Estrogen metabolism in the Asian elephant (<i>Elephas maximus</i>)

Abstract

Abstract Estradiol‐17β metabolism was studied in two female Asian elephants ( Elephas maximus ). In an initial study, 500 μCi of tritiated estradiol‐17β was injected iv into a single animal, and 0, 30 and 60 min serum samples were collected as well as all excreted urine and feces for 24 hr. In a second study, 1.5 mg unlabeled estradiol‐17β was injected iv into a second animal and 0, 5, 15, 30, and 60 min serum samples and a 30 min urine sample were collected postinjection. Analyses of samples from both studies demonstrated a rapid conversion of free estradiol to conjugated forms in the serum. The first (5 min) serum sample following the injection of unlabelled estradiol contained unconjugated estradiol: conjugated estradiol: conjugated estrone at a ratio of 60: 29: 10, respectively, and at 30 min a ratio of 33: 43: 24. The urinary estrogen metabolites were in the conjugated form with an estradiol: estrone ratio of 60: 40. No radiolabeled estrogen was found in the fecal samples during the 24 hr following administration of the radiolabeled estradiol. These data indicate a rapid clearance of circulating free estradiol in the elephant, with a major metabolite in the serum and urine being estradiol conjugate. © 1992 Wiley‐Liss, Inc.