摘要:

Because nitric oxide inhibits the synthesis and vasoconstrictor effect of endothelin-1, the effect of endothelin-1 may be enhanced under conditions of chronic inhibition of nitric oxide synthesis. We studied the effect of chronic therapy with bosentan, a combined endothelin-A/endothelin-B receptor antagonist, on blood pressure and vascular function and structure of small arteries as well as on the reactivity of the aorta in Nomega-nitro-L-argininemethyl ester (L-NAME)-induced hypertension. Six-week-old Wistar-Kyoto rats were randomly treated for 6 weeks with placebo (control), L-NAME (70 mg/kg per day), or L-NAME plus bosentan (100 mg/kg per day). The treatments were stopped 2 to 3 days before the in vitro experiments so that only the long-term effects of the drugs could be observed. L-NAME increased systolic blood pressure; bosentan did not prevent this effect although the initial blood pressure rise was delayed (P = NS versus L-NAME group). Bosentan administration did not modify the structural alteration of the resistance vessels induced by L-NAME, nor did it improve endothelium-dependent relaxation of resistance vessels or the aorta. However, bosentan therapy markedly increased endothelium-dependent contraction to acetylcholine, which was slightly enhanced by L-NAME. In contrast, bosentan inhibited aortic endothelium-dependent contractions when applied acutely in vitro. This observation, together with the increased maximal vasoconstriction to the thromboxane A2receptor agonist U46619 after 2 weeks of bosentan administration, suggests that bosentan also interacts with the receptors mediating endothelium-dependent contractions. In conclusion, our experiments suggest a minor role of endothelin in chronic L-NAME-induced hypertension as well as in the concomitant alterations of vascular structure. (Hypertension. 1997;29:763-769.)

ISSN:0194-911X    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Cardiovascular complications are a well-known feature of chronic renal failure. Increased wall thickness of intramyocardial arterioles and elastic (aorta) and peripheral (mesenteric) arteries is seen even after normalization of blood pressure. It is currently unknown whether such increases result from hyperplasia of vascular smooth muscle cells, hypertrophy, or a combination of both or from an increase in aortic extracellular matrix. Using a recently developed unbiased stereological technique (the dissector), we investigated the aortas of subtotally nephrectomized rats and sham-operated controls after perfusion fixation. We determined aortic wall thickness, cross-sectional area of aortic media, total number of vascular smooth muscle cells per unit aortic length (1 mm), mean cell and nuclear volumes, volume density of elastic fibers, extracellular matrix, vascular smooth muscle cells, and total volumes of these structures per unit of aortic length (1 mm). Blood pressure was not significantly increased in subtotally nephrectomized rats. In contrast, wall thickness, cross-sectional media, total number of aortic vascular smooth muscle cells, and volume of extracellular matrix including collagen were significantly increased after subtotal nephrectomy, whereas cellular hypertrophy was only modest and an increase in elastic fibers did not occur. In conclusion, increased aortic wall thickness in experimental renal failure results primarily from an increase in aortic extracellular matrix. In addition, however, proliferation of aortic vascular smooth muscle cells resulting in cell hyperplasia also contributed to aortic wall thickening to a minor degree. It appears that aortic wall thickening is caused by secretory stimulation of the proliferating vascular smooth muscle cells, resulting in increased matrix production. The nature of the underlying stimulus requires further investigation. (Hypertension. 1997;29:770-775.)

ISSN:0194-911X    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Whereas the protein product of the Bcl-2 gene inhibits apoptosis, the protein product of the Bax gene acts as a promoter of apoptosis. To gain insight into the regulation of apoptosis in vascular smooth muscle cells in arterial hypertension, we investigated the expression of the proteins Bcl-2 and Bax in small intramyocardial arteries of 36-week-old normotensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR). In addition, 16-week-old SHR were treated for 20 weeks with the angiotensin-converting enzyme inhibitor quinapril and killed at 36 weeks of age. We measured the percentages of smooth muscle cells expressing these proteins using monoclonal antibodies and the avidin-biotin immunoperoxidase method. Compared with WKY, untreated SHR exhibited increased (P < .001) Bcl-2 expression and similar Bax expression. Values of Bcl-2 measured in quinapril-treated SHR were significantly lower than values measured in untreated SHR and similar to values measured in WKY. Quinapril-treated SHR showed higher (P < .001) Bax expression than WKY and untreated SHR. Bcl-2 expression was directly correlated with systolic pressure. Inverse correlations were found between the expression of Bax and the activities of both cardiac and circulating angiotensin-converting enzyme. These findings suggest that smooth muscle cell apoptosis might be inhibited in small arteries of adult SHR as a consequence of an excess of the protein Bcl-2. In addition, our results suggest that chronic angiotensin-converting enzyme inhibition might restore the susceptibility to apoptosis in these cells through stimulation of the protein Bax. (Hypertension. 1997;29:776-780.)

ISSN:0194-911X    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

We studied structural and functional changes of small muscular arteries from the mesenteric vascular bed of young spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY) using a new morphometric protocol involving the use of confocal microscopy and a pressurized artery system. At 3 and 4 weeks of age, systolic pressure of SHR and WKY was similar; however, significant structural changes in the mesenteric vasculature were already present in SHR. Arteries fixed under pressure in vitro from SHR had a larger medial volume and increased number of smooth muscle cell layers but similar lumen size compared with arteries from WKY in maximally relaxed conditions. Functional studies showed that SHR arteries contracted more in response to stimulation by KCl and norepinephrine, resulting in a significantly smaller lumen size in these vessels than in those from WKY. SHR arteries precontracted with KCl were also able to maintain a smaller lumen diameter than WKY arteries when challenged with increasing pressure levels. No difference in the sensitivity of response of these arteries to norepinephrine stimulation was found. At 3 and 4 weeks of age, mesenteric arteries from some SHR and WKY were not responsive to periarterial nerve stimulation, and the number of responders was higher in the WKY than SHR. However, a greater degree of contraction was found in SHR arteries responding to field stimulation at 4 weeks than in WKY arteries. We conclude that there is a temporal difference in the rate of functional maturation of the innervation in SHR arteries compared with WKY arteries. Structural changes of the small muscular arteries, caused by an increase in the medial volume, and increased number of smooth muscle cell layers are primary changes that contribute to the development of hypertension in the SHR because these changes are present at the age when blood pressure is similar in SHR and WKY. (Hypertension. 1997;29:781-789.)

ISSN:0194-911X    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Recently, heme oxygenase-1 (HO-1) has been shown to be present in vascular smooth muscle cells. In the present study, we examined the effect of angiotensin II (Ang II) on HO-1 in rat vascular smooth muscle cells. After treatment with 100 nmol/L Ang II, HO-1 mRNA levels were decreased, with a nadir at 2 hours (39 +/- 9% of the control level, P < .01). This downregulation was completely blocked by the Ang II type 1 receptor antagonist losartan. Western blot analysis showed that HO-1 protein is also significantly downregulated, with a nadir at 4 hours (52 +/- 6% of the control level, P < .01). Heme oxygenase activity was also significantly decreased at 4 hours (control, 0.35 +/- 0.86 nmol bilirubin/mg per hour; Ang II, 0.10 +/- 0.06). This downregulation was observed in serum-starved cells to a similar extent as in serum-supplemented cells. Inhibitors of protein kinase C, lipoxygenase, cyclooxygenase, cytochrome P450 monooxygenase, and phospholipase A2did not block this downregulation. However, this effect was not observed in the absence of calcium and presence of EGTA (2 mmol/L). Furthermore, a 2-hour incubation with calcium ionophore or arginine vasopressin decreased HO-1 mRNA levels, suggesting that an increase of intracellular calcium mediates the downregulation. In conclusion, Ang II decreases HO-1 mRNA in a calcium-dependent manner in vascular smooth muscle cells, which may provide a novel mechanism for the modulation of vascular tone and oxidative stress. (Hypertension. 1997;29:790-795.)

ISSN:0194-911X    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

We have previously shown that the vasopressor effect of angiotensin II (Ang II) is inhibited by lipoxygenase (LO) blockers. To elucidate the specific mechanism involved, we studied the relationship between the contractile effect of Ang II and LO products in a human placental preparation. In perfused placental cotyledons, Ang II (boluses of 1 to 10 micro gram) increased perfusion pressure and 12-hydroxyeicosatetraenoic acid (12-HETE) release. The LO blockers phenidone and n-propyl gallate reduced the maximal Ang II-induced increment in pressure from 26 +/- 3 to 16 +/- 3 and 18 +/- 4 mm Hg, respectively (P < .05 for both). Ang II alone (10 micro gram) increased 12-HETE release from 8.9 +/- 3.6 to 37.6 +/- 0.4 ng/min, and this rise was entirely blocked by both phenidone and n-propyl gallate. Pressure increase generated by an increase in flow rate had no effect on 12-HETE formation. In deendothelialized umbilical artery segments, Ang II (10-7mol/L) increased 12-HETE formation by 47 +/- 5% (n = 20). In cultured umbilical artery smooth muscle cells, Ang II increased 12-HETE formation from 48.1 +/- 7.2 to 75.1 +/- 15.3 ng/mg protein, and this effect was also blocked by the specific LO inhibitor baicalein (10-6mol/L). These results provide evidence that the vasopressor effect of Ang II is functionally coupled to 12-LO activation, which apparently takes place in arterial smooth muscle cells. (Hypertension. 1997;29:796-801.)

ISSN:0194-911X    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Low sodium intake is the most widely used non-pharmacological approach to the treatment of hypertension. Although nonpharmacological treatment is by definition regarded as safe, the suggestion has been made that low sodium intake is not totally devoid of inconveniences, and animal data have shown it to be accompanied by an impairment of reflex blood pressure control and homeostasis. However, no data exist on this issue in humans. In mild essential hypertensive patients (age, 34.1 +/- 3.3 years [mean +/- SEM]), we measured beat-to-beat arterial blood pressure (finger photoplethysmographic device), heart rate (electrocardiogram), and efferent postganglionic muscle sympathetic nerve activity (microneurography) at rest and during baroreceptor stimulation and deactivation, induced by stepwise intravenous infusions of phenylephrine and nitroprusside, respectively. Measurements were performed at the end of three dietary periods, ie, after 8 days of regular sodium intake (210 mmol NaCl/d), low sodium intake (20 mmol NaCl/d) with unchanged potassium intake, and again regular sodium intake. Compared with the initial regular sodium diet, low sodium intake reduced urinary sodium excretion, whereas urinary potassium excretion was unchanged. Systolic blood pressure was significantly (P < .05), although slightly, reduced, whereas diastolic blood pressure was unaffected. Muscle sympathetic nerve activity was increased by 23.1 +/- 5.2% (P < .05). The increase was accompanied by a clear-cut impairment of the baroreceptor ability to modulate muscle sympathetic nerve activity, ie, by a 43.9 +/- 5.7% (P < .01) reduction in the sensitivity of the baroreceptor-muscle sympathetic nerve activity reflex compared with the control condition. Baroreceptor modulation of heart rate was also impaired, although to a smaller and less consistent extent. When regular sodium intake was restored, all the above-mentioned parameters and baroreflex responses returned to the values observed at the initial regular sodium diet. These data raise evidence that in humans sodium restriction may impair the arterial baroreflex. This may be responsible for the sympathetic activation occurring in this condition and for the impairment of blood pressure homeostasis. (Hypertension. 1997;29:802-807.)

ISSN:0194-911X    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

In salt-sensitive hypertensive animal models and human subjects compared with their salt-resistant counterparts, sympathetic activity is abnormally enhanced during a high salt diet. We examined whether salt loading differentially modulates the arterial baroreceptor reflex (ABR), a major control mechanism of arterial pressure and sympathetic vasomotor activity, in young normotensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR). Six-week-old WKY and SHR were fed a normal (0.66%) or high (8.00%) salt diet for 4 weeks. After the diet regimen, baseline levels of mean arterial pressure (MAP), renal sympathetic nerve activity (RSNA), and the overall and central properties of the ABR were compared among the four groups of rats under halothane anesthesia. In WKY, a high salt diet did not affect baseline arterial pressure and RSNA but potentiated the ABR, as evidenced by an increase in the maximal slope of MAP-RSNA and MAP-heart rate relationships. In SHR, by contrast, salt loading accelerated hypertension and sympathetic overactivity and impaired the ABR. Salt-induced modulation of the ABR was associated with that of the central property, since reflex inhibition of RSNA by stimulation of the aortic depressor nerve was augmented in WKY and attenuated in SHR. These results suggest that differential modulation of the central mechanism subserving the baroreflex control of sympathetic activity at least partly accounts for the difference in salt sensitivity between WKY and SHR. (Hypertension. 1997;29:808-814.)

ISSN:0194-911X    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

We have isolated a labile, specific sodium pump inhibitor or digitalis-like factor from the peritoneal dialysate of volume-expanded renal failure patients whose levels correlated closely with volume status and blood pressure. This study characterizes the inhibitory profile of this agent compared with that of ouabain against the three alpha-isoforms of the sodium pump. We prepared microsomal Na,K-ATPase from rat tissues representing the highest proportion of one of the alpha-isoforms. Both Northern and Western blot analyses confirmed that kidney had predominantly the alpha1-isoform, skeletal muscle the alpha2-isoform, and fetal brain the alpha3-isoform. Ouabain (5 x 10-6mol/L) produced little inhibition of kidney Na,K-ATPase (3.4 +/- 2.0%) but significant inhibition of skeletal muscle (37.2 +/- 3.7%, P < .001) and fetal brain (38.8 +/- 3.5%, P < .001) activity. In contrast, the labile digitalis-like factor, causing comparable inhibition of fetal brain Na,K-ATPase activity (33.3 +/- 4.7%), produced markedly greater inhibition of kidney (42.5 +/- 5.6%, P < .001) and moderately greater inhibition of skeletal muscle pump activity (57.7 +/- 6.3%, P < .05). In addition, the labile digitalis-like factor produced a marked concentration-dependent inhibition of the alpha2- and alpha3-isoforms (r = .79, P = .00005). Experiments combining the labile digitalis-like factor and ouabain confirmed that digitalis-like factor, unlike ouabain, was an effective inhibitor of all three isoforms in rat, in particular alpha2. The different pattern of isoform sensitivity displayed by the labile digitalis-like factor and ouabain further differentiates the two agents and raises some interesting possibilities about the functional implications of the endogenous factor. (Hypertension. 1996;29:815-821.)

ISSN:0194-911X    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Arterial hypertension, nephrotoxicity, and magnesium loss are common side effects of the immunosuppressive agent cyclosporin A (CsA). In the present study, the effects of dietary sodium and magnesium on CsA toxicity were examined in spontaneously hypertensive rats. A 6-week treatment with CsA during a moderately low-sodium diet (Na 0.3%, Mg 0.2% of the dry weight of the chow) raised blood pressure only slightly, without evidence of nephrotoxicity. By contrast, CsA during a high-sodium diet (Na 2.6%) produced a pronounced rise in blood pressure as well as marked nephrotoxicity, comprising decreased creatinine clearance, increased levels of serum creatinine and urea, and increased urinary protein excretion. During the high-sodium diet, CsA decreased myocardial and bone magnesium concentration and increased myocardial and renal calcium concentration. Magnesium supplementation (Mg 0.6%) protected against the CsA-induced hypertension and nephrotoxicity during the high-sodium diet. Magnesium supplementation also completely prevented the CsA-induced myocardial magnesium depletion and calcium accumulation in the heart and kidney during the high-sodium diet. Our findings indicate a detrimental interaction between increased sodium intake and CsA treatment and a marked protection by concomitant oral magnesium supplementation. (Hypertension. 1997;29:822-827.)

ISSN:0194-911X    

出版商:OVID    

年代:1997

数据来源: OVID