Estradiol Metabolism and Its Inhibition in Bull Semen

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Abstract
Bull semen was examined to determine if estradiol and testosterone were oxidized. Spermatozoa converted 14C-17[beta]-estradiol into a single product identified as estrone. The reverse reaction did not take place, nor was testosterone metabolized by the sperm. The reaction with 17[beta]-estradiol was completely inhibited by seminal plasma, so the spermatozoa had to be washed and resus-pended in Riger''s solution for the conversion to take place. The inhibition was not due to a heat-labile constituent of seminal plasma nor, apparently, to pyridine nucleotide nucleosidase in semen. Added co-factors (NAD or NADP) did not enhance the reaction in whole sperm, but did restore activity to sonified sperm. Dilute suspensions of spermatozoa were several times more active than dense suspensions. Ejaculates collected from the same bull over a 14 month period showed wide variations in ability to convert 17[beta]-estradiol, with complete lack of activity occurring in some specimens.
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