Characterization of 12-O-tetradecanoyl-phorbol-13 acetate mediated ACTH release.
Activation of calcium-activated, phospholipid-dependent protein kinase C by phorbol esters such as 12-O-tetradecanoyl-phorbol-13-acetate (TPA) has been shown to mediate release of hormones in many systems. To investigate the role of protein kinase C in the mechanism of pituitary ACTH release, we studied the effect of the following conditions on TPA mediated ACTH release in primary rat pituitary cultures; corticotropin releasing hormone (CRH), different concentrations of extracellular calcium (Ca+2), nifedipine (a calcium channel blocker), PGE2 and cortisol (regulators of ACTH secretions). TPA induced ACTH release in a dose dependent fashion with an ED50 of 4.2 x 10(-10) M. The maximal amount of ACTH release individually induced by TPA (10(-8) M) and CRH (10(-8)) were identical. TPA (10(-8)) potentiated the amount of ACTH release from cells already maximally stimulated with CRH (4 x 10(-8) M). TPA mediated ACTH release was dependent on extracellular calcium and inhibited by nifedipine, to a maximum of 35%. Cortisol decreased the amount of ACTH individually released by TPA and CRH in a similar and dose dependent fashion with maximal inhibition of 47% occurring at 10(-7) M. PGE2 caused a dose dependent reduction of TPA mediated ACTH release. In conclusion, the pathways of ACTH release induced by CRH and TPA are not entirely the same but may share a common regulatory pathway. Extracellular calcium and calcium cell influx may be important for maximal ACTH release induced by TPA. Protein kinase C activation may play an important role in CRH stimulated ACTH release.
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Georgetown University Hospital, Department of Pediatrics, Washington, D.C. 20007.
D000324:Adrenocorticotropic Hormone / Q000097:blood*; D000818:Animals; D002478:Cells, Cultured; D003346:Corticotropin-Releasing Hormone / Q000494:pharmacology; D015232:Dinoprostone / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005260:Female; D006854:Hydrocortisone / Q000494:pharmacology; D009543:Nifedipine / Q000494:pharmacology; D010903:Pituitary Gland, Anterior / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
D000324:Adrenocorticotropic Hormone; D003346:Corticotropin-Releasing Hormone; D009543:Nifedipine; D015232:Dinoprostone; D013755:Tetradecanoylphorbol Acetate; D006854:Hydrocortisone