| Experiments were designed to determine optimum conditions and factors affecting the in vitro capacitation of Siberian tiger (Panthera tigris altaica) sperm. Electroejaculates and serum samples were collected throughout the year from 5 tigers. Ejaculates were either assayed fresh or after being cryopreserved. Sperm were able to penetrate zona-free hamster ova after 2 h preincubation in Biggers, Whitten & Whittingham's medium at 37;Season had no effect on the semen production and quality of captive male Siberian tigers as measured by semen volume, concentration, motility, morphology, viability and ability to undergo capacitation. Seminal plasma levels of acid phosphatase, calcium, glucose, potassium and phosphorus were not affected by season. Serum levels of testosterone were highest in fall and early winter but were not correlated with semen quality.;Tiger SP contained 4 soluble antigens detectable by immunodiffusion. At least one was SP specific, and 2 crossreacted with domestic cat reproductive tissues and fluids. Tiger sperm contained 2 soluble antigens and both were shared with domestic cat testis and epididymis. Antigenic crossreactivity between these species supports the use of the domestic cat as a model for tiger reproductive research.;Tiger and bull sperm were able to capacitate in neat, but not in concentrated, tiger SP, while bull sperm capacitated in diluted, but not in neat bull SP. Heating neat bull SP and concentrated tiger SP did not destroy their capacitation inhibiting activity. Bull sperm, incubated in a tiger SP fraction containing proteins of 43,000 daltons, did not capacitate while those incubated in SP fractions containing molecules both larger and smaller became capacitated. SDS-PAGE of neat tiger SP under reducing conditions showed bands of 68,000 and 28,000 daltons, while concentrated tiger SP revealed 7 polypeptide bands of 68,000, 58,000, 54,500, 42,000, 28,000, 24,000 and 19,000 daltons. |
