-salt and sham rats. The antioxidants tiron and ascorbate did not alter MAP, HR, or RSNA in any rat. Tempol responses were unaffected after sham rats were treated with N(G)-nitro-L-arginine (L-NNA, 13 mg/kg). In DOCA-salt rats, L-NNA reduced tempol-induced depressor responses but not the inhibition of HR or RSNA. Tempol did not significantly decrease MAP, HR, or RSNA after hexamethonium (30 mg/kg iv) treatment in any rat. Dihydroethidine histochemistry revealed increased O levels in arteries and veins from DOCA-salt rats. Tempol treatment in vitro reduced O levels in arteries and veins from DOCA-salt rats. In conclusion, tempol-induced depressor responses are mediated largely by NO-independent sympathoinhibition in sham and DOCA-salt rats. There is an additional interaction between NO and tempol that contributes to depressor responses in DOCA-salt rats.