Factors affecting the antidiuretic actions of the 18-monoacetate of (+)-aldosterone and of a substance secreted by eart muscle, in rats.

Abstract

Abstract The method for the assay of a steroid-like substance secreted by the heart (HS) in terms of the biological activity of the 18-monoacetate of (+)-aldosterone (18MA) has been improved. Rats were equipped with ascending carotid, descending external jugular and bladder polyethylene cannulae and the urethra was ligated, under pentobarbitone anaesthesia, 24–36 h before use. Assays were made in restrained animals during sustained water diuresis induced by an intravenous infusion of glucose, 5%, and NaCl, 0ṁ9%; 2: 1 at 9 mlh−1. Antidiuretic responses (measured as the area under the curve) to ascending carotid injections of 18MA and of HS, made at 0ṁ01 ml s−1, maximum 15 s, were obtained from single dilutions of HS and 18MA: urine flow per min was recorded from drop (0ṁ025 ml) counters. Denervation of the carotid sinus above the carotid cannula did not influence the antidiureses. Data obtained were analysed by normal statistical procedures. Ascending carotid injections of 18MA and HS did not influence mean systemic arterial pressures, the clearances of creatinine and of PAH or the urinary outputs of Na+ and K+. The antidiuresis produced was compatible with the release of ADH by HS and by 18MA. Marked seasonal variations in threshold sensitivity to 18MA and in the slopes of the log dose-effect curves for the antidiuretic actions of 18MA are described. Variations both in the threshold sensitivity and in the log dose-effect curves for the anti-diuresis caused by 18MA occur between rats of different strains.