Differential regulation of nitric oxide synthases and their allosteric regulators in heart and vessels of hypertensive rats.

OBJECTIVE: Nitric oxide synthase (NOS)-derived nitric oxide (NO) production is regulated posttranslationally through enzyme's inhibitory interaction with the caveolar coat protein, caveolin and stimulatory interaction with the chaperone heat shock protein, Hsp90. However, changes in the expression of these regulators with the development of hypertrophic cardiomyopathy are unknown. METHODS: Histochemical and immunoblotted signals for the NOS isoforms, caveolin and Hsp90 were compared in left ventricle (LV) and aortic or mesenteric vessels between spontaneously hypertensive rats (SHR; 18 and 63 weeks old) and age-matched normotensive Wistar-Kyoto (WKY) rats. To assess functional impacts on downstream NO signaling, superoxide anions (O(2)(-)) and cGMP contents were measured in the same tissues by oxidative fluorescent hydroethidine staining and enzyme immunoassay, respectively. RESULTS: Compared with levels in age-matched WKY rats, endothelial NOS (eNOS) proteins were increased in aorta of SHR at 18 weeks. Conversely, aortic caveolin-1 and -3 were decreased in SHR, whereas Hsp90 remained unchanged. In LV tissue of SHR at 18 weeks, caveolin-1 and -3 were similarly decreased, but Hsp90 upregulated, together with a downregulation of eNOS. However, at 63 weeks, both eNOS and neuronal NOS (nNOS) were markedly upregulated in the LV of SHR, together with an upregulation of Hsp90. No difference in cardiac and aortic cGMP contents was found between the two strains. In LV sections, O(2)(-) generation was higher in older compared with younger rats from both strains and highest in 63 weeks SHR. CONCLUSIONS: Changes in NOS protein abundance in SHR rats compared with WKY controls are differentially regulated according to the age of hypertension and the tissue examined and are not necessarily correlated with cGMP contents. The coordinate expressional changes in NOS isoforms and their allosteric regulators, such as caveolin and Hsp90, may act as a compensatory mechanism to maintain the production of bioactive NO in the face of increased oxidant stress.

Chronic hydroxymethylglutaryl coenzyme a reductase inhibition and endothelial function of the normocholesterolemic rat: comparison with angiotensin-converting enzyme inhibition.

Hydroxymethylglutaryl coenzyme A (HMG-CoA) reductase inhibitors seem to have clinical benefits beyond those predicted by their lipid-lowering action. The objective was to evaluate the vascular effect of long-term treatment with statins on isolated rat aorta and their ability to prevent the acute toxicity of oxidized low-density lipoproteins (oxLDLs) compared with angiotensin-converting enzyme (ACE) inhibitors. Four groups of Wistar rats were treated for 5 weeks. Group 1 received pravastatin 20 mg/kg/d orally; group 2 received atorvastatin 10 mg/kg/d; group 3 received ciprofibrate 25 mg/kg/d; and group 4 served as control. Total cholesterol and triglyceride plasma levels were not altered, except in group 3, in which both parameters were decreased. The inhibitory effect of the endothelium on serotonin-induced contractions was significantly increased in group 1. A significant leftward shift of the concentration-response curves to acetylcholine (1 nM-0.1 mM) was observed in group 1 but the maximal relaxation to acetylcholine was similar in the four groups. In contrast, in the presence of human Cu2+-oxLDL (300 microg/ml, 30 min of preincubation), the maximal relaxation to acetylcholine was markedly decreased (p < 0.02) in groups 3 and 4 versus that of groups 1 and 2. No difference in superoxide accumulation was observed by the chemiluminescence technique. Cyclic guanosine monophosphate (cGMP), measured by enzyme immunoassay in aortic tissues, was increased in group 1 in the presence of superoxide dismutase. Endothelial nitric oxide synthase (eNOS) expression was not altered (Western blot and enzyme-linked immunosorbent assay). In aortas isolated from a fifth group of rats treated with an ACE inhibitor (ramipril 10 mg/kg/d for 6 weeks), similar results to those of group 1 were observed except that the eNOS abundance was significantly enhanced. Thus, long-term statin treatment upregulates the eNOS pathway and attenuates the acute toxicity of human oxLDL. In contrast to chronic ACE inhibition, the eNOS abundance is not increased.