Effect of serum proteinase inhibitors on the fertilizing capacity of rabbit spermatozoa.

The in vivo effect of purified human alpha1-antitrypsin and inter-alpha-trypsin inhibitor on the fertilizing ability of capacitated rabbit spermatozoa was investigated and compared with that of the trypsin-kallikrein inhibitor from bovine organs (Trasylol). Only 250 mug of alpha1-antitrypsin/5 X 10(4) sperm in 0.05 ml inhibited fertilization by more than 50%. Lower concentrations of alpha1-antitrypsin (50 mug/5 X 10(4) sperm in 0.05 mo) and inter-alpha-trypsin inhibitor in amounts of 250 mug/5 X 10(4) sperm and less had no significant effect on the fertilization rate. Comparative experiments with Trasylol in conentrations of 50 mug/5 X 10(4) sperm resulted in more than 50% fertilization inhibition, whereas 100 mug/5 X 10(4) sperm decreased the fertilization rate by approximately 90%. The differences in the antifertility effect of these acrosin inhibitors toward capacitated spermatozoa may be due to differences in molecular weight. The effective concentrations required for fertilization inhibition appear to be relatively high under the experimental conditions used.