Effect of reduced extracellular sodium concentration on the function of adrenal zona glomerulosa: studies in conscious rats.

The present experiments were designed to study the effect extracellular hyponatraemia on aldosterone secretion. Hyperaldosteronism was induced by peritoneal dialysis with 5% glucose solution in dexamethasone-pretreated rats. In the narrow physiological range of 135-142 mmol/l, as well as in the whole range of the study (122-142 mmol/l), the plasma concentration of sodium showed a close negative correlation with the serum concentration of aldosterone (r = -0.71 and -0.83, respectively). Plasma renin activity increased after peritoneal dialysis; however, no close correlation was observed either between sodium concentration and plasma renin activity or plasma renin activity and serum aldosterone concentration within the dialysed group. The ratio of serum concentration of aldosterone to plasma renin activity showed no considerable change between 132 and 142 mmol/l but rose steeply below 132 mmol sodium/l suggesting that a factor(s) other than angiotensin may also contribute to the induction of hyperaldosteronism.U