Effect of Temporary Thoracic Caval Constriction on Aldosterone Secretion in Conscious and in Anesthetized Sheep

Abstract

Temporary constriction of the thoracic inferior vena cava of conscious Nareplete sheep was produced by inflation of a Teflon-enclosed rubber cuff. Moderate constriction caused a decrease in the parotid salivary Na/K ratio equivalent to the effect of intravenous infusion of 5–10 μg/hr of Daldosterone. Moderate constriction caused little change in the sheep’s demeanor, cardiac and respiratory rate and blood pressure. Severe constriction produced large effects on these variables and a larger parotid response. The time course of the parotid response indicated rapid increase and decrease of the aldosterone secretion rate with inflation and deflation of the cuff. Infusion of Aldactone at 40 mg/hr blocked the parotid response to moderate caval constriction. Intravenous infusions of mixtures of cortisol and corticosterone at rates approximating maximal adrenal output under ACTH stimulation (5.5 mg/hr and 275 μg/hr. respectively) failed to reproduce the parotid response to thoracic caval constriction. Under anesthesia, caval constriction caused the secretion rate of aldosterone in adrenal vein plasma to increase from 2.4 μg/hr to 8.2 μg/hr with no change in the already elevated cortisol output. It is concluded that moderate caval constriction in conscious sheep caused an increase in the aldosterone secretion rate.