Morphological change of the acrosome on motile bovine spermatozoa due to storage at 4°C

Abstract

Swelling of the apical ridge and anterior acrosome of motile bovine spermatozoa was observed during in-vitro storage using differential interference-contrast optics. This morphological alteration is different from that described as the false acrosome reaction on immotile spermatozoa, apparent in aging semen samples and which has been associated with cell death. In this study, transmission electron microscopy revealed that the apical ridge acrosomal matrix was extended into complex folds and/or projections. Acrosomal and plasma membrane integrity was retained. Storing spermatozoa (1500 x 106/ml) in seminal plasma at 4°C for 1 day was most conducive to thw swelling of the apical ridge. Replacing seminal plasma with egg yolk-citrate inhibited swelling. However, incubating semen at 37°C in egg yolk-Tris-fructose extender (25 x 106 spermatozoa/ml) after storage in egg yolk-citrate at 4°C for ≥3 days restored the swelling characteristic.