SELENIUM AND GLUTATHIONE-PEROXIDASE DISTRIBUTION IN BOVINE SEMEN AND SE-75 RETENTION BY THE TISSUES OF THE REPRODUCTIVE-TRACT IN THE BULL

In order to compare the distribution of selenium and glutathione peroxidase (GSH-Px) in bovine semen and to determine the stage at which selenium is incorporated into bovine spermatozoa, 3 bulls were each injected with a single dose of 75Se-selenite. After injection, radioactivity and GSH-Px activity in blood and semen were monitored for a period of 75 days. For all bulls 75Se was detected in seminal plasma 6 h postinjection and levels in the seminal plasma exceeded blood levels by 24 hr postinjection. Radioactivity increased rapidly in the seminal plasma for the first 10 days following injection and then decreased slowly for the remainder of the collection period. Between Days 15 and 20 postinjection, 75Se increased in the spermatozoa. GSH-Px activity was present only in blood and seminal plasma. In a second experiment, the relative tissue retention of 75Se by the reproductive tract and other body tissues was examined in 4 bulls. Each bull received a second injection of 75Se-selenite. Bulls were slaughtered at 23 days postinjection when levels of 75Se in the semen were approximately 16 times greater than blood levels and both spermatozoa and seminal plasma were labeled. Selenium-75 retention expressed as cpm/g of tissue was determined for a total of 14 tissues. Epididymis (67,078 ± 4,787 cpm/g) and testis (33,459 ± 783 cpm/g) retained the greatest amount of 75Se with the exception of the kidney (105,439 ± 5,936 cpm/g). Among the accessory glands, the prostate (15,927 ± 1,356 cpm/g) and the seminal vesicles (12,491 ± 986 cpm/g) contained the highest levels of 75Se. Sperm concentration and 75Se were determined in each of 20 serial samples of the epididymis from the proximal caput through the distal cauda in 3 bulls. Both sperm concentration and 75Se retention changed dramatically within the caput and cauda regions and for all samples (n = 60) epididymal 75Se was correlated with sperm concentration (r=0.92, P<0.01).