Neonatal Castration of Male and Female Rats Affects Luteinizing Hormone Responses to Estrogen During Adulthood

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Abstract
Estradiol and progesterone were measured in the maternal and fetal compartments in 6 baboons. Maternal plasma estradiol increased significantly with advancing gestation from Days 110-172 with a correlation coefficient r = 0.3978, P<0.001. In contrast, mean maternal plasma progesterone concentrations remained relatively unchanged throughout late pregnancy until after Day 173 of gestation when there was a marked increase. Maternal plasma estradiol/progesterone ratio increased progressively from 0.2 at Day 110 of gestation to 1.2 at Day 172. Estradiol and progesterone concentrations in uterine vein were usually higher than in maternal femoral vein. Amniotic fluid had lower estradiol and progesterone concentrations than did maternal and fetal circulations. Fetal blood had higher progesterone concentrations than did maternal blood suggesting fetal production of progesterone. The findings indicate that baboon pregnancy is similar to human pregnancy in showing an increase in plasma estradiol, but differs in levels of plasma progesterone. The increasing maternal plasma estradiol/progesterone ratio in the pregnant baboon may account for the increasing sensitivity of the uterus to oxytocin near term as observed by previous investigators.

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