Effects of Progesterone on Uptake and Retention of ³H-Testosterone in the Neonatal Female Rat

Abstract

Radioactivity concentrations in digested skeletal muscle and extracts of the cerebral cortex and hypothalamus were determined at 15, 30, 60, 90, 120, 150, 180, 210, 240, 270 and 300 min, following injections of 0.05 µg ³H-testosterone (specific activity 190 µCi/µg) in 3-day-old female Sprague-Dawley rats. One-half of the animals also received 3 mg progesterone immediately prior to the radiochemical. Progesterone treatment did not significantly affect the ³H concentrations in the hypothalamus and muscle; however, it significantly raised the ³H concentrations in the cerebrum. The radioactivity in the muscle samples was significantly higher than in the brain at all intervals except 15 min. The hypothalamic radioactivity was not significantly different from the radioactivity in the cortex in either the progesterone-treated or control animals. The ³H-testosterone concentrations, determined by thin-layer chromatography, were the same in both brain regions for the 2 h tested. In the samples from control animals, ³H-testosterone was maximal at 30 min; the same peak values were observed 30 min later in the progesterone-treated animals. The significant increases in ³H concentrations in the cerebra of the progesterone-treated animals were the result of an increase in nonpolar metabolites, not in ³H-testosterone. AH ³H-testosterone values steadily diminished with time. The data indicate that preferential uptake and retention of unmetabolized testosterone by the hypothalamus of the 3-day-old rat do not accompany its differentiating action upon this region and that progesterone does not exert its protective effect by altering distribution of the androgen.