Characteristics of (3H) Estrogen and (3H) Progestin Uptake and Effects of Progesterone on (3H) Estrogen Uptake in Brain, Anterior Pituitary and Peripheral Tissues of Male and Female Guinea Pigs1

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Abstract
In Experiment 1, whole homogenate and nuclear fraction uptake patterns of radioactivity were measured in several tissues 1, 2 and 6 h after injection of (3H) estradiol-17.beta. into gonadectomized male and female guinea pigs. In general, in both fractions the pattern of accumulated radioactivity was the same for males and females (uterus and seminal vesicle > anterior pituitary > hypothalamus cortex). A sex difference was noted in the time of peak estrogen uptake. The peak for females was at 1 h, whereas in males peak radioactivity in target tissues was observed at 2 h. Males and females showed equivalent levels of estrogen uptake in target tissues at 2 h but by 6 h, levels in males began to decline, though not significantly, to a level lower than in females. The results are consistent with a role for estrogen in central and peripheral tissues of male and female guinea pigs, and suggest a basis for the lesser sensitivity of males than females to estrogen on a variety of measures. Experiments 2 and 3 assessed whole homogenate and nuclear uptake of radioactivity in several tissues 15 min and 2 h after injection of (3H) progesterone into ovariectomized, estrogen-primed guinea pigs. Only uterus accumulated radioactivity in the nuclear fraction much above background. Negligible levels of radioactivity were accumulated in cell nuclei of the anterior pituitary, hypothalamus, midbrain and cortex. Only uterine radioactivity was saturable when animals were pretreated with an excess of unlabeled progesterone. The effect of progesterone pretreatment on whole homogenate and nuclear uptake of radioactivity 2 or 6 h after injection of (3H) estradiol-17.beta. was examined in several tissues of ovariectomized guinea pigs either primed or not primed with unlabeled estradiol-17.beta.. In no case was neural uptake of radioactivity affected by the progesterone pretreatment.