Role of Nitric Oxide in Responses to Renin-Angiotensin System Inhibition in Sodium-Depleted Guinea Pig and Rat

Abstract

Previous reports have suggested that NO is an important mediator of the antihypertensive effects of renin-angiotensin system (RAS) inhibition. We examined the effects of the NO synthase inhibitor L-NNA on the hypotensive effects of captopril, the Ang II antagonist EXP 3174, or the renin inhibitor terlakiren. In sodium-depleted guinea pigs (GPs), L-NNA (3 mg/kg) increased MAP by 15-21% for at least 5 hours. L-NNA partially blocked the hypotensive effects of captopril (1 mg/kg, iv), but not those of EXP 3174 (1 mg/kg, iv) or terlakiren (3 mg/kg). In sodium-depleted rats, 10 mg/kg L-NNA (iv) increased MAP by 16-22%, and partially or fully blocked the hypotensive effect of EXP 3174 (1 mg/kg, iv) or captopril (3 mg/kg, iv), respectively. Thus, in contrast to the rat, NO in GPs appears to participate only in the hypotensive action of ACE inhibition and does not appear to be strongly involved in the hypotensive action of AII antagonism or renin inhibition. The involvement of NO in the hypotensive effects of RAS antagonists other than ACE inhibitors may be species-dependent.

Inhibition of Nitric Oxide Synthase Activity Diminishes the Acute Effects of Relaxin on Growth, But Not Softening, of the Cervix in the Rat

“…Pfeiffer et al (30) provided evidence that L-NAME is rapidly hydrolyzed in whole blood to the potent and long-lasting inhibitor N-nitro-l-arginine (L-NNA). A bolus iv injection of as little as 10 mg/kg L-NNA (1/10th the dose of L-NAME used in this study) increased mean arterial pressure for at least 5 h in sodium-depleted rats (31).…”