Nitric oxide, atrial natriuretic factor, and dynamic renal autoregulation

Inhibition of nitric oxide (NO) synthase by N-omega-nitro-L-arginine methyl ester (L-NAME) increases arterial pressure (PA) and profoundly reduces renal blood flow (RBF). Here we report that L-NAME causes changes in the PA-RBF transfer function which suggest augmentation of the approximate to 0.2 Hz autoregulatory mechanism. Attenuation of PA fluctuations from 0.06 to 0.11 Hz was enhanced, indicating increased efficacy of autoregulation. Also, the rate of gain reduction between 0.1 and 0.2 Hz increased while the associated phase peak became greater than or equal to pi/2 radians, indicating emergence of a substantial rate-sensitive component in this system so that autoregulatory responses to rapid PA changes become more vigorous. Infusion of L-arginine partly reversed the pressor response to L-NAME, but not the renal vasoconstriction or the changes in the transfer function. The ability of atrial natriuretic factor (ANF), which also acts via cGMP, to replace NO was assessed. ANF dose dependently reversed but did not prevent the pressor response to L-NAME, indicating additive responses. ANF did not restore RBF or reverse the changes in the transfer function induced by L-NAME. The rate-sensitive component that was enhanced by L-NAME remained prominent, suggesting that either ANF did not adequately replace cGMP or provision of a basal level of cGMP was not able to replace cGMP generated in response to NO. It is concluded that NO synthase inhibition changes RBF dynamics with the most notable change being increased contribution by a rate-sensitive component of the myogenic system.