Effect of sympathectomy on renal and circulatory action of atrial natriuretic peptide

Abstract

Sympathetic nervous system (SNS) involvement in cardiovascular (CV) and renal actions of atrial natriuretic peptide (ANP) was examined in eight chronically instrumented rats. Responses to 90-min atriopeptin II infusion (0.03 then 0.3 micrograms.kg-1.min-1) were compared with those to sodium nitroprusside (NP; 2 + 20 micrograms.kg-1.min-1) before and after sympathectomy (SX) with 6-hydroxydopamine (6-OHDA). The NP-induced drop in blood pressure (BP) was greater after SX (-12 +/- 1% before vs. -24 +/- 2% after SX). In contrast, 6-OHDA altered (blunted) only the bradycardic response to high dose of ANP (-23 +/- 5% before vs. -3 +/- 4% after SX). The decreased BP (-18 +/- 1% before vs. -12 +/- 2% after), depressed cardiac output (CO; -29 +/- 1% before vs. -22 +/- 3% after), and elevated systemic vascular resistance (SVR; 16 +/- 2 vs. 16 +/- 6%) were unchanged (paired t test, P greater than 0.05). The high dose of ANP increased urine flow by 43.2 +/- 7.2 microliters.min-1.100 g body wt-1 and sodium excretion by 1.76 +/- 0.56 mu eq.min-1.100 g body wt-1 but had no effect after SX. These results suggest that while withdrawal of SNS activity contributes to the CO-lowering effect of ANP, it does not mediate its action to elevate SVR. Attenuation of the capacity for reflex sympathoexcitation by SX did not reveal a vasodilator action. The lack of response after SX suggests that ANP's renal excretory actions are mediated in part by withdrawal of SNS activity.