ACTH-Induced protein release from the perfused cat adrenal gland: Evidence for exocytosis?

The relationship between the release of protein and hormone secretion from the isolated perfused cat adrenal gland was investigated. ACTH increased the rate of protein release in a manner which was temporally related to steroid secretion. The enhanced protein secretion-like steroid release-was blocked by calcium deprivation; but cycloheximide, which inhibits ACTH-induced steroid release, failed to block the enhanced protein release. Stimulation of the medulla by acetylcholine or nicotine also increased the protein concentration of the perfusate, but the increase after medullary stimulation was less relative to augmented hormone release than after cortical stimulation. Polyacrylamide gel electrophoresis of samples of SDStreated adrenal perfusates showed the presence of two distinct bands; the molecular weights of these two proteins were determined to be 12, 500 and 70, 000. These bands were more prominent in the perfusate after exposure to ACTH, suggesting that they represent specific protein or protein subunits whose release is induced by ACTH. Although the source of the released protein remains to be elucidated, the results are consistent with the concept that the events associated with corticosteroid release involve a process identical with-or related to-exocytosis.