Temporal changes in serum estradiol and prolactin in immature female rats given a single injection of estradiol benzoate

Serum concentrations of estradiol 17β(E₂) measured by immunoassay reached peak levels (100pg/ml) within one hour in immature female rats given a subcutaneous injection of lug 17βestradiol-3-benzoate (EB). Hypophysectomy did not alter the E₂ concentration, but lower peak levels were found in ovariectomized females. In animals with ovaries a secondary rise in serum E₂ was apparent 12 hours after the injection of EB; from 12 to 48 hours E₂ decreased linearly. A dose of Bug EB caused an abrupt rise in E₂ (180pg/ml) within 30 minutes, but during the next 24 hours rather wide fluctuations in serum levels were found. In animals acclimated to a reversed light schedule and given 5ug EB early in the dark period, E₂ decreased linearly over a period of 72 hours. Prolactin increased in response to the E₂: a rhythm was suggested by the occurrence of increases during the dark periods. The results indicate that statistically significant fluctuations in both E₂ and prolactin occur after a single injection of EB and that measurements at a single point in time are inadequate to determine the true pattern of hormonal changes.