Progesterone metabolites rapidly stimulate calcium influx in human platelets by a src-dependent pathway.
The effects of several steroids and their metabolites were examined for their ability to rapidly alter intracellular free calcium ([Ca(2+)](i)) in the anucleate human platelet. Earlier studies suggested that steroids had direct and rapid non-genomic effects to alter platelet physiology. The rationale for performing this study was to investigate the signal transduction events being activated by steroids. Super-physiologic concentrations (1.0-10.0microM) of beta-estradiol and several estradiol metabolites and analogs potentiated (approximately twofold) the action of thrombin to elevate [Ca(2+)](i) in platelets, whereas 10.0microM progesterone inhibited the action of thrombin by 10-15%. Progesterone and beta-estradiol by themselves did not affect [Ca(2+)](i). Progesterone metabolites can achieve high blood concentrations. Some progesterone metabolites, particularly those in the beta-conformation, were potent stimulators of Ca(2+) influx and intracellular Ca(2+) mobilization in platelets. They activated phospholipase C because their ability to increase [Ca(2+)](i) was inhibited by the phospholipase C inhibitor U-73122. The ability of pregnanediol and collagen to increase [Ca(2+)](i) was inhibited by the src tyrosine kinase inhibitor PP1, whereas the actions of thrombin and thapsigargin to increase [Ca(2+)](i) were not affected by PP1. The effects of progesterone metabolites to increase [Ca(2+)](i) were observed with concentrations as low as 0.1microM. Pregnanolone synergized with thrombin to increase [Ca(2+)](i). It is hypothesized that human platelets possess receptors for progesterone metabolites. These receptors when stimulated will activate platelets by causing a rapid increase in [Ca(2+)](i). Pregnanolone, isopregnanediol and pregnanediol were the most effective stimulators of this newly identified src-dependent signal transduction system in platelets. Progesterone metabolites may regulate platelet aggregation and hence thrombosis in vivo.
Blackmore
Peter F
PF
Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, VA 23501-1980, USA. blackmPF@evms.edu
D001792:Blood Platelets / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D003094:Collagen / Q000378:metabolism; D004958:Estradiol / Q000378:metabolism* / Q000494:pharmacology; D006801:Humans; D011276:Pregnanediol / Q000378:metabolism; D011374:Progesterone / Q000378:metabolism* / Q000494:pharmacology; D015398:Signal Transduction; D013256:Steroids / Q000494:pharmacology; D013917:Thrombin / Q000378:metabolism*; D010738:Type C Phospholipases / Q000378:metabolism; D019061:src-Family Kinases / Q000378:metabolism
D013256:Steroids; D011374:Progesterone; D004958:Estradiol; D003094:Collagen; D019061:src-Family Kinases; D010738:Type C Phospholipases; D013917:Thrombin; D011276:Pregnanediol; D002118:Calcium