Vagal mediation of the effects of atrial natriuretic factor on blood pressure and arterial baroreflexes in the rabbit

We investigated the hemodynamic effect of synthetic atrial natriuretic factor Auriculin A (ANF) and its influence on arterial baroreflex control of heart rate, systemic blood pressure, and perfusion pressure in the hind limb (perfused at constant flow) in rabbits anesthetized with alpha-chloralose and urethane. The neural mechanisms underlying these effects were also studied. In the intact animal, a 45-minute constant infusion of ANF (2 micrograms/kg prime, 0.2 microgram/kg/min) significantly reduced mean blood pressure and increased mean perfusion pressure, while heart rate did not change. Comparable data were obtained with lower (0.5 microgram/kg + 0.05 microgram/kg/min; 1 microgram/kg + 0.1 microgram/kg/min) or higher (4 micrograms/kg + 0.4 microgram/kg/min; 8 micrograms/kg + 0.8 microgram/kg/min) doses of ANF. In addition, ANF enhanced bradycardic reflex responses to phenylephrine i.v. bolus administration, while it did not change baroreflex-mediated responses to nitroglycerin i.v. bolus administration and to 30-second bilateral carotid occlusion. The specificity of the influence of ANF on arterial baroreflex responses was confirmed by the observation that no significant change in reflex responses to phenylephrine or carotid occlusion was detectable during a comparable decrease in blood pressure induced by a constant infusion of nitroglycerin. Bilateral vagotomy prevented both the fall in blood pressure and the increase in perfusion pressure induced by ANF, while cholinergic blockade (atropine, 0.5 mg/kg i.v.) or adrenergic blockade (propranolol, 0.3 mg/kg i.v. + phentolamine, 0.3 mg/kg i.v.) did not modify the hemodynamic response to ANF observed in the intact animal.(ABSTRACT TRUNCATED AT 250 WORDS)