Cyclic AMP indirectly mediates the extracellular Ca2+-independent release of LH.
This study was undertaken to determine whether cyclic AMP mediates the extracellular Ca2+-independent component of luteinizing hormone (LH) release. Gonadotropin releasing hormone (GnRH) increased cAMP production in female pituitaries incubated in Ca2+-free medium containing 3-isobutyl-1-methylxanthine (IBMX), but was ineffective in male pituitaries. The increases in female pituitaries were inhibited by flufenamate (flu). GnRH-stimulated LH secretion from male pituitaries was completely inhibited in Ca2+-free medium, whereas only a partial inhibition was obtained from female pituitaries, a response prevented by cycloheximide. Infusions of flu completely inhibited the extracellular Ca2+-independent release of LH, while dibutyryl cAMP (dbcAMP) partially restored this component of LH secretion. The dbcAMP-restored response was dependent upon protein synthesis. These results suggest that (i) the extracellular Ca2+-independent component of LH release is indirectly mediated by cAMP through the stimulation of de novo protein synthesis, and (ii) extracellular Ca2+ is required for the activation of adenylate cyclase in male but not in female gonadotrophs.
Bourne
G A
GA
Department of Physiology, University of Alberta, Edmonton, Canada.
D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D000242:Cyclic AMP / Q000494:pharmacology*; D005260:Female; D005439:Flufenamic Acid / Q000494:pharmacology; D007986:Luteinizing Hormone / Q000378:metabolism*; D008297:Male; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism; D010906:Pituitary Hormone-Releasing Hormones / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012737:Sex Factors
D010906:Pituitary Hormone-Releasing Hormones; D005439:Flufenamic Acid; D007986:Luteinizing Hormone; D000242:Cyclic AMP; D002118:Calcium