Mechanisms of release of prolactin from fowl anterior pituitary glands incubated in vitro: effects of calcium and cyclic adenosine monophosphate.
Fowl anterior pituitary glands were bisected and each half was pretreated in either Medium 199 or medium containing EGTA to deplete endogenous calcium (Ca2+) stores, after which they were incubated in Medium 199, or Ca2+-free medium, containing prolactin release-stimulating agents and verapamil, a Ca2+ channel blocker. High K+ concentrations, hypothalamic extract, synthetic thyrotrophin-releasing hormone (TRH) and dibutyryl cyclic AMP (dbcAMP) all stimulated release of prolactin from control (non EGTA-treated) hemianterior pituitary glands. The effects of TRH and dbcAMP were not additive, but the response to submaximal concentrations of TRH was augmented by theophylline, a phosphodiesterase inhibitor. Reduction of Ca2+ availability with EGTA or verapamil reduced basal release of prolactin, prevented the prolactin-stimulating effects of high K+ concentrations and TRH, and markedly attenuated responses to hypothalamic extract and dbcAMP, EGTA being more effective than verapamil. Increasing the Ca2+ concentration of the medium did not augment basal or stimulated release of prolactin. These results suggest that both Ca2+ and cyclic AMP may act as intracellular mediators in the release of prolactin. Both basal and stimulated release of prolactin depend upon the presence of Ca2+. Although influx from the medium may be the major source of Ca2+, endogenous stores of Ca2+, perhaps mobilized by dbcAMP, may be able to maintain some release of prolactin. The prolactin-stimulating effects of TRH may be mediated by cyclic AMP.
Hall
T R
TR
Harvey
S
S
Chadwick
A
A
D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D002118:Calcium / Q000172:deficiency*; D002645:Chickens; D000242:Cyclic AMP / Q000494:pharmacology*; D004533:Egtazic Acid / Q000494:pharmacology; D066298:In Vitro Techniques; D010903:Pituitary Gland, Anterior / Q000187:drug effects / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D011388:Prolactin / Q000378:metabolism*; D013806:Theophylline / Q000494:pharmacology; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology
D004533:Egtazic Acid; D013973:Thyrotropin-Releasing Hormone; D003994:Bucladesine; D011388:Prolactin; D013806:Theophylline; D014700:Verapamil; D000242:Cyclic AMP; D011188:Potassium; D002118:Calcium