Effects of polyamine biosynthesis inhibitors on the progesterone-initiated increase in intracellular free Ca2+ and acrosome reactions in human sperm.

This laboratory has previously reported that progesterone can initiate a rapid transient increase in the concentration of intracellular free Ca2+ ([Ca2+]i) and an increase in a Ca(2+)-requiring exocytotic event, the acrosome reaction (AR) in human sperm. Rapid increases in Ca2+ fluxes of some mammalian cells caused by another steroid, testosterone, require polyamine biosynthesis. Herein, we tested two polyamine biosynthesis suicide inhibitors for their effects on the progesterone-initiated increase in [Ca2+]i and AR in capacitated human sperm in vitro: DL-alpha-(difluoromethyl)ornithine hydrochloride (DFMO), an inhibitor of putrescine synthesis by ornithine decarboxylase and (5'[[(Z)-4-amino-2-butenyl]methylamino]-5'-deoxyadenosine (MDL 73811), an inhibitor of S-adenosylmethionine decarboxylase (required for spermidine and spermine synthesis). Sperm were capacitated in vitro and preincubated 10 min with 4.9 mM DFMO or 9.8 microM MDL 73811 with or without various polyamines (245 microM). Progesterone (3.09 microM final concentration) or progesterone solvent (ethanol, 0.1% final concentration) was then added, sperm fixed 1 min after additions and AR assayed by indirect immunofluorescence or with fluorescein-labeled Con A lectin. DFMO strongly inhibited the AR, but putrescine (product of ornithine decarboxylase and precursor of spermidine and spermine) reversed that inhibition. Preincubation for 25 min with DMFO + spermidine also reversed DFMO inhibition. MDL 73811 inhibited the progesterone-initiated AR, and a 10 min preincubation with spermidine, but not putrescine or spermine, reversed that inhibition. Preincubations with putrescine alone or with spermidine alone followed by addition of the progesterone solvent did not initiate the AR, and such preincubations followed by progesterone addition did not increase the AR more than progesterone alone.(ABSTRACT TRUNCATED AT 250 WORDS)