STUDIES RELATED TO PROGESTERONE-INDUCED HAMSTER SPERM ACROSOME REACTION

Experiments were designed to characterize the effect of progesterone o n the hamster sperm acrosome reaction (AR). Progesterone stimulated ex ocytosis of previously capacitated spermatozoa in a dose-dependent man ner. Progesterone-3-(O-carboxymethyl)oxime:BSA conjugate also induced AR when added to capacitated sperm suspensions. EGTA and La3+, added 1 0 min before progesterone, completely abolished the steroid-stimulator y effect. Benzamidine, a trypsin inhibitor, also inhibited AR when add ed to sperm cells 10 min before progesterone. This effect was avoided when spermatozoa were treated with the Ca2+ ionophore ionomycin. Conve rsely, the H+ ionophore FCCP, or the Na+/K+ ionophore nigericin, did n ot prevent the effect of the inhibitor. Results suggest that progester one acts on the hamster sperm plasma membrane to stimulate exocytosis, which requires external Ca2+ and presumably Ca2+ influx. In addition, a sperm trypsin-like protease may be part of the mechanism by which p rogesterone stimulates AR. Since the ionomycin-induced AR does not req uire this proteolytic activity, the possible involvement of such an en zyme in the progesterone-stimulated Ca2+ influx necessary for the occu rrence of AR is discussed. (C) 1996 Wiley-Liss, Inc.