In vitro and in vivo adrenal corticosteroid secretion following stress

Abstract

Sprague-Dawley rats were ssressed by scalding or by physical immobilization. Several aspects of the pituitary-adrenal response after these stresses were examined by: a) in vivo adrenal vein cannulation with chromatographic identification and estimation of the rate of secretion of corticosterone; b) measurement of the in vitro steroidogenesis by adrenal gland slices; c) determination of adrenal ascorbic acid concentration, and d) determination of the pituitary ACTH content. After the stresses of either scalding or physical immobilization, there was an initial biphasic response consisting of a brief elevated secretion of hormone followed by a period of lower or less than normal output. After this initial response, the expected high, sustained rate of hormone secretion was observed. The low level of hormone secretion during this initial biphasic response was not due to secretory exhaustion of the adrenal, and the pituitary contained approximately a twice-normal concentration of ACTH. The low level of hormone secretion was replaced by very high levels by treatment of the stressed rat with reserpine or by placement of hypothalamic lesions. At a variable time after stress, corresponding to time of least corticosteroid secretion, there appears to exist an inability of the pituitary to release ACTH, which may be due to cessation of the initial hypothalamic stimulation or to a neural mechanism which temporarily suppresses or inhibits the secretion of endogenous ACTH.