Metabolism of oestradiol-17 and progesterone in the white rhinoceros (Ceratotherium simum simum)

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Abstract
14C-Labelled oestradiol-17.beta. and progesterone (50 .mu.Ci each) were injected i.v. into an adult female white rhinoceros and all urine and faeces collected separately over the next 4 days. The total recovery of injected label was 61%, 25% being present in the urine and 36% in the faeces. Of the radioactivity recovered, 69% was excreted on Day 2 of the collection period. Repeated extraction of samples obtained on Day 2 showed that, of the radioactivity in faeces, 92.4% was associated with unconjugated steroids whereas in the urine the proportion of conjugated an unconjugated steroids were similar (41.2% and 51.4% respectively). After phenolic separation of urinary steroids, HPLC followed by derivatization and recrystallization techniques identified progesterone as the major component of the unconjugated portion with 4-pregnen 20.alpha.-ol-3-one as the principal metabolite in the conjugated fraction. Pregnanediol was not present. Oestrone appeared to be the most abundant oestrogen metabolite with smaller but significant amounts of oestradiol-17.beta. and oestradiol-17.alpha. in the unconjugated and conjugated fractions respectively. Small amounts of progesterone were found in the faecal extract in which the radioactivity consisted mainly of oestradiol-17.alpha. and oestradiol-17.beta.. The results have established the major excreted metabolites of oestradiol-17.beta. and progesterone in the white rhinoceros and the development of more appropriate assay methods for monitoring ovarian function in African rhinoceroses should now be possible.