LIFELONG EFFECT OF A SINGLE NEONATAL TREATMENT WITH ESTRADIOL OR PROGESTERONE ON RAT UTERINE ESTROGEN-RECEPTOR BINDING-CAPACITY

Rats treated with a single dose of 17-beta-estradiol or progesterone within 24 h of birth were subjected to ovariectomy at 8 weeks of age and were nine days later examined for the binding capacity of the uterine estradiol receptors by saturation and competition tests (with diethylstilbestrol used as competitor). The B(max) value of the neonatally estradiol-treated rats (6.78 x 10(-10)M) was significantly decreased relative to the control (1.99 x 10(-9)M). The competition analysis affirmed these results. Neonatal progesterone treatment also accounted for a significant decrease (1.25 x 10(-9)M) in receptor concentration relative to the control (1.66 x 10(-9)M). Considering the competition analysis the decrease was less than in the case of estradiol and not even significant by saturation analysis. The uterine mass did not differ between the experimental and control rats, but part of those treated with estradiol developed ovarian cysts. It follows that not only synthetic steroids (DES, allylestrenol), but also an excessive presence of the physiological steroid hormone during the critical period of receptor maturation can account for a decrease in uterine receptor concentration in adulthood.