Endothelin in the splanchnic vascular bed of DOCA-salt hypertensive rats

Vascular capacitance is reduced by endothelin-1 (ET-1) in deoxycorticosterone (DOCA)-salt hypertensive rats. This may contribute to hypertension development. Because the splanchnic blood vessels (especially veins) are important in determining vascular capacitance, we tested the hypothesis that ET-1 levels in the splanchnic vasculature are elevated in hypertensive DOCA-salt compared with normotensive rats. Tissue ET-1 content was measured by ELISA in aorta, vena cava, superior mesenteric artery and vein, and small mesenteric arteries and veins from normotensive sham-operated (sham) and 4-wk DOCA-salt rats. We also determined ET-1 concentration in aortic and portal venous blood (draining the nonhepatic splanchnic organs) in anesthetized and conscious sham and DOCA-salt rats before and after acute blockade of ETB receptor-mediated plasma clearance of ET-1. Results showed a higher ET-1 content in veins than in arteries of similar size. However, ET-1 content was similar in vessels from sham and DOCA-salt rats, except in aorta and superior mesenteric artery, where ET-1 content was greater in DOCA-salt rats. ET-1 concentration was significantly higher in portal venous than in aortic blood, indicating net nonhepatic splanchnic release (nNHSR) of ET-1. However, nNHSR of ET-1 was similar in sham and DOCA-salt rats. Although nNHSR of ET-1 increased significantly after ETB receptor blockade in sham rats, it was completely unchanged in DOCA-salt rats. These data suggest that, despite the absence of ETB receptor-mediated plasma clearance of ET-1, neither the venous peptide content nor the net release of ET-1 is increased in the splanchnic vasculature of DOCA-salt rats. These results argue against the hypothesis that increased venomotor tone in DOCA-salt hypertension is caused by increased ET-1 concentration around splanchnic venous smooth muscle cells.     

Splanchnic sympathetic nerves in the development of mild DOCA-salt hypertension

We previously reported that mild deoxycorticosterone acetate (DOCA)-salt hypertension develops in the absence of generalized sympathoexcitation. However, sympathetic nervous system activity (SNA) is regionally heterogeneous, so we began to investigate the role of sympathetic nerves to specific regions. Our first study on that possibility revealed no contribution of renal nerves to hypertension development. The splanchnic sympathetic nerves are implicated in blood pressure (BP) regulation because splanchnic denervation effectively lowers BP in human hypertension. Here we tested the hypothesis that splanchnic SNA contributes to the development of mild DOCA-salt hypertension. Splanchnic denervation was achieved by celiac ganglionectomy (CGX) in one group of rats while another group underwent sham surgery (SHAM-GX). After DOCA treatment (50 mg/kg) in rats with both kidneys intact, CGX rats exhibited a significantly attenuated increase in BP compared with SHAM-GX rats (15.6 ± 2.2 vs. 25.6 ± 2.2 mmHg, day 28 after DOCA treatment). In other rats, whole body norepinephrine (NE) spillover, measured to determine if CGX attenuated hypertension development by reducing global SNA, was not found to be different between SHAM-GX and CGX rats. In a third group, nonhepatic splanchnic NE spillover was measured as an index of splanchnic SNA, but this was not different between SHAM (non-DOCA-treated) and DOCA rats during hypertension development. In a final group, CGX effectively abolished nonhepatic splanchnic NE spillover. These data suggest that an intact splanchnic innervation is necessary for mild DOCA-salt hypertension development but not increased splanchnic SNA or NE release. Increased splanchnic vascular reactivity to NE during DOCA-salt treatment is one possible explanation.     

Increased substance P content in nerve fibers associated with mesenteric veins from deoxycorticosterone acetate (DOCA)-salt hypertensive rats

This study examined sensory nerves associated with mesenteric arteries and veins in sham and deoxycorticosterone acetate (DOCA)-salt hypertensive rats. Reactivity of arteries and veins to substances released from sensory nerves was also studied in vitro using computer-assisted video microscopy. Co-localization of substance P (SP) and calcitonin gene-related peptide (CGRP) immunoreactivity (ir) was used to evaluate perivascular sensory nerves. Radioimmunoassay was used to quantify SP- and CGRP-ir content. Immunohistochemical studies revealed a plexus of SP/CGRP-ir nerves associated with arteries and veins. The intensity of SP-ir, but not CGRP-ir labeling was greater in arteries and veins from DOCA-salt compared to sham rats. RIA measurements revealed that the CGRP-ir content of arteries and veins was higher than the SP-ir content but there was a significant increase in SP-ir, but not CGRP-ir, content in arteries and veins from DOCA-salt rats. SP (0.03-1 microM) contracted veins and the NK-3 receptor agonist, senktide, mimicked this effect. There were no differences in SP or senktide reactivity of veins from sham or DOCA-salt rats. SP, but not senktide, relaxed KCl (40 mM) preconstricted arteries. CGRP (0.3 microM), acetylcholine (10 microM) and capsaicin (1 microM) relaxed KCl-preconstricted arteries and veins. The NK-1 receptor agonist, substance P methyl ester relaxed arteries but not veins. These data indicate that DOCA-salt hypertension is associated with upregulation of SP content in perivascular nerves. NK-3 receptors mediate venoconstriction which is unchanged in DOCA-salt hypertension. Increased release of SP from perivenous nerves might contribute to the increased venomotor tone in DOCA-salt hypertension.     

Impaired function of alpha2-adrenergic autoreceptors on sympathetic nerves associated with mesenteric arteries and veins in DOCA-salt hypertension

The present study tested the hypothesis that there is impaired function of alpha(2)-adrenergic autoreceptors and increased transmitter release from sympathetic nerves associated with mesenteric arteries and veins from DOCA-salt rats. High-performance liquid chromatography was used to measure the overflow of ATP and norepinephrine (NE) from electrically stimulated mesenteric artery and vein preparations in vitro. In sham arteries, nerve stimulation evoked a 1.5-fold increase in NE release, whereas in DOCA-salt arteries there was a 3.9-fold increase in NE release over basal levels (P < 0.05). In contrast, stimulated ATP release was not different in DOCA-salt arteries compared with sham arteries. In sham veins, nerve stimulation evoked a 2.9-fold increase in NE release, whereas in DOCA-salt veins there was a 8.4-fold increase in NE release over basal levels (P < 0.05). In sham rats NE release, normalized to basal levels, was greater in veins than in arteries (P < 0.05). The alpha(2)-adrenergic receptor antagonist yohimbine (1 microM) increased ATP and NE release in sham but not DOCA-salt arteries. The alpha(2)-adrenergic receptor agonist UK-14304 (10 microM) decreased ATP release in sham but not DOCA-salt arteries. In sham veins, UK-14304 decreased, but yohimbine increased, NE release; effects that were not observed in DOCA-salt veins. These data show that nerve stimulation causes a greater increase in NE release from nerves associated with veins compared with arteries. In addition, impairment of alpha(2)-adrenergic autoreceptor function in sympathetic nerves associated with arteries and veins from DOCA-salt rats results in increased NE release.     

Role of ET-1 receptor binding and [Ca(2+)](i) in contraction of coronary arteries from DOCA-salt hypertensive rats

Hypertension is associated with an increase in coronary artery disease, but little is known about the regulation of coronary vascular tone by endothelin-1 (ET-1) in hypertension. The present study evaluated the mechanisms mediating altered contraction to ET-1 in coronary small arteries from deoxycorticosterone acetate (DOCA)-salt hypertensive rats. DOCA-salt rats exhibited an increase in systolic blood pressure and plasma ET-1 levels compared with placebo rats. Contraction to ET-1 (1 x 10(-11) to 3 x 10(-8) M), measured in isolated coronary small arteries maintained at a constant intraluminal pressure of 40 mmHg, was largely reduced in vessels from DOCA-salt rats compared with placebo rats. To determine the role of endothelin receptor binding in the impaired contraction to ET-1, (125)I-labeled ET-1 receptor binding was measured in membranes isolated from coronary small arteries. Maximum binding (fmol/mg protein) and binding affinity were similar in coronary membranes from DOCA-salt rats compared with placebo rats. Changes in intracellular Ca(2+) concentration ([Ca(2+)](i)) were measured in freshly dissociated coronary small artery smooth muscle cells loaded with fura 2. ET-1 (10(-9) M) produced a 30 +/- 9% increase in [Ca(2+)](i) in smooth muscle cells from placebo rats, but had no effect on cells from DOCA-salt rats (2 +/- 2%). In summary, the ET-1-induced coronary artery contraction and increase in [Ca(2+)](i) are impaired in DOCA-salt hypertensive rats, whereas endothelin receptor binding is not altered. These results suggest endothelin receptor uncoupling from signaling mechanisms and indicate that impaired [Ca(2+)](i) signaling contributes to the decrease in ET-1-induced contraction of coronary small arteries in DOCA-salt hypertensive rats.     

Endothelin-3-dependent pulmonary vasoconstriction in monocrotaline-induced pulmonary arterial hypertension

Blockade of the endothelin (ET) system is beneficial in pulmonary arterial hypertension (PAH). The contribution of ET-3 and its interactions with ET receptors have never been evaluated in the monocrotaline (MCT)-induced model of PAH. Vasoreactivity of pulmonary arteries was investigated; ET-3 localization was determined by confocal imaging and gene expression of prepro-ET-3 quantified using RT-PCR. ET-3 plasma levels tended to increase in PAH. ET-3 localized in the media of pulmonary arteries, where gene expression of prepro-ET-3 was reduced in PAH. ET-3 induced similar pulmonary vasoconstrictions in sham and PAH rats. In sham rats, the ET(A) antagonist A-147627 (10nmol/l) significantly reduced the maximal response to ET-3 (E(max) 77+/-1 to 46+/-2%, mean+/-S.E.M., P<0.001), while the ET(B) antagonist A-192621 (1mumol/l) reduced the sensitivity (EC(50) 21+/-7 to 59+/-16nmol/l, P<0.05) without affecting E(max). The combination of both antagonists completely abolished ET-3-induced pulmonary vasoconstriction. In PAH, the ET(A) antagonist further reduced the maximal response to ET-3 and shifted the EC(50) (E(max) 23+/-2%, P<0.001, EC(50) 104+/-24nmol/l, P<0.05), while the ET(B) antagonist only shifted the EC(50) (123+/-36nmol/l, P<0.05) without affecting the E(max). In PAH, dual ET receptor inhibition did not further reduce constriction compared to selective ET(A) inhibition. ET-3 significantly contributes to pulmonary vasoconstriction by activating the ET(B) at low concentration, and the ET(A) at high concentration. The increased inhibitory effect of the ET(A) antagonist in PAH suggests that the contribution of ET(B) to ET-3-induced vasoconstriction is reduced. Although ET-3 is a potent pulmonary vasoconstrictor in PAH, its potential pathophysiologic contribution remains uncertain.     

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.     

Effects of acute and chronic administration of sotalol on the blood pressure and the sympathoadrenal activity of anesthetized deoxycorticosterone acetate-salt hypertensive rats

Using plasma catecholamine (CA) levels as an index of the sympathoadrenal activity, the effects of chronic and acute beta-blockade on the blood pressure and sympathetic activity were evaluated in deoxycorticosterone acetate (DOCA) - salt hypertensive (HT) rats. The acute administration of one beta-blocker (sotalol, 5 mg/kg) to intact of vagotomized anesthetized HT animals induced a significant decrease in plasma norepinephrine (NE) concentrations and mean arterial pressure (MAP). The amplitude of the decrease of the MAP or NE levels were linearly correlated with the basal NE levels, suggesting that sotalol reduced the blood pressure and sympathetic NE release more efficiently in rats with increased sympathetic activity. Similarly, chronic infusion of sotalol (1.5 mg X day-1 X rat-1) through an osmotic pump for 12 days in DOCA-salt HT rats significantly reduced NE and epinephrine (E) plasma levels compared with those observed in untreated DOCA-salt HT rats. Moreover, the chronic treatment with sotalol significantly reduced the plasma E elevation induced by bilateral carotid occlusion (CO) in vagotomized normotensive (NT) and HT rats. It therefore appears that acute administration of sotalol to HT rats causes a significant reduction in the sympathetic activity which is associated to a decrease in MAP. Although chronic sotalol treatment causes a significant reduction in the sympathoadrenal basal activity and in the adrenal reactivity, this treatment did not prevent the development of DOCA-salt hypertension.     

Plasma concentrations of endothelin-1 in spontaneously hypertensive rats and DOCA-salt hypertensive rats

To investigate the possible involvement of endothelin-1 (ET-1), an endothelium-derived potent vasoconstrictor peptide, in the pathophysiology of hypertension, plasma ET-1 levels in 15-week-old spontaneously hypertensive rats (SHR) and DOCA-salt hypertensive rats were measured with a sandwich-type enzyme immunoassay. The vasocontractile effect of ET-1 in aortic helical preparations was significantly more sensitive in DOCA-salt hypertensive rats than in control sham-operated rats, but plasma levels of ET-1 did not differ between them. Plasma ET-1 levels in genetically hypertensive rats (SHR and stroke-prone SHR) were significantly lower than those in age-matched normotensive Wistar-Kyoto (WKY) rats. The plasma concentrations of big ET-1, a precursor of ET-1, in both SHR and SHR-SP were significantly lower than those of WKY, suggesting that the production of ET-1 is decreased in rats of genetic hypertension. Although the vascular reactivity to ET-1 increased in both DOCA-salt hypertensive and genetically hypertensive rats, present findings of the plasma ET-1 levels suggest that the role of ET-1 in the vascular control system may be different in DOCA-salt hypertensive rats and genetically hypertensive rats.     

Abnormal regulation of the sympathoadrenal system in deoxycorticosterone acetate-salt hypertensive rats

With the use of circulating norepinephrine (NE) and epinephrine (E) levels, the sympathoadrenal activity as well as its local modulation by adrenoceptors were studied in normotensive (NT) and DOCA-salt hypertensive (HT) rats. In anesthetized hypertensive rats, plasma NE levels were higher, whereas in conscious animals both NE and E levels were found to be increased, suggesting an increased basal sympathoadrenal tone in these animals. The finding of a close correlation between blood pressure levels and NE levels suggests that the elevation of blood pressure may be linked to sympathetic system activity in this experimental model of hypertension. The reactivity of the sympathoadrenal system was also found to be increased in DOCA HT rats. Following a bilateral carotid occlusion of 1 min, which specifically activates the adrenal medulla, the elevation of E levels was found to be potentiated in intact or vagotomized HT rats. Moreover, in response to prolonged or acute hypotension in anesthetized and conscious animals, the elevation in plasma NE and E levels was found to be markedly potentiated in DOCA HT rats. The local modulating adrenoceptor-mediated mechanisms of the sympathoadrenal system appeared to be altered in this model of hypertension. Although it was possible to demonstrate that the E response to carotid occlusion can be greatly potentiated by administration of an alpha2-antagonist (yohimbine) and completely abolished by an alpha2-agonist (clonidine) in NT rats, the E response was found to be unaffected by the same treatments in HT rats, suggesting a reduced sensitivity in the alpha2-mediated inhibitory modulation of the adrenal medulla. Moreover, the acute treatment with a beta-blocker (sotalol) lowered circulating NE levels and blood pressure only in HT rats, suggesting the possibility of a more sensitive beta-receptor-mediated presynaptic facilitatory mechanism on sympathetic fibers of these animals. Finally, it was observed that the functional balance which exists between the activities of sympathetic fibers and the adrenal medulla in normotensive animals appears to be impaired in DOCA HT rats. In conclusion, the present studies suggest that the increased sympathoadrenal tone and reactivity may be due, in part, to a variety of dysfunctions in local adrenoceptor modulatory mechanisms of the sympathoadrenal system in DOCA hypertensive rats.     

Increased reactive oxygen species contributes to kidney injury in mineralocorticoid hypertensive rats.

Hypertension is associated with increased reactive oxygen species (ROS). Renal ROS production and their effects on renal function have never been investigated in mineralocorticoid hypertensive rats. In this study we hypothesized that increased ROS production in kidneys from deoxycorticosterone (DOCA)-salt rats contributes to adverse renal morphological changes and impaired renal function in DOCA-salt hypertensive rats. We also determined whether ROS-induced renal injury was dependent on blood pressure. DOCA-salt hypertensive rats exhibited a marked increase in blood pressure, renal ROS production, glomerular and tubular lesions, and microalbuminuria compared to sham rats. Treatment of DOCA-salt hypertensive rats with apocynin for 28 days resulted in attenuation of systolic blood pressure and improvement of renal morphology. Renal superoxide level in DOCA-salt rats was 215% of sham-operated rats and it was significantly decreased to 140% with apocynin treatment. Urinary protein level was decreased from 27 +/- 3 mg/day in DOCA-salt hypertensive rats to 9 +/- 2 mg/day. 28 days of Vitamin E treatment also reduced renal injury in regard to urinary protein level and renal morphology but had no effect on blood pressure in DOCA-salt rats. Increased urinary 8-isoprostane, a marker for oxidative stress, in DOCA-salt hypertensive rats (55 +/- 8 ng/day) was diminished by vitamin E treatment (24 +/- 6 ng/day). These data suggest that renal injury characteristic of mineralocorticoid hypertension is associated with oxidative stress and is partly independent of blood pressure.     

A fast-acting humoral factor mediates pressor hyperresponsiveness in deoxycorticosterone-salt rabbits

Six rabbits were sham operated and were given water to drink (sham-water group); six additional rabbits were sham operated and were given saline to drink (sham-salt group); another six rabbits received an implant of deoxycorticosterone (DOCA) and were given water to drink (DOCA-water group); a final group of six rabbits received implants of DOCA and were given saline to drink (DOCA-salt group). Two weeks later, all four groups of rabbits had approximately the same mean arterial pressures, and the sham-salt, DOCA-water, and DOCA-salt groups all had plasma renin activity values less than the sham-water group. The DOCA-salt group had greater pressor responses to norepinephrine (NE) at several doses than did the other three groups of rabbits. In another group of six sham-water and six DOCA-salt rabbits, measurements of cardiac output before and during infusions of NE at 800 ng/min/kg body wt revealed no changes in cardiac output before or during NE infusion, but the DOCA-salt group had significantly greater increases in mean arterial pressure and total peripheral resistance during NE than did the sham-water group. In another group of six DOCA-salt rabbits, the pressor response to several doses of NE were determined during infusion of the angiotensin II (AII) antagonist, [Sar1, Ile8] AII; this AII antagonist failed to alter the enhanced pressor responses to NE. A final experiment examined pressor responses to NE in six normal rabbits before and after cross circulation of blood with six DOCA-salt rabbits. After blood cross circulation the normal rabbits had exaggerated pressor responses to NE at 5, 15, and 30 min, but not at 60 min. Similar cross-circulation experiments between six pairs of normal rabbits did not show any transfer of pressor hyperresponsiveness. These studies indicated that pressor and vascular hyperresponsiveness in DOCA-salt rabbits is conveyed by a fast-acting hormonal factor and that AII probably is not involved in mediating this hyperresponsiveness.     

Mechanism of the anti-hypertensive property of the naturally occurring phenolic,malabaricone C in DOCA-salt rats

In this study, we studied whether chronic oral administration of the natural antioxidant, malabaricone C (mal C) can reduce blood pressure (BP) and attenuate cardio-vascular remodeling in deoxycorticosterone acetate (DOCA)-salt hypertensive rats. The dose of mal C for its anti-hypertensive action was optimized by measuring the systolic BP (SBP). DOCA-salt rats showed very high SBP, associated with organ hypertrophy, collagen depositions, and inflammatory infiltrations in cardiac and aortic sections, reduced plasma total antioxidant status and NO level, and increased levels of TBARS, PGI2 as well as vasoconstrictors (AVP, Big ET, and ET-1). DOCA-salt also reduced smooth muscle- and endothelium-dependent vascular relaxation in rats. Mal C reversed all these changes of the DOCA-salt rats and improved their vascular reactivity. Mal C exerts anti-hypertensive property in DOCA-salt rats by reducing oxidative stress and organ hypertrophy, and improving endothelial and vascular functions. Given that mal C has appreciable natural abundance and is non-toxic to rodents, further studies would help in establishing its medicinal potential against hypertension.     

TNF-alpha inhibition reduces renal injury in DOCA-salt hypertensive rats

Studies suggest that the inflammatory cytokine TNF-alpha plays a role in the prognosis of end-stage renal diseases. We previously showed that TNF-alpha inhibition slowed the progression of hypertension and renal damage in angiotensin II salt-sensitive hypertension. Thus, we hypothesize that TNF-alpha contributes to renal inflammation in a model of mineralocorticoid-induced hypertension. Four groups of rats (n = 5 or 6) were studied for 3 wk with the following treatments: 1) placebo, 2) placebo + TNF-alpha inhibitor etanercept (1.25 mg.kg(-1).day(-1) sc), 3) deoxycorticosterone acetate + 0.9% NaCl to drink (DOCA-salt), or 4) DOCA-salt + etanercept. Mean arterial blood pressure (MAP) measured by telemetry increased in DOCA-salt rats compared with baseline (177 +/- 4 vs. 107 +/- 3 mmHg; P < 0.05), and TNF-alpha inhibition had no effect in the elevation of MAP in these rats (177 +/- 8 mmHg). Urinary protein excretion significantly increased in DOCA-salt rats compared with placebo (703 +/- 76 vs. 198 +/- 5 mg/day); etanercept lowered the proteinuria (514 +/- 64 mg/day; P < 0.05 vs. DOCA-salt alone). Urinary albumin excretion followed a similar pattern in each group. Urinary monocyte chemoattractant protein (MCP)-1 and endothelin (ET)-1 excretion were also increased in DOCA-salt rats compared with placebo (MCP-1: 939 +/- 104 vs. 43 +/- 7 ng/day, ET-1: 3.30 +/- 0.29 vs. 1.07 +/- 0.03 fmol/day; both P < 0.05); TNF-alpha inhibition significantly decreased both MCP-1 and ET-1 excretion (409 +/- 138 ng/day and 2.42 +/- 0.22 fmol/day, respectively; both P < 0.05 vs. DOCA-salt alone). Renal cortical NF-kappaB activity also increased in DOCA-salt hypertensive rats, and etanercept treatment significantly reduced this effect. These data support the hypothesis that TNF-alpha contributes to the increase in renal inflammation in DOCA-salt rats.     

Influences of age and ovarian follicular reserve on estrous cycle patterns, ovulation, and hormone secretion in the Long-Evans rat

This study examined the influences of aging and reduced ovarian follicular reserve on estrous cyclicity, estradiol (E(2)) production, and gonadotropin secretion. Young virgin and middle-aged (MA) retired breeder female rats were unilaterally ovariectomized (ULO) or sham operated (control). Unilateral ovariectomy of young rats reduced the ovarian follicular reserve by one-half, to a level similar to that found in MA controls. Unilateral ovariectomy of MA females reduced the follicular pool further, to one half of MA controls. The incidence of regular cyclicity was significantly lower in MA ULO females than in young controls, with intermediate cycle frequency in young ULO and MA controls. Among cyclic rats, the magnitude of the proestrous LH surge was highest in young controls, intermediate in young ULO rats and MA controls, and lowest in MA ULO females. Similarly, ovulation rates were highest in young controls, intermediate in young ULO rats and MA controls, and lowest in MA ULO females. While young ULO rats exhibited augmented secondary FSH surges on estrous morning, middle-aged ULO females displayed secondary FSH levels comparable to young controls. The effects of age and reduced follicle number on estrous cyclicity and gonadotropin secretion were not due to altered E(2) secretion, as preovulatory E(2) levels were similar among all groups. Thus, experimental reduction in the follicular reserve exerts acute effects on the preovulatory LH surge, ovulation rate, and estrous cyclicity in both young and MA rats. However, decreased follicle number increases FSH levels only in young rats, indicating aging-related alterations in the feedback regulation of FSH.     

内源性CO对内皮素促大鼠主动脉平滑肌细胞增殖及MAPK活性的影响

血红素加氧酶（ｈｅｍｅ ｏｘｙｇｅｎａｓｅ,ＨＯ）是血红素分解代谢过程中的限速酶,它能使细胞内的血红素降解成胆绿素和一氧化碳（ｃａｒｂｏｎｍｏｎｏｘｉｄｅ,ＣＯ）,近来资料表明内源性一氧化碳对生理和病理状态下的血管张力有重要的调节作用,目前尚不不禁内源性ＨＯ／ＣＯ刘否参与平滑肌细胞增殖过程的调节,本实验在体内培养的大鼠主动脉平滑肌细胞模型上,用血色素加氧酶抑制剂卟啉锌－９（ｚｉｎｃ ｐｒｏｔｏｐｏ     

Polyphenols restore endothelial function in DOCA-salt hypertension: role of endothelin-1 and NADPH oxidase

Red wine polyphenols (RWPs) have been reported to exert beneficial effects in preventing cardiovascular diseases, such as hypertension. We studied the effects of chronic treatment with RWPs and apocynin, an inhibitor of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, on blood pressure, endothelial function, and oxidative status in deoxycorticosterone acetate (DOCA)-salt-induced hypertension. Rats were administered RWPs (40 mg/kg) or apocynin (33 microg/kg) daily by gavage for 5 weeks. Plasma catechin levels were detected only after RWP treatment. RWPs and apocynin prevented both the increase in systolic blood pressure and the proteinuria induced by DOCA-salt. Plasma malonyldialdehyde levels, urinary iso-prostaglandin F(2alpha) excretion, aortic superoxide production, and aortic NADPH oxidase activity were found to be increased in animals of the DOCA group. RWP and apocynin treatments reduced these parameters in DOCA-salt rats, having no effect on control rats. However, only RWPs reduced the increase in plasma endothelin-1 (ET-1) levels and aortic p22(phox) gene overexpression found in DOCA-salt animals. RWPs and apocynin also improved the blunted endothelium-dependent relaxation response to acetylcholine in noradrenaline-precontracted aortic rings. All these results suggest that chronic treatment with RWPs prevents hypertension and vascular dysfunction. RWPs prevent vascular oxidative stress by inhibiting NADPH oxidase activity and/or by reducing ET-1 release.     

Morphological and biochemical characterization of remodeling in aorta and vena cava of DOCA-salt hypertensive rats

Arterial remodeling occurs in response to mechanical and neurohumoral stimuli. We hypothesized that veins, which are not exposed to higher pressures in hypertension, would demonstrate less active remodeling than arteries. We assessed remodeling with two standard measures of arterial remodeling: vessel morphometry and the expression/function of matrix metalloproteinases (MMPs). Thoracic aorta and vena cava from sham normotensive and DOCA-salt hypertensive rats (110 +/- 4 and 188 +/- 8 mmHg systolic blood pressure, respectively) were used. Wall thickness was increased in DOCA-salt vs. sham aorta (301 +/- 23 vs. 218 +/- 14 mum, P < 0.05), as was medial area, but neither measure was altered in the vena cava. The aorta and vena cava expressed the gelatinases MMP-2, MMP-9, transmembrane proteinase MT1-MMP, and tissue inhibitor of metalloproteinase-2 (TIMP-2). Immunohistochemically, MMP-2 localized to smooth muscle in the aorta and densely in endothelium/smooth muscle of the vena cava. Western and zymographic analyses verified that MMP-2 was active in all vessels and less active in the vena cava than aorta. In hypertension, MMP-2 expression and activity in the aorta were increased (59.1 +/- 3.7 and 74.5 +/- 6.1 units in sham and DOCA, respectively, P < 0.05); similar elevations were not observed in the vena cava. MMP-9 was weakly expressed in all vessels. MT1-MMP was expressed by the aorta and vena cava and elevated in the vena cava from DOCA-salt rats. TIMP-2 expression was significantly increased in the aorta of DOCA rats compared with sham but was barely detectable in the vena cava of sham or DOCA-salt hypertensive rats. These findings suggest that large veins may not undergo vascular remodeling in DOCA-salt hypertension.     

Eucapnic intermittent hypoxia augments endothelin-1 vasoconstriction in rats: role of PKCdelta

We reported previously that simulating sleep apnea by exposing rats to eucapnic intermittent hypoxia (E-IH) causes endothelin-dependent hypertension and increases constrictor sensitivity to endothelin-1 (ET-1). In addition, augmented ET-1-induced constriction in small mesenteric arteries (sMA) is mediated by increased Ca(2+) sensitization independent of Rho-associated kinase. We hypothesized that exposing rats to E-IH augments ET-1-mediated vasoconstriction by increasing protein kinase C (PKC)-dependent Ca(2+) sensitization. In sMA, the nonselective PKC inhibitor GF-109203x (3 microM) significantly inhibited ET-1-stimulated constriction in E-IH arteries but did not affect ET-1-stimulated constriction in sham arteries. Phospholipase C inhibitor U-73122 (1 microM) also inhibited constriction by ET-1 in E-IH but not sham sMA. In contrast, the classical PKC (cPKC) inhibitor G?-6976 (1 microM) had no effect on ET-1-mediated vasoconstriction in either group, but a PKCdelta-selective inhibitor (rottlerin, 3 microM) significantly decreased ET-1-mediated constriction in E-IH but not in sham sMA. ET-1 increased PKCdelta phosphorylation in E-IH but not sham sMA. In contrast, ET-1 constriction in thoracic aorta from both sham and E-IH rats was inhibited by G?-6976 but not by rottlerin. These observations support our hypothesis that E-IH exposure significantly increases ET-1-mediated constriction of sMA through PKCdelta activation and modestly augments ET-1 contraction in thoracic aorta through activation of one or more cPKC isoforms. Therefore, upregulation of a PKC pathway may contribute to elevated ET-1-dependent vascular resistance in this model of hypertension.     

Plasma norepinephrine and heart rate dynamics during recovery from submaximal exercise in man

The time course of heart rate (HR) and venous blood norepinephrine concentration [NE], as an expression of the sympathetic nervous activity (SNA), was studied in six sedentary young men during recovery from three periods of cycle ergometer exercise at 21% +/- 2.8%, 43% +/- 2.1% and 65% +/- 2.3% of VO2max respectively (mean +/- SE). The HR decreased mono-exponentially with tau values of 13.6 +/- 1.6 s, 32.7 +/- 5.6 s and 55.8 +/- 8.1 s respectively in the three periods of exercise. At the low exercise level no change in [NE] was found. At medium and high exercise intensity: (a) [NE] increased significantly at the 5th min of exercise (delta [NE] = 207.7 +/- 22.5 pg.ml-1 and 521.3 +/- 58.3 pg.ml-1 respectively); (b) after a time lag of 1 min [NE] decreased exponentially (tau = 87 s and 101 s respectively); (c) in the 1st min HR decreased about 35 beats.min-1; (d) from the 2nd to 5th min of recovery HR and [NE] were linearly related (100 pg.ml-1 delta [NE] congruent to 5 beats.min-1). In the 1st min of recovery, independent of the exercise intensity, the adjustment of HR appears to have been due mainly to the prompt restoration of vagal tone. The further decrease in HR toward the resting value could then be attributed to the return of SNA to the pre-exercise level.