Differences in the Role of Cyclic Adenosine 3′,5′-Monophosphate during Capacitation of Bovine Sperm by Heparin or Oviduct Fluid1

Abstract

Capacitation is an important maturational event in the life of a spermatozoan that allows the sperm to undergo a stimulus-induced acrosome reaction. Bovine sperm can be induced to undergo capacitation in vitro by heparin or oviduct fluid, and capacitation can be inhibited by glucose. We found that glucose did not interfere with 3H-heparin binding to sperm. Glucose inhibition of capacitation could be reversed in a dose-dependent manner by 8-bromo-cAMP or by the phosphodiesterase inhibitors isobutylmethylxanthine or caffeine, with ED50S of 25, 32, and 183 microM, respectively. The maximal effect of 8-bromo-cAMP on capacitation was during the first 2 h of a 4-h incubation. Sperm cAMP increased during capacitation with heparin from an initial value of 4.1 +/- 0.1 to 7.3 +/- 1.1 pmol cAMP/20 x 10(6) sperm at 4 h of incubation. Control sperm cAMP at 4 h increased only to 4.9 +/- 0.8 pmol cAMP/20 x 10(6) sperm. There were both similarities and differences in the characteristics of capacitation by heparin or oviduct fluid. Both glucose and protamine sulfate were found to suppress the heparin-dependent cAMP increase and inhibit capacitation. Capacitation by oviduct fluid was inhibited by either glucose or protamine sulfate. A small increase in sperm cAMP was associated with capacitation by oviduct fluid but was not affected by glucose or protamine sulfate.