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1. Microsomal preparations from rat liver, kidney and intestine were tested for UDPglucuronyltransferase activity by using oestrone, oestradiol-17f8, oestriol, testosterone, cortisol, cortisone, corticosterone, aldosterone, tetrahydrocortisol and tetrahydrocortisone as substrates. The microsomal preparation from the liver glucuronidated oestrone, oestradiol-17fl and testosterone. 2. The specific activity of the enzyme was significantly higher in livers from female rats than in those from male rats. 3. Testosterone was actively glucuronidated by both sexes. Cortisol, cortisone, corticosterone, aldosterone, tetrahydrocortisol and tetrahydrocortisone were not glucuronidated by any of the three tissues. 4. The non-ionic detergent Lubrol WX activates liver microsomal UDP-glucuronyltransferase 2-3-fold with oestrone and testosterone as substrates. 5. Oestrone glucuronyltransferase was inhibited by oestradiol-17f, predominantly competitively and by testosterone non-competitively. Bilirubin was a non-competitive inhibitor of oestrone glucuronidation. p-Nitrophenol had no effect. 6. Oestrone glucuronyltransferase could not be stimulated by either acute or prolonged treatment of animals with phenobarbital, whereas a single dose of 3-methylcholanthrene led to a moderate stimulation. 7. Ovariectomy leads to a 56% decrease in oestrone glucuronyltransferase activity; administration of oestradiol-17f, induces the enzyme to normal activity after 12 days, and after 15 days the activity is twice the control value.Actinomycin D and cycloheximide block the oestradiol-17fi-induced increase in enzyme activity. 8. Castration has no effect on the activity of testosterone glucuronyltransferase, nor does administration of testosterone influence enzyme activity. The results provide strong evidence for the existence of multiple steroid glucuronyltransferases in the liver of the rat.Oestrogen glucuronyltransferase (UDP-glucuronate-17f,-oestradiol 3-glucuronyltransferase, EC 2.4.1.59) catalyses the transfer of glucuronic acid from UDP-glucuronate to oestrone. In studies in vitro, foreign compounds such as p-nitrophenol, o-aminophenol and phenolphthalein have often been used as substrates for glucuronyltransferases to measure enzyme activity (Dutton, 1971;Winsnes, 1973). Endogenous substrates include bilirubin (Mulder, 1972) and steroid hormones such as oestrone, oestradiol-17.8, oestriol, testosterone (Rao & Breuer, 1969;Rao et al., 1970a Rao et al., ,b, 1972Rao et al., , 1974Gotze et al., 1971) and tetrahydrocorticosterone (Miller et al., 1973). With so many different acceptors, it may be asked what degree of specificity UDPglucuronyltransferase possesses. Our own previous work with steroid substrates, and other evidence Vol. 162 (see Dutton, 1971;Jacobson et al., 1975), suggests multiplicity of the enzyme.As UDP-glucuronyltransferases are inducible (see Conney, 1967), the effects of administration of phenobarbital and 3-methylcholanthrene, two commonly used enzyme-inducing agents, on steroid glucuronyltransferases were investigated. More...

The glucuronidation of oestrone, oestradiol-17ß and oestriol by the 600 g supernatant fraction of pig liver, kidney and intestine was studied in the presence and absence of UDPglucuronic acid. All three tissues formed only the 3-glucuronides of the oestrogens incubated. The order of glucuronidation with oestrone and oestradiol-17ß as substrates was kidney/intestine> liver. The 3-glucuronides of oestrone, oestradiol-17ß and oestriol were hydrolysed at pH 5.0 by the 600 xŝ upernatant fractions of the three tissues to a considerable extent. The order of activity was liver> intestine> kidney. These studies show that liver, kidney and intestine of the pig specifically glucuronidate the phenolic hydroxyl group at C-3 of oestrone, oestradiol-17ß and oestriol and also specifically hydrolyse the 3-glucuronides. The liver exhibited significant 17ß-hydroxysteroid oxidoreductase activity, followed by the kidney, while the intestine was devoid of such activity. However, no conversion of oestrone 3-glucuronide to oestradiol-17ß 3-glucuronide or vice versa was observed.