Estradiol modulation of PMA--and ionomycin-stimulated LH secretion from pituitaries of castrated rats.
Quartered pituitaries from castrated (72 h) +/- estradiol (E2)-treated (24 h) rats were used in a perifusion system to investigate estradiol modulation of ionomycin and ionomycin + PMA stimulated LH secretion. Estradiol enhanced the LH responses to GnRH (1 nM) and ionomycin (10 microM), and was necessary for the manifestation of PMA-stimulated (1 microM) LH secretion. Cycloheximide (5 microM) inhibited the E2-enhanced responses to GnRH, ionomycin and PMA. The protein synthesis inhibitor also partially suppressed the GnRH response from pituitaries of castrates, but was totally ineffective against the ionomycin-induced LH secretion. Protein synthesis-dependent, synergistic interactions between PMA and ionomycin were evident from pituitaries of castrates (even though PMA alone was an ineffective secretagogue). Synergistic interactions were not apparent from pituitaries of castrated + E2-treated rats. These results indicate that: (i) estradiol enhances the responsiveness of male gonadotropes to ionomycin and PMA by protein synthesis-dependent mechanisms which appear to mask their synergistic interactions; and (ii) increases in cytoplasmic Ca2+ might be a prerequisite for an expression of the involvement of PKC as a mediator of LH secretion in the absence of high concentrations of estradiol.
Fahmy
N W
NW
Department of Physiology, University of Saskatchewan, Saskatoon, Canada.
Bourne
G A
GA
D000818:Animals; D003513:Cycloheximide / Q000494:pharmacology; D004347:Drug Interactions; D004958:Estradiol / Q000494:pharmacology*; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D015759:Ionomycin / Q000494:pharmacology*; D007986:Luteinizing Hormone / Q000378:metabolism*; D008297:Male; D009919:Orchiectomy; D010903:Pituitary Gland, Anterior / Q000187:drug effects* / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012636:Secretory Rate / Q000187:drug effects; D013268:Stimulation, Chemical; D013737:Testis / Q000502:physiology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
D007987:Gonadotropin-Releasing Hormone; D004958:Estradiol; D015759:Ionomycin; D007986:Luteinizing Hormone; D003513:Cycloheximide; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate