Atrial volume receptors: demostration of an effective threshold of left atrial distension by an inflated balloon to induced increased diuresis in the anesthetized dog

ABSTRACT

1. The intraatrial balloon technique was used to study the effect of distension of the left atrium on the urinary flow of anesthetized dogs. The ballon was inflated with 0.3, 0.4 or 0.5 ml saline/Kg weight, respectively, in three experimental groups, each containing 10 mongrel dogs. Intraatrial presssure, arterial blood pressure, ECG and respiratory excursions were continuously monitored in all experiments. Urine flow, inulin and p-aminohippuric acid clearance, urine osmolarity, total sodium and potassium excretion were measured during the control period, after inflation of the ballon and 30 min after deflation. 2. Left atrial distension with 0.3 ml/Kg caused essentially no increase in diuresis. Inflation with 0.4 ml/Kg induced a 60% increase of mean urinary flow with respect to the control period. Inflation with 0.5 ml/Kg elicited a meanincrease in diuresis of 110%. 3. When it occurred, increased ddiuresis was accompanied by a decrease of urine osmolarity that was compatible with a decrease of antidiuretic hormone activity, and by increase in total sodium excretion. there were no statistically significant changes in glomerular filtration rate and effective renal plasma flow. 4. The demonstration of a "threshold" for the distension of the atrium that is capable of inducing diuresis in the anesthetized dog aand of overcoming strong opposing hemodynamic effects provides additional indirect evidence for the role of the left atrial stretch receptors in the regulation of body fluid volume