Atrial natriuresis under the condition of a constant renal perfusion pressure: experiments on conscious dogs

An experimental elevation of left atrial pressure (eLAP) by means of a reversible mitral stenosis is accompanied with an increase in sodium excretion (UNaV) and arterial blood pressure (by about 20 mm Hg, 2.7 kPa), and by a decrease in plasma renin activity. It is well established that an increase in renal perfusion pressure (Pren) can augment UNaV. Therefore the present study was undertaken to examine whether the eLAP-induced natriuresis was caused by the increased Pren. -Four female beagle dogs were kept under controlled environmental conditions. They received a sodium rich diet (14.5 mmol/Na/kg/d). The dogs were chronically instrumented: purse string around the mitral annulus, catheter in the left atrium, carotid loop, pneumatic cuff above the renal arteries, pressure transducer below the renal arteries. Pren was kept constant by means of a digital servofeedback control circuit. The dogs served as their own controls (13 experiments without and 15 experiments with a controlled renal perfusion pressure were performed). After eLAP(+1.0 kPa), UNaV rose from 4.1 +/- 2.6 to 10.3 +/- 3.9 mumol Na/min/kg. If Pren was kept constant, the corresponding values were 4.2 +/- 2.8 and 9.3 +/- 2.9 mumol/min/kg. These data clearly indicate that the atrial natriuresis is not mediated by an augmentation of renal perfusion pressure. Therefore these results support the hypothesis that atrial natriuresis probably is due to en eLAP-induced suppression of the renin-angiotensin-system or other natriuretic mechanisms.