Adrenal cortical activity in sheep as measured by urinary 17-ketogenic steroid excretion

Abstract

The effects of a number of stimuli on adrenal activity in sheep were assessed from measurements of the output of urinary 17-ketogenic steroids (17-KGS). Evidence for the claim that 17-KGS excretion in sheep reflects adrenal cortical activity was provided by observations that injections of ACTH produced a marked rise in concentration of these steroid metabolites in the urine. A seasonal rhythm in the urinary excretion of 17-KGS was observed. The peak winter output of these steroids was eight times that found in midsummer. This pattern of adrenal activity appears to be temperature- and not light-induced. In the pregnant ewe, the urinary 17-KGS output followed normal seasonal fluctuations over the greater part of gestation. However, a sudden drop in values occurred during the 2 weeks prior to lambing. This was followed by a progressive rise post partum which was dependent on active lactation. The pre-partum fall in steroid excretion was also observed in pregnant ewes undergoing daily ACTH therapy. The significance of these findings is discussed. Pregnancy appears to modify the response of sheep to repeated intramuscular injections of ACTH. The steroid excretion rate was related to the dosage level of ACTH in both pregnant and non-pregnant ewes although gestation markedly reduced the total output. There was no evidence of adrenal atrophy with repeated cortisone injections over 8 weeks, but endogenous ACTH release appeared to be delayed when daily ACTH injections were discontinued. Injections of 300 mg cortisone acetate and 50 i.u. of ACTH, over a period, gave comparable excretion rates of 17-KGS in non-pregnant ewes.