title: PMA-sensitive protein kinase C is not necessary in TRH-stimulated prolactin release from female rat primary pituitary cells.
abstract: In GH3 cells and other clonal rat pituitary tumor cells, TRH has been shown to mediate its effects on prolactin release via a rise of cytosolic Ca2+ and activation of protein kinase C. In this study, we examined the role of protein kinase C in TRH-stimulated prolactin release from female rat primary pituitary cell culture. Both TRH and PMA stimulated prolactin release in a dose-dependent manner. When present together at maximal concentrations, TRH and PMA produced an effect which was slightly less than additive. Pretreatment of rat pituitary cells with 10(-6) M PMA for 24 hrs completely down-regulated protein kinase C, since such PMA-pretreated cells did not release prolactin in response to a second dose of PMA. Interestingly, protein kinase C down-regulation had no effect on TRH-induced prolactin release from rat pituitary cells. In contrast, PMA-pretreated GH3 cells did not respond to a subsequent stimulation by either PMA or TRH. Pretreatment of rat pituitary cells with TRH (10(-7) M, 24 hrs) inhibited the subsequent response to TRH, but not PMA. Forskolin, an adenylate cyclase activator, stimulated prolactin release by itself and in a synergistic manner when incubated together with TRH or PMA. The synergistic effects of forskolin on prolactin release was greater in the presence of PMA than TRH. Down-regulation of protein kinase C by PMA pretreatment abolished the synergistic effect produced by PMA and forskolin but had no effect on those generated by TRH and forskolin. sn-1,2-Dioctanylglycerol (DOG) pretreatment attenuated the subsequent response to DOG and PMA but not TRH. The effect of TRH, but not PMA, on prolactin release required the presence of extracellular Ca2+. In conclusion, the mechanism by which TRH causes prolactin release from rat primary pituitary cells is different from that of GH3 cells; the former is a protein kinase C-independent process whereas the latter is at least partially dependent upon the activation of protein kinase C.
authors.affiliation: Department of Growth Biochemistry and Physiology, Merck Research Laboratories, Rahway, NJ 07065.
authors.forename: K
authors.initials: K
authors.lastname: Cheng
authors.forename: W W
authors.initials: WW
authors.lastname: Chan
authors.forename: R
authors.initials: R
authors.lastname: Arias
authors.forename: A
authors.initials: A
authors.lastname: Barreto
authors.forename: B
authors.initials: B
authors.lastname: Butler
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D004075:Diglycerides / Q000494:pharmacology; D015536:Down-Regulation / Q000187:drug effects; D004789:Enzyme Activation; D005260:Female; D010903:Pituitary Gland, Anterior / Q000187:drug effects* / Q000378:metabolism; D011388:Prolactin / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism*; D011863:Radioimmunoassay; D051381:Rats; D017208:Rats, Wistar; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
chemical_list: D004075:Diglycerides; C044295:1,2-dioctanoylglycerol; D005576:Colforsin; D013973:Thyrotropin-Releasing Hormone; D011388:Prolactin; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium