Biphasic activation of cytosolic free calcium and LH responses by gonadotropin-releasing hormone.
Gonadotropin-releasing hormone (GnRH) stimulates rapid peak increases in [Ca2+]i and LH release, followed by lower but sustained elevations of both [Ca2+]i and hormone secretion. Omission of extracellular Ca2+ only slightly decreased the peak of [Ca2+]i, but reduced the peak LH response by 40% and prevented the prolonged increases in [Ca2+]i and LH release. Dihydropyridine calcium antagonists did not affect the peak [Ca2+]i and LH responses, but reduced the sustained increases by up to 50%. Whereas GnRH-induced mobilization of intracellular calcium initiates the LH peak, and Ca2+ entry through dihydropyridine-insensitive channels contributes to the peak and plateau phases of LH release, dihydropyridine-sensitive L-type Ca2+ channels participate only in the sustained phase of gonadotropin secretion.
Tasaka
K
K
Endocrinology and Reproduction Research Branch, National Institute of Child Health and Human Development, Bethesda, MD 20892.
Stojilkovic
S S
SS
Izumi
S
S
Catt
K J
KJ
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D066298:In Vitro Techniques; D007700:Kinetics; D007986:Luteinizing Hormone / Q000378:metabolism*; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains
D007987:Gonadotropin-Releasing Hormone; D007986:Luteinizing Hormone; D002118:Calcium