Ca2(+)-independent secretory mechanism of thyrotropin-releasing hormone (TRH) involves protein kinase C in rat pituitary cells.
Thyrotropin-releasing hormone (TRH) stimulates biphasic prolactin (PRL) secretion from rat pituitary GH3 cells. The pretreatment of cells with EGTA (100 microM) plus arachidonic acid (15 microM), a condition which decreased TRH-responsive intracellular Ca2+ pools, eliminated the activity of TRH on burst PRL secretion (2 min) but did not alter that on sustained PRL secretion (30 min). However, the treatment of cells with EGTA, arachidonic acid and H-7 (300 microM), a potent inhibitor of protein kinase C (PKC), almost completely suppressed the activity of TRH for sustained PRL secretion. In cells down-modulated for PKC, TRH abolished this Ca2(+)-independent sustained PRL secretion. These results suggest that TRH acts through a separate, Ca2(+)-independent secretory mechanism, besides by modulating the Ca2(+)-dependent mechanism and that PKC is involved in this Ca2(+)-independent secretory pathway.
Yajima
Y
Y
Department of Tumor Cell Biology, Tokyo Metropolitan Institute of Medical Science, Japan.
Akita
Y
Y
Yamaguchi
A
A
Saito
T
T
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D003593:Cytoplasm / Q000187:drug effects / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004533:Egtazic Acid / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D010902:Pituitary Gland / Q000187:drug effects / Q000201:enzymology*; D011388:Prolactin / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D013973:Thyrotropin-Releasing Hormone / Q000008:administration & dosage / Q000494:pharmacology*
D004533:Egtazic Acid; D013973:Thyrotropin-Releasing Hormone; D011388:Prolactin; D011493:Protein Kinase C; D002118:Calcium