Showing papers by "R. J. van Aarde published in 1998"
Journal Article•
33 citations
TL;DR: Results are in agreement with those obtained from the golden spiny mouse Acomys russatus and support the idea that small diurnal mammals retain the Tb rhythm of a nocturnal rodent and suggest that pineal melatonin secretion in these rodents is regulated by α rather than by β receptors.
16 citations
TL;DR: It is concluded that the progesterone receptor concentrations are down-regulated with progressing gestation in the African elephant, and appears to be linked to an increase in circulatory 5alpha-pregnane-3,20-dione concentration in the plasma of pregnant animals.
Abstract: 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. 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 correlation existed between uterine estrogen and progesterone receptors levels. Circulating concentrations of 5a-pregnane-3,20dione and progesterone decreased with an increase in the concentrations of progesterone receptors as well as with fetal age. We conclude that the progesterone receptor concentrations are down-regulated with progressing gestation in the African elephant. This down-regulation appears to be linked to an increase in circulatory 5-pregnane-3,20-dione concentration in the
7 citations