Corticosteroid response of rabbits and rats to exogenous ACTH

The dynamics of the alterations of the cortisol: corticosterone ratio in rabbits during porcine ACTH administration were studied on an almost daily basis and as a function of time after injection. In rabbits the cortisol: corticosterone ratio increased strikingly but variably during the treatment period. Rats responded to similar treatment only with increased corticosterone release. The differences are attributed to the presence of 1-39 ACTH as well as intermediate ACTH in the rabbit pituitary but not in the rat pituitary.