Sperm capacitation and the acrosome reaction are compromised in teratospermic domestic cats

The efficiency of sperm capacitation and of the acrosome reaction was studied in the teratospermic domestic cat to evaluate further the etiology of compromised zona pellucida penetration and oocyte fertilization. Specific objectives were to compare normospermic and teratospermic cat ejaculates for 1) the kinetics and timing of sperm capacitation in vitro as determined by an ionophore-induced acrosome reaction; 2) the incidence of spontaneous acrosomal loss; 3) the ability of capacitated, swim-up processed sperm to acrosome-react in response to chemical (calcium ionophore) or physiological (solubilized zonae pellucidae) inducers; and 4) differences in acrosomal ultrastructure by use of transmission electron microscopy (TEM). Acrosomal status was determined with the fluorescent probe Arachis hypogaea (peanut) agglutinin. The timing of in vitro capacitation differed (p < 0.05) between cat populations. Normospermic samples were capacitated at 2.0 h postcentrifugation, whereas teratospermic samples required 2.5 h to become capacitated. At 2.5 h, sperm from teratospermic males were less capable (p < 0.05) of completing the acrosome reaction after ionophore exposure (49.3 +/- 8.0%) than sperm from normospermic males (73.3 +/- 3.8%). Levels of spontaneous acrosomal loss/reaction over time were similar (p > 0.05) between cat groups (range, 7.6-17.8%). In swim-up separated sperm from normospermic cats, ionophore A23187 was a more potent inducer (p < 0.05) of the acrosome reaction (70.1 +/- 6.5%) than solubilized zonae pellucidae (31.1 +/- 1.2%). Swim-up separated sperm from teratospermic cats, however, were compromised in the ability to acrosome react, regardless of inducer (ionophore, 23.9 +/- 3.3%; solubilized zonae pellucidae, 23.9 +/- 4.7%; p > 0.05). Sperm motility patterns over time indicated that differences in acrosomal status were not influenced by cell death. The frequency of abnormal acrosomes detected by TEM was higher (p < 0.05) in teratospermic (30.0 +/- 3.9%) than in normospermic (3.1 +/- 1.3%) samples. Swim-up separation failed to reduce (p > 0.05) the proportion of sperm cells with malformed acrosomes (swim-up, 33.5 +/- 3.5%; washed, 26.6 +/- 4.6%). These results indicate that sperm from teratospermic cats exhibit a high incidence of malformed acrosomes detectable only at the ultrastructural level. Nevertheless, acrosomal dysfunction is not related exclusively to structural defects because > 40.0% of swim-up separated sperm with structurally normal acrosomes still are incapable of completing the acrosome reaction. This suggests that compromised capacitation and acrosomal dysfunction may be responsible for low fertilization success in the teratospermic domestic cat.