The role of Ca2+ in steroidogenesis in Leydig cells. Stimulation of intracellular free Ca2+ by lutropin (LH), luliberin (LHRH) agonist and cyclic AMP.
The requirements of purified rat Leydig cells for intra- and extra-cellular Ca2+ during steroidogenesis stimulated by LH (lutropin), cyclic AMP analogues and LHRH (luliberin) agonist were investigated. The intracellular Ca2+ concentrations ([Ca2+]i) were measured by using the fluorescent Ca2+ chelator quin-2. The basal [Ca2+]i was found to be 89.4 +/- 16.6 nM (mean +/- S.D., n = 25). LH, 8-bromo cyclic AMP and dibutyryl cyclic AMP increased [Ca2+]i, by 300-500 nM at the highest concentrations of each stimulator, whereas LHRH agonist only increased [Ca2+]i by a maximum of approx. 60 nM. Low concentrations of LH (less than 1 pg/ml) and all concentrations of LHRH agonist increased testosterone without detectable changes in cyclic AMP. With amounts of LH greater than 1 pg/ml, parallel increases in cyclic AMP and [Ca2+]i occurred. The steroidogenic effect of the LHRH agonist was highly dependent on extracellular Ca2+ concentration ([Ca2+]e), whereas LH effects were only decreased by 35% when [Ca2+]e was lowered from 2.5 nM to 1.1 microM. No increase in [Ca2+]i occurred with the LHRH agonist in the low-[Ca2+]e medium, whereas LH (100 ng/ml) gave an increase of 52 nM. It is concluded that [Ca2+]i can be modulated in rat Leydig cells by LH via mechanisms that are both independent of and dependent on cyclic AMP, whereas LHRH-agonist action on [Ca2+]i is independent of cyclic AMP. The evidence obtained suggests that, at sub-maximal rates of testosterone production, Ca2+, rather than cyclic AMP, is the second messenger, whereas for maximum steroidogenesis both Ca2+- and cyclic-AMP-dependent pathways may be involved.
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D000242:Cyclic AMP / Q000096:biosynthesis / Q000494:pharmacology*; D005110:Extracellular Space / Q000378:metabolism; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D066298:In Vitro Techniques; D007985:Leydig Cells / Q000187:drug effects / Q000378:metabolism*; D007986:Luteinizing Hormone / Q000494:pharmacology*; D008297:Male; D051381:Rats; D013050:Spectrometry, Fluorescence; D013739:Testosterone / Q000096:biosynthesis*
D007987:Gonadotropin-Releasing Hormone; D013739:Testosterone; D007986:Luteinizing Hormone; D000242:Cyclic AMP; D002118:Calcium