THE METABOLISM OF PROGESTERONE BY ANIMAL TISSUES IN VITRO. SEX AND SPECIES DIFFERENCES IN CONJUGATE FORMATION DURING THE METABOLISM OF (4-14C)PROGESTERONE BY LIVER HOMOGENATES.

1. Sex and species differences during the metabolism of [4-(14)C]progesterone by liver homogenates from rat, rabbit, guinea pig and hamster have been investigated. 2. Liver homogenate from male rat formed ;water-soluble' metabolites faster and in significantly larger amounts than did liver homogenate from female rat. About 65-70% of the added progesterone was conjugated as glucuronide by liver homogenate from male rat and about 45-50% by that from female rat. Liver homogenate from male rat also formed glucuronides faster than did liver homogenate from female rat. Sulphate formation was low (8-16%) in liver homogenates from both male and female rats. 3. Hamster-liver homogenate did not show any sex difference in the rate of formation of ;water-soluble' metabolites, but a sex difference was observed in the amount of free steroids recovered at low tissue:steroid ratios. Liver homogenate from female hamster formed glucuronides faster and in significantly larger amounts than did liver homogenate from male hamster, the reverse of what was found in rat liver. 4. Liver homogenates from male and female rabbits and guinea pigs formed ;water-soluble' metabolites that were almost entirely glucuronides. 5. Neither rabbit liver nor guinea-pig liver showed any significant sex difference in the rate or amount of formation of total ;water-soluble' metabolites or glucuronides, but guinea-pig liver was considerably less active than rabbit liver. 6. Glucuronides were quantitatively the major type of conjugate formed by the liver homogenates from both sexes of all species except the male hamster.