INFLUENCE OF GESTATION ON UTERINE ENDOMETRIAL STEROID-RECEPTOR CONCENTRATIONS IN THE AFRICAN ELEPHANT, LOXODONTA-AFRICANA

The modulatory effects of gestational age and circulating concentratio ns of progesterone, 5 alpha-pregnane-3,20-dione, and estradiol-17 beta on the uterine sex steroid hormone receptor levels of the African ele phant were investigated. Uterine tissue biopsies and blood samples wer e obtained from animals culled in the Kruger National Park, Estrogen a nd progesterone receptor concentrations were determined in uterine bio psies from subadult, lactating, early-, mid-, and late-pregnant elepha nts, by equilibrium binding assays. Circulating estradiol-17 beta and progesterone concentrations were measured by means of RIAs, while plas ma concentrations of 5 alpha-pregnane-3,20-dione were determined with an amplified ELISA, Significant inverse correlations of the concentrat ions of estrogen and progesterone receptors with the gestational stage of the elephants were observed, Pregnant uterine horns of individual animals contained lower levels of estrogen and progesterone receptors than the nonpregnant horns of the same animals. A strong positive corr elation existed between uterine estrogen and progesterone receptors le vels. Circulating concentrations of 5 alpha-pregnane-3,20-dione and pr ogesterone decreased with an increase in the concentrations of progest erone receptors as well as with fetal age. We conclude that the proges terone receptor concentrations are down-regulated with progressing ges tation in the African elephant, This down-regulation appears to be lin ked to an increase in circulatory 5 alpha-pregnane-3,20-dione concentr ation in the plasma of pregnant animals.