The role of calcium in luteinizing hormone/human chorionic gonadotrophin stimulation of Leydig cell immunoactive inhibin secretion in vitro.
The mechanism by which luteinizing hormone (LH) stimulates Leydig cell immunoactive inhibin (I-inhibin) secretion was investigated using Percoll-purified adult rat Leydig cells. Using a maximally stimulating dose of LH (16 ng/ml). Leydig cell I-inhibin secretion was non-detectable at 1-2 h of incubation, but subsequently increased at all time points during a 25 h incubation period. LH stimulated both Leydig cell content and release of I-inhibin. Increasing concentrations of LH stimulated both inhibin and testosterone immunoactivity in the incubation media over a similar dose-response range, with a 2- to 4-fold rise in I-inhibin secretion at maximal doses of LH. Dibutyryl cAMP stimulated testosterone secretion in a manner similar to that of LH, but I-inhibin secretion was less sensitive than testosterone and a significant stimulation was observed only at the highest doses (200-1000 micrograms/ml). LH-stimulated I-inhibin secretion was significantly decreased when Leydig cells were incubated in calcium-depleted (0.15 mM Ca2+ + 1 mM EGTA) or low [Ca2+] media (0.15 mM) as compared to normal (1.15 mM) or high [Ca2+] (2-5 mM) media. In contrast, LH-stimulated testosterone secretion remained unchanged by altering extracellular [Ca2+], and although decreased in the presence of EGTA, testosterone secretion remained significantly greater than basal levels. Furthermore both diltiazem and verapamil completely blocked the LH and dibutyryl cAMP-stimulated increase in Leydig cell I-inhibin, but did not reduce either LH or dibutyryl cAMP-stimulated testosterone production to basal levels. We conclude that LH stimulates both I-inhibin synthesis and release by adult rat Leydig cells in culture, by mechanisms involving calcium.
Simpson
B J
BJ
Department of Anatomy, Monash University, Melbourne, Victoria, Australia.
Risbridger
G P
GP
Hedger
M P
MP
de Kretser
D M
DM
D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002478:Cells, Cultured; D006063:Chorionic Gonadotropin / Q000494:pharmacology*; D000242:Cyclic AMP / Q000502:physiology; D007265:Inhibins / Q000378:metabolism*; D007985:Leydig Cells / Q000187:drug effects / Q000378:metabolism*; D007986:Luteinizing Hormone / Q000494:pharmacology*; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D011994:Recombinant Proteins / Q000494:pharmacology; D015290:Second Messenger Systems; D012636:Secretory Rate / Q000187:drug effects; D013268:Stimulation, Chemical; D013739:Testosterone / Q000378:metabolism
D002121:Calcium Channel Blockers; D006063:Chorionic Gonadotropin; D011994:Recombinant Proteins; D013739:Testosterone; D007265:Inhibins; D003994:Bucladesine; D007986:Luteinizing Hormone; D000242:Cyclic AMP; D002118:Calcium