EFFECT OF SYMPATHECTOMY ON RENAL AND CIRCULATORY ACTION OF ATRIAL-NATRIURETIC-PEPTIDE

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-mu-g.kg-1.min-1) were compared with those to sodium nitroprusside (NP; 2 + 20-mu-g.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 > 0.05). The high dose of ANP increased urine flow by 43.2 +/- 7.2-mu-l.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.