Identification of progesterone and 5 alpha-dihydroprogesterone (5 alpha-DHP) in zebras by two-dimensional high-performance liquid chromatography and their dependence on the state of reproduction

Because of its low levels in late pregnancy, the relationship of progestero ne to pregnancy maintenance in Equidae is not obvious. This study investiga ted the levels of progesterone (4-pregnane-3,20-dione; P4) and 5 alpha-dihy droprogesterone (5 alpha-DHP) during pregnancy in zebras in relation to rep roductive state. Blood samples from female zebras (Equs burchelli, E, zebra hartmannae, E. grevyi) were taken at Dvur Kralove Zoo. Progesterone and 5 alpha-DHP were separated by high-performance liquid chromatography techniqu es and detected by cross-reacting antibodies. Identification of progestins was achieved by comparing the identity of peaks of the samples with a stand ard. In E, z. hartmannae progesterone, values reached 50 ng/mL at the begin ning of pregnancy and dropped to levels below 1 ng/mL during the second hal f of pregnancy. In contrast, 5 alpha-DHP increased up to 123 and 183 ng/mL during late pregnancy in E. z. hartmannae and E. burchelli, respectively. I n E. grevyi, 5 alpha-DHP levels of 368 ng/mL were obtained during pregnancy , whereas progesterone values were similar in pregnant and non-pregnant ind ividuals. These marked differences in the course of progesterone and 5 alph a-DHP levels point to the importance of 5 alpha-DHP for pregnancy maintenan ce in zebras. Zoo Biol 18:325-333, 1999. (C) 1999 Wiley-Liss, Inc.