A serine-proteinase inhibitor (Boc-D-Phe-Pro-Arg-H) inhibits the secretion of adrenocorticotropin- and beta-endorphin-immunoreactive peptides in vitro.

The effects of a potent serine protease inhibitor, Boc-D-Phe-Pro-Arg-H, on the secretion and content of ACTH and beta-endorphin-like immunoreactivities of cultured rat anterior pituitary cells were studied. Basal release of the hormones was not affected by the drug but secretion in response to stalk-median eminence extracts was inhibited. The inhibitor did not effect the amount of ACTH or beta-endorphin in the medium plus the cells, nor did it change the ratio of the lipotropin and beta-endorphin-like immunoreactivities. Thus the compound seems to affect the release of ACTH and beta-endorphin, but not the processing of lipotropin to beta-endorphin.