title: Extragenomic actions of progesterone in human sperm and progesterone metabolites in human platelets.
abstract: Progesterone rapidly increased intracellular free calcium ([Ca2+]i) in human sperm, removal of extracellular Ca2+ prevented the increase in [Ca2+]i. The Ca2+ influx was not blocked by the T-type Ca2+ channel blocker mibefradil. However T-type calcium channels do appear to be present in human sperm because the neoglycoprotein mannose-albumin, an inducer of the acrosome reaction, was able to promote Ca2+ influx, which was blocked by mibefradil and more potently inhibited by Ni2+ than Cd2+. The receptor for progesterone that promotes the Ca2+ influx was located on the plasma membrane using FITC-progesterone-albumin. It is concluded that progesterone stimulates Ca2+ influx in human sperm via a unique Ca2+ channel possibly similar to a store-operated channel (SOC) or a receptor-operated channel (ROC). We have found that progesterone metabolites, such as pregnanolone and pregnanediol, promote a rapid rise in [Ca2+]i and aggregation in human platelets, similar to that observed with thrombin. The increase in [Ca2+]i was prevented when extracellular Ca2+ was removed or by the SOC inhibitor SKF-96365. The phospholipase C inhibitor U-73122 also prevented the increase in [Ca2+]i, suggesting that these metabolites interact with a cell surface receptor on the platelet to activate phospholipase C to produce inositol-P3, which mobilizes intracellular Ca2+, thereby activating the SOC in the plasma membrane. Progesterone and estradiol conjugated to albumin, also produced a rapid increase in [Ca2+]i, which was prevented by Ca2+ removal from the medium or when SKF-96365 or U-73122 were added. It is proposed that human platelets possess cell surface receptors for steroids.
mesh_terms: D001792:Blood Platelets / Q000378:metabolism*; D002118:Calcium / Q000097:blood; D015220:Calcium Channels / Q000378:metabolism; D004967:Estrogens / Q000378:metabolism; D006801:Humans; D008297:Male; D011374:Progesterone / Q000378:metabolism / Q000502:physiology*; D011376:Progesterone-Binding Globulin / Q000378:metabolism; D011485:Protein Binding; D012709:Serum Albumin / Q000378:metabolism; D013094:Spermatozoa / Q000502:physiology*