Steroid glucuronyltransferases of rat liver. Properties of oestrone and testosterone glucuronyltransferases and the effect of ovariectomy, castration and administration of steroids on the enzymes

Abstract

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...

Ursodeoxycholate Reduces Ethinylestradiol Glucuronidation in the Rat: Role in Prevention of Estrogen-Induced Cholestasis

“…The protein content of microsomal preparations was determined by the biuret method (Gornall et al, 1949). 17␤-Glucuronidation of EE was assessed according to Rao et al (1977), except that microsomes were activated with UDP-N-AG (2.0 mM final concentration). A trace amount of [ 3 H]EE was added along with unlabeled EE (1 mM).…”

Interference of UDP-Glucuronyltransferase and β-Glucuronidase Activity in Rat Liver Microsomes at pH 7.5 with p-Nitrophenol and p-Nitrophenylgliicuronide as Substrates

“…The aim of this work was to determine activities of GT and ß-G at the liver microsomal level under identical experimental conditions, and at physiological pH. Since GT has been claimed to be present in multiple substrate-specific species (20,21,26), the one substrate pair p-nitrophenol, and p-nitrophenylglucuronide, has been used.…”

Androgen Regulation of Renal Uridine Diphosphoglucuronosyltransferase 1A1 in Rats: Fig. 1.

“…For example, transcription of UGT1A1 and 1A6 mRNA in rat Sertoli cells is up-regulated in response to testosterone treatment (Magnanti et al, 2000). Additionally, there are many examples of sex differences in rat glucuronidation, such as for mycophenolic acid glucuronidation in vivo (Stern et al, 2007), phenol red glucuronidation in vivo (Hart et al, 1969), p-nitrophenol glucuronidation in vivo and in renal microsomes (Rush et al, 1983), and 17␤-estradiol in hepatic microsomes (Rao et al, 1977). In some cases these sex differences may be due to factors other than UGT isoform transcription, such as differences in post-translational UGT modification, substrate absorption, cosubstrate abundance, competing metabolic pathways, or metabolite excretion.…”