Brief Report: Differential oxidations of estradiol-17β by the chimpanzee in vivo

The metabolism of estradiol-17β is primarily an oxidative process at either carbon-2 or carbon-16 in the human. The objective of this study was to determine the relative importance of these two oxygenation pathways in the chimpanzee. The rate of oxidation of estradiol-17β at each position was determined by measuring the release of tritium into body water from carbon-2 or carbon-16. [2-³H]-Estradiol-17β or [16-³H]-estradiol-17β was injected intravenously into three adult male chimpanzees, and blood samples were obtained at several time intervals between 1 and 48 hr. The blood was lyophilized, and the release of tritium from the specifically labeled estrogens into the body fluid pool was determined. The release of tritium from the 16α-position was very low and did not exceed 3% in any animal. The release of tritium from the carbon-2 was much faster, amounting to 29%, 34%, and 35%, respectively, by 24 hr. The ratio of tritium released from carbon-2:carbon-16 was 5.0, 13.2 and 16.9, respectively, at 24 hr after injection of the specifically labeled estradiol-17β. These results demonstrate clearly that the major pathway for oxidative metabolism of estradiol-17β in the chimpanzee is via oxygenation at carbon-2, with the formation of catechol estrogens, as in the human.