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 Eo (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.
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