Influence of neurohypophysectomy on the renal actions of aldosterone in the adrenalectomized rat.

The influence of aldosterone administration on urine flow, Na+ and K+ excretion was examined in hypotonic saline infused, Inactin anesthetised rats following removal of the adrenals or adrenals and posterior pituitary. Plasma adrenal steroid levels were considerably depressed but still detectable 10-14 days after adrenalectomy. Removal of the posterior pituitary markedly reduced Na+ excretion in adrenalectomized animals implying that Na+ retention following neurohypophysectomy is not dependent on adrenal gland function. In adrenalectomized rats aldosterone administration at 42 pmol/min reduced Na+ excretion and urine flow without significantly changing K+ excretion, though plasma K+ was reduced. In adrenalectomized/neurohypophysectomized rats aldosterone further reduced the already low rate of Na+ excretion and increased K+ excretion, though there was no observable effect on urine flow. The results obtained indicate that the Na(+)-retaining actions of aldosterone are largely independent of posterior pituitary influence. The K(+)-losing action of aldosterone was, however, only observed in animals in which the posterior pituitary was absent.