Metabolism and excretion of oestradiol-17β and progesterone in the Sumatran rhinoceros (Dicerorhinus sumatrensis)

3H-labelled oestradiol-17β and 14C-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 steroid, 68% of 3H-oestradiol and 89% of 14C-progesterone were recovered. Peak excretion in urine occurred on day 1 for both steroids, and for faeces on day 2 for 14C-progesterone, and between days 2 and 3 for 3H-oestradiol. Oestradiol metabolites were predominantly (nearly 70%) excreted into the urine, while progesterone metabolites were almost exclusively (>99%) excreted into the faeces. The majority (>70%) of urinary 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-soluble (i.e., unconjugated) forms. HPLC co-chromatography of oestrogens in hydrolysed urine indicated only one peak of radioactivity, co-eluting with authentic oestradiol-17β, whereas two peaks of radioactivity were found after HPLC of faecal oestrogens, the major one co-eluting with oestrone and the less prominent one with oestradiol-17β. Progesterone was excreted as numerous metabolites into the faeces. The three most abundant of these were identified using HPLC and gas chromatography mass spectrometry (GCMS) as 5β-pregnane-3α,20α-diol, 5β-pregnane-3α-ol-20-one, and a second pregnanediol, the exact structure of which could not be deduced. Measurement of urinary oestradiol-17β and faecal immunoreactive pregnanediol and 5α-pregnane-3α-ol-20-one in daily samples enabled the first endocrine characterization of the ovarian cycle and indicated a cycle length of ∼25 days.