Dynamics of estrone glucosiduronate metabolism in dogs

Interest in the metabolism of estrogen conjugates has been increased by the recent demonstration that some of these conjugates can be hydrolysed in vivo, and are thus a source of physiologically-active circulating estrogens. In this report the metabolism of the quantitatively important conjugate estrone glucosiduronate has been studied in dogs, following the intravenous infusion of 3H-estrone glucosiduronate. Arterial plasma levels of radioactive estrone glucosiduronate and of the radioactive metabolites estrone, estradiol-17beta-3-glucosiduronate and estradiol-17alpha-3-glucosiduronate were measured. The metabolic clearance rate of estrone glucosiduronate (MCREG) was determined, as well as conversion ratios for estrone glucosiduronate to estrone (CREG.E), estradiol-17beta-3-glucosiduronate (CREG.E2betaG) and estradiol-17alpha-3-glucosiduronate (CREG.E2alphaG). Sequential values for the above mentioned conversion ratios were obtained and the relationship to time was analysed. Transfer constants for estrone glucosiduronate to estrone (rhoEG.E) were measured. The mean MCREG was 329 L/day/m2, SE 35. The values for CREG.E2betaG and CREG.E2alphaG did not become constant until 80 minutes following the start of infusion. The mean values at a steady state were: CREG.E.021, SE .002, CREG.E2betaG .068, SE .005, CREG.E2alphaG .022, SE .002. The mean value for rhoEG.E was .057, SE .006.