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Circulating human gamma-melanotropin precursor (76 amino acids) [N-POC(1-76) enhances the corticosterone and aldosterone response to corticotropin by isolated perfused rat adrenal cells [Al-Dujaili, Hope, Estivariz, Lowry & Edwards (1981) Nature (London) 291, 156-159]. Actinomycin D (4 x 10(-6) mol/litre) did not significantly affect corticotropin-induced corticosterone or aldosterone outputs, but completely inhibited the potentiating action of gamma-melanotropin precursor on rat adrenal cells. This suggests that the precursor enhances corticotropin-induced steroidogenesis via an increase in available mRNA produced from DNA transcription.

Two cystine-containing peptides isolated from human pituitaries were partially sequenced. The peptides are fragments derived from the amino-terminal of pro-opiocortin (NPOC) and have been chemically characterized as NPOC 1-28 (which lacks gamma-MSH) and NPOC 2-59. Their availability enables us to investigate new putative biological roles for the amino-terminal conserved sequence of pro-opiocortin.