The fate of ACTH released from rat anterior pituitary into the incubation medium in vitro: enzymatic degradation and acid activation.

The bioactivity of ACTH released from isolated rat anterior pituitary glands into the incubation medium was determined. After the pituitaries were removed, ACTH activity in the medium decreased exponentially during further incubation at 37degreesC. The loss of ACTH activity was temperature- and pH-dependent and inhibited both by protease inhibitor (trasylol) and by preheating. Crude tissue extracts from median eminence, cerebral cortex and liver similarly inhibited the loss of ACTH activity. These results indicate that ACTH released into the medium may be destroyed by proteolytic enzyme(s) from the rat anterior pituitary. ACTH activity in the incubation medium was increased promptly by acidification of the medium to pH 1.5-2.5 with HC1, and reduced to the initial level by NaOH reneutralization of the medium (pH 6.8-7.8). These phenomena were not observed after the incubation medium had been heated at 100degreesC for 5 min.