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.