PROGESTERONE AND OESTRADIOL RECEPTORS IN THE UTERUS OF OESTRADIOL-PRIMED FETAL AND NEWBORN GUINEA-PIGS

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Abstract
The responsiveness of the uterus of the guinea-pig to oestrogen treatment was studied in the fetal and perinatal periods. Twenty-four hours after one dose of 1 mg oestradiol/kg body wt to the pregnant guinea-pig, there was no significant increase in uterine wet weight of the fetus but a sevenfold increase in the concentration of progesterone receptors. In the perinatal period, doses of 1,10 and 100 μg oestradiol led to as much as an 80% increase in uterine wet weight after 24 h in both 2- and 7-day-old guinea-pigs. On the other hand, levels of progesterone receptors in newborn animals showed a smaller increase (twofold) than that which occurred in the fetal uterus. In both fetal and newborn guinea-pigs, total oestradiol-receptor concentrations (both available and occupied binding sites) decreased significantly after treatment with oestradiol. It was concluded that the hormonal effect of oestradiol on progesterone-receptor synthesis can be expressed in the fetus and to an even greater extent than in the perinatal period over the same period of time. In the fetus, this response can be distinguished from the overall uterotrophic effect of oestradiol.