Atrial natriuretic peptide attenuates the reflex sympathetic responses to lower body negative pressure

The authors studied the effect of intravenous infusion of atrial natriuretic peptide (ANP) on the plasma catecholamine and forearm vasoconstrictor responses to cardiopulmonary baroreflex deactivation in six normal, male volunteers in order to determine whether ANP influences reflex forearm vasoconstriction in humans. Unloading of low-pressure cardiopulmonary baroreceptors (CPBR) was accomplished by application of low levels (-10 and -20 mm Hg) of lower body negative pressure (LBNP). The authors measured the plasma norepinephrine (NE) and epinephrine, the mean arterial pressure (MAP), and the forearm vascular resistance (FVR) responses to reflex sympathetic activation by LBNP. ANP infusion (0.1 microgram.kg-1.min-1) decreased (p less than 0.01) basal MAP, as well as plasma renin activity and plasma aldosterone levels (p less than 0.05). ANP infusion also reduced (p less than 0.01) plasma NE responses to both levels of LBNP and tended to decrease both epinephrine and FVR during ANP infusion at -20 mm Hg LBNP (p = 0.8). These data suggest that exogenous ANP inhibits the reflex sympathetic responses that occur with CPBR unloading. The blunted plasma NE responses to CPBR unloading parallel the attenuation of FVR response to LBNP during ANP infusion, despite significant LBNP-induced hypotension.