The metabolism of [4-14C]progesterone in the cat: biliary and urinary excretion of conjugated metabolites

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Abstract
[4-14C]Progesterone has been administered intravenously to anaesthetized male cats as a single injection or as a 1 or 3 hr. infusion. Bile and urine were collected for periods of up to 6 hr. after the start of the injection, and the excretion of radioactive metabolites was determined. The major part of the dose of progesterone (up to 67.1%) was excreted in the bile, whereas in no cat did urinary excretion of metabolites exceed 1%. Bile and urine samples were hydrolysed by standard methods so that the following ether-soluble neutral fractions were obtained: nonconjugated (extractable before hydrolysis); gluc-uronide, extractable after incubation with limpet powder; cold-acid hydrolysed: hot-acid hydrolysed. In addition there was a significant quantity of metabolites remaining water-soluble after all forms of hydrolysis. When 1 or 2 hr. fractions of bile were analysed the proportion of radioactivity excreted as glucuronide always decreased in successive samples, whereas water-soluble metabolites generally increased. In some animals the proportion of cold-acid-hydrolysed metabolites increased and in others decreased. No consistent change was detectable in hot-acid-hydrolysed radioactivity. A similar trend was seen in successive urine samples. The relationship of these results to similar studies of progesterone in man and other animals is discussed.