Estrogen levels in immature female rats: True or spurious-ovarian or adrenal?

Using radioimmunoassay (RIA) to determine the levels of estradiol (E₂) and estrone (E₁) in sera from immature female rats between 1-24 days of age, extremely high values were obtained. Maximum levels for E₂ were found at 10 and 18 days and for E₁ at 10 days. (E₂ day 10, mean = 2235 pg/ml, range 924-5500; day 18, mean = 1691 pg/ml, range = 282-1898. E₁: day 10, mean = 1060 pg/ml, range = 282-1898 pg/ml.) An injection of 100 Hg testosterone propionate (TP) at 5 days of age suppressed the peaks of E₂ and E₁(Values obtained for E₂ in aliquots from a single pool of serum measured by RIA, by protein binding using uterine cytosol and by double isotope derivative methods were 3000 pg/ml, 170 pg/ml, and 82 pg/ml, respectively, indicating that the bulk of the displacement in the RIA was due to substances other than E_o (spurious E₂). In contrast the values obtained by the 3 assay techniques for E, were similar (940 pg/ml, 1045 pg/ml, and 780 pg/ml, respectively). To determine the source of the spurious E₂ and of the E₁ rats were ovariectomized, adrenalectomized or ovariectomized and adrenalectomized at 6, 14 or 20 days of age. Circulating E₂ and E₁ were measured 4 days postoperatively by RIA. Only adrenalectomy caused significant reduction in E₂ and E₁ implicating the adrenal as their major source. The levels of E₂and E₁ were lower in ovariectomized females that had been injected with TP on day 5 than in sesametreated ovariectomized controls, indicating an effect of the TP on the adrenals.