STIMULATION BY PROOPIOMELANOCORTIN-DERIVED PEPTIDES OF LH-RELEASE BY BULLFROG DISPERSED ANTERIOR-PITUITARY-CELLS

Labeling and immunoprecipitation experiments confirmed that three proo piomelanocortin (POMC)-derived peptides, the N-terminal peptide of POM C (NPP), joining peptide (JP) and adrenocorticotropic hormone (ACTH), were released by the bullfrog (Rana catesbeiana) anterior pituitary. T he effects of these three peptides on luteinizing hormone (LH) release by bullfrog dispersed anterior pituitary cells were studied. NPP and ACTH, but not JP, enhanced LH release concentration-dependently. Appro ximately 6 hr elapsed before the gonadotrophs responded to NPP and ACT H by releasing LH, whereas their response to human GnRH (hGnRH) was fa ster, suggesting that the modes of action of these two peptides and hG nRH differ. These results raise the possibility that NPP and ACTH act as paracrine factors in the bullfrog pituitary to enhance LH release e ither directly or indirectly.