Failure of ACTH to mimic the stress-induced activation of rat adrenocortical cholesterol ester hydrolase in vivo

Rat adrenocortical cholesterol ester hydrolase activity does not respond to the circadian rhythm of the pituitary-adrenal axis under quiescent conditions. However, stress activates this enzyme, producing a greater increase in activity at the high point of the cycle than at the low point. This stress-induced effect requires the presence of the pituitary. It is not mimicked by administration of exogenous porcine ACTH to either hypophysectomized or dexamethasone-suppressed rats, but homogenates of whole rat pituitary tissue do possess substantial stimulatory capacity.