THE SPECIFIC ACTIVITY OF PLASMA CORTISOL IN SHEEP DURING CONTINUOUS INFUSION OF [1,2-3H2]CORTISOL, AND ITS RELATION TO THE RATE OF CORTISOL SECRETION

Abstract

SUMMARY: Tritium-labelled cortisol was infused intravenously for about 4 hr. into sheep with autotransplanted left adrenal glands. The specific activity of plasma cortisol became constant about 2 hr. after beginning the infusion, and in almost all experiments, the rate of cortisol secretion and the concentration of cortisol in plasma were constant during the remainder of the period of infusion. The rate of cortisol turnover was calculated as the ratio of the rate of infusion of labelled cortisol and the constant specific activity which was attained during infusion. Within the limits of experimental error, the calculated rate of cortisol turnover in 55 experiments was equal to the simultaneously measured rate of cortisol secretion. In sheep which were accustomed to handling, the rate of cortisol secretion was about 12 μg./min. and the concentration of cortisol in plasma was about 18 μg./l. The rate of cortisol secretion did not change during pregnancy in ewes, but there was a decrease in the concentration of cortisol in plasma in the last 2 weeks before lambing.