PRIMARY NEURAL INVOLVEMENT IN RENAL HEMODYNAMIC AND FUNCTIONAL-RESPONSES TO PROLONGED STIMULATION OF ATRIAL RECEPTORS IN ANESTHETIZED DOGS

To determine the precise contributory role of neural and humoral facto rs in the efferent mechanism of the atrial receptor-renal reflex, we h ave examined the effects of prolonged (45 min) stimulation of left atr ial receptors on renal haemodynamics and function simultaneously in bo th kidneys (right kidney intact and left kidney denervated) of anaesth etized dogs. Aortic pressure in these dogs was held constant by means of an arterial reservoir connected to the aorta; heart rate changes we re prevented by blocking beta(1)-adrenoceptor activity with atenolol ( 2 mg kg(-1) I.V.). Localized stimulation of atrial receptors in six do gs increased renal blood flow (6 +/- 2%), creatinine clearance (11 +/- 4%), urine flow (9 +/- 3%), sodium excretion (14 +/- 7%) and osmolal excretion (10 +/- 4%), and decreased free water clearance (14 +/- 7%) in intact kidneys, but led to no changes in denervated kidneys. In an additional four dogs, cooling the vagus nerves to 6-7 degrees C or cut ting them in the neck abolished the renal responses to stimulation of atrial receptors in these stabilized preparations. These data clearly demonstrate that the renal responses to prolonged stimulation of atria l receptors are primarily mediated via myelinated vagal afferents and renal sympathetic efferents.