Relationship between heparin binding to spermatozoa and the fertility of dairy bulls

The presence of heparin in in vitro media has been implicated in improved f ertility parameters of bull spermatozoa. In a previous study, Zhang et al. (25) obtained an estimate of bull nonreturn rates based on spermatozoal con centration, motility and zona pellucida binding (24). The objective of this study was to test for a relationship between fertility parameters previous ly estimated for the same batch of cryopreserved semen (25) and amount of h eparin bound to spermatozoa. H-3-heparin binding to spermatozoa was assesse d by radioimmunoassay, and statistical correlations were drawn to previousl y measured sperm characteristics. Preliminary experiments established optim al binding conditions of 25 degreesC, and 60 min incubation with H-3-hepari n at a concentration of 50,000 cpm. H-3-heparin bound to an average of 2.2 x 10(6) receptors/ cell with a K-d of 2.0 x 10(-7) M. The total H-3-heparin bound to spermatozoa from different bulls was significantly different (P<0 .003). However, the total H-3-heparin bound to spermatozoa was not correlat ed with any measured sperm parameter, including zona pellucida binding, emb ryo cleavage and blastocyst formation, and 56-day nonreturn rates (P>0.19). Thus, the total amount of heparin bound to the surface of spermatozoa may not be relevant to fertilizing ability. (C) 2000 by Elsevier Science Inc.