METABOLISM OF [14C]ETHYNYLOESTRADIOL IN THE BABOON

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Abstract
SUMMARY: The amounts of radioactivity in the plasma and in the urine of two normally cycling baboons was studied after intravenous administration of [14C]ethynyloestradiol labelled in the ethynyl side-chain. Within 6 days 76·9–83·3% of the dose was excreted in the urine; 36·4–50·9% appeared on the day of injection, and radioactivity continued to be excreted to the extent of 2·4–2·9% even on day 6. Of the urinary conjugates isolated by neutral resin chromatography, enzymic hydrolysis and solvolysis liberated 57·2–70·5% and 14% of radioactivity respectively. Paper chromatography of the β-glucuronidase-liberated fraction with an intact ethynyl group suggested the presence of at least 11 metabolites. Peaks of radioactivity were found among the more polar compounds which barely moved from the starting line, and among compounds similar in polarity to the administered steroid. The chromatographic results with the metabolites suggest that hydroxylation is an important metabolic pathway for ethynyloestradiol in the baboon.

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