Biology of Reproduction 58, 60-64
The modulatory effects of gestational age and circulating concentrations of progesterone, 5-pregnane-3,20-dione, and estradiol-17 on the uterine sex steroid hormone receptor levels of the African elephant were investigated. Uterine tissue biopsies and blood samples were obtained from animals culled in the Kruger National Park. Estrogen and progesterone receptor concentrations were determined in uterine biopsies from subadult, lactating, early-, mid-, and late-pregnant elephants, by equilibrium binding assays. Circulating estradiol-171 and progesterone concentrations were measured by means of RIAs, while plasma concentrations of 5-pregnane-3,20-dione were determined with an amplified ELISA. Significant inverse correlations of the concentrations of estrogen and progesterone receptors with the gestational stage of the elephants were observed.