METABOLISM AND EXCRETION OF ESTRADIOL-17-BETA AND PROGESTERONE IN THESUMATRAN RHINOCEROS (DICERORHINUS SUMATRENSIS)

H-3-labelled oestradiol-17 beta and C-14-progesterone were injected i. v. into an adult female Sumatran rhinoceros (Dicerorhinus sumatrensis) and all urine and faeces collected over 4 days. Of the injected stero id, 68% of H-3-oestradiol and 89% of C-14-progesterone were recovered. Peak excretion in urine occurred on day I for both steroids, and for faeces on day 2 for C-14-progesterone, and between days 2 and 3 for H- 3-oestradiol. Oestradiol metabolites were predominantly (nearly 70%) e xcreted into the urine, while progesterone metabolites were almost exc lusively (> 99%) excreted into the faeces. The majority (> 70%) of uri nary excreted oestrogens consisted of water-soluble (i.e., conjugated) forms, with > 90% of these being glucuronides. In contrast, > 75% of faecal oestrogen and progesterone metabolites were excreted as ether-s oluble (i.e., unconjugated) forms. HPLC co-chromatography of oestrogen s in hydrolysed urine indicated only one peak of radioactivity, co-elu ting with authentic oestradiol-17 beta, whereas two peaks of radioacti vity were found after HPLC of faecal oestrogens, the major one co-elut ing with oestrone and the less prominent one with oestradiol-17 beta. Progesterone was excreted as numerous metabolites into the faeces. The three most abundant of these were identified using HPLC and gas chrom atography mass spectrometry (GCMS) as 5 beta-pregnane-3 alpha,20 alpha -diol, 5 beta-pregnane-3 alpha-ol-20-one, and a second pregnanediol, t he exact structure of which could not be deduced. Measurement of urina ry oestradiol-17 beta and faecal immunoreactive pregnanediol and 5 alp ha-pregnane-3 alpha-ol-20-one in daily samples enabled the first endoc rine characterization of the ovarian cycle and indicated a cycle lengt h of similar to 25 days. (C) 1998 Elsevier Science B.V. All rights res erved.