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 etio logy of compromised zona pellucida penetration and oocyte fertilizatio n. 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 capacitate d, swim-up processed sperm to acrosome-react in response to chemical ( calcium ionophore) or physiological (solubilized zonae pellucidae) ind ucers; and 4) differences in acrosomal ultrastructure by use of transm ission electron microscopy (TEM). Acrosomal status was determined with the fluorescent probe Arachis hypogaea (peanut) agglutinin. The timin g of in vitro capacitation differed (p < 0.05) between cat populations . Normospermic samples were capacitated at 2.0 h postcentrifugation, w hereas 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 spont aneous acrosomal loss/reaction over time were similar (p < 0.05) betwe en cat groups (range, 7.6-17.8%). In swim-up separated sperm from norm ospermic cats, ionophore A23187 was a more potent inducer (p < 0.05) o f the acrosome reaction (70.1 +/- 6.5%) than solubilized zonae pelluci dae (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, 2 3.9 +/- 4.7%; p > 0.05). Sperm motility patterns over time indicated t hat 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 propor tion of sperm cells with malformed acrosomes (swim-up, 33.5 +/- 3.5%; washed, 26.6 +/- 4.6%). These results indicate that sperm from teratos permic cats exhibit a high incidence of malformed acrosomes detectable only at the ultrastructural level. Nevertheless, acrosomal dysfunctio n is not related exclusively to structural defects because > 40.0% of swim-up separated sperm with structurally normal acrosomes still are i ncapable of completing the acrosome reaction. This suggests that compr omised capacitation and acrosomal dysfunction may be responsible for l ow fertilization success in the teratospermic domestic cat.