RAPID NON-GENOMIC ACTIONS OF PROGESTERONE STIMULATE CA2+ INFLUX AND THE ACROSOME REACTION IN HUMAN SPERM

This review summarizes some recent findings in human sperm which show that progesterone and 17alpha hydroxyprogesterone are able rapidly (wi thin seconds) to elevate [Ca2+]i and elicit the acrosome reaction (AR) via a non-genomic cell surface receptor. Progesterone promotes a tran sient elevation in [Ca2+]i which is blocked by extracellular La3+ and Ni2+ and removal of extracellular Ca2+ following chelation with EGTA. Some studies suggest that polyamines, trypsin-like proteases, and prog esterone receptor aggregation are involved in progesterone-induced Ca2 + influx and AR. The receptor is not stimulated by the potent syntheti c progestigins (e.g. promegestone, norethynodrel, megestrol acetate, c yproterone acetate) and is weakly antagonized by the genomic anti-prog estins RU 486 and ZK 98.299. The sedative-hypnotic 3alpha hydroxyl A-r ing reduced pregnane steroids, which are powerful activators of the GA BA(A) Cl- channel, are weak activators of Ca2+ influx and the AR. Thes e data suggest that human sperm have a cell surface steroid receptor w hich is unlike the genomic progesterone receptor and the GABA(A) Cl- c hannel steroid receptor.