Angiotensin II Increases Enos Expression in the Rat Myocardium Independent of Pressor Effect.
There is accumulating evidence that nitric oxide antagonizes angiotensin II (AII) effects at multiple regulatory levels of the cardiovascular system. In the present study, we first determined the expression of endothelial (eNOS) and neuronal (nNOS) isoforms of nitric oxide synthase (eNOS) in the ventricles of two kidney Goldblatt(2K1C, 2 months) and L-NAME treated (LN, 2 months)hypertensive rats with Western blot. Systolic arterial pressures were 130±3, 165±4, 160±5 mmHg in control (n=7) and 2K1C (n=6)and LN treated (n=6) rats, respectively. nNOS was barely detected in ventricles of normotensive and 2K1C and LN hypertensive rats. In contrast, eNOS was detected in ventricles of all groups of rats and was increased by 100±8% and by 88±12%in 1K1C and LN rats. Experiments performed with blocking peptide (100:1; blocking peptide to antibody proportion) indicated that the ∼130 kDa bands identified in membranes blotted with anti-eNOS antibody was specific for eNOS. Another group of rats was continuously infused with AII (D1= 10, n=5; D2= 40, n=4 ng/kg/min) for 6 days and arterial pressure measured daily (1 h, continuous, sampled at 100 Hz). Arterial pressure did not change significantly during infusion of D1 and increased by 22±3 mmHg during D2 infusion. Both, D1 and D2 increased eNOS expression by ∼95% while, again, no change was observed in nNOS expression. These data indicate that 1) eNOS expression is up-regulated in 2K1C and LN hypertensive rats; 2) AII infusion enhances the eNOS expression by a level similar to that observed in 1K1C and LN hypertensive rats; and 3) The influence of AII on eNOS expression is independent of its pressor effect. In conclusion,our data suggest that AII increases the expression of eNOS, independent of the its hemodynamic effect and could be responsible for the increase in eNOS expression in 1K1C hypertensive rats. In addition, this modulation is specific for eNOS since nNOS is present only in small amounts in the rat myocardium and is not modulated by AII. The mechanism responsible for the increase in eNOS expression in LN rats is not clear, but could be related to a modulation mediated by a product derived from eNOS action on its substrate.