Endogenous Estrogens in Bovine Tissues

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Abstract
The purpose of this study was to develop a method of extraction, purification and assay for estrogens in bovine muscle, kidney, liver and uterine endometrium. Assays were developed to obtain two estrogen concentrations for a tissue: one for estradiol-17β(E2β) + estrone (E1)5 and one for E2β. Homogenization of the tissue was followed by extraction with ethyl ether, a four-step solvent partition procedure and submission of the extract to a routine radioimmunoassay. Extraction of estrogens from the four tissues, based on use of E2β-3H, averaged 87%. The reagent blank was 4.8 ± .3 pg (mean ± SE) for all assays for E2β and 10.1 ± .7 pg for all assays for the estrogens. Recovery of E2β added to the tissues demonstrated that the assays were accurate and precise. The coefficients of variation for the same tissue sample assayed in six assays were 12.2% for the E2β assay and 9.2% for the estrogen assay. With respect to estrogen concentrations, the tissues ranked in the following order compared to muscle which was lowest: uterine endometrium (10-fold higher), liver (fivefold) and kidney (fourfold). The ratio of E2β to E1 was 2:1 in liver, kidney and pro- and post-estrous phase endometrium, and 1:1 in muscle and luteal phase endometrium. The levels of estrogen in muscle were not significantly different (P>.05) between steers and heifers. Estrogen levels in liver and kidney were significantly greater (P<.05) in heifers than in steers. In heifers, pre- and post-estrous phase endometrium contained significantly greater concentrations of the estrogens and E2β than luteal phase endometrium (P<.05); mean levels in the edible tissues were not significantly different (P>.05) for each of the four stages of the estrous cycle at which heifers were slaughtered. The mean estrogen levels (E2β+E1) in steers were significantly greater 60 days after initiation of the experiment than on days 30 and 90 (P<.01) indicating the possibility of significant variation in tissue estrogen levels in a population of untreated animals. Copyright © 1977. American Society of Animal Science . Copyright 1977 by American Society of Animal Science.

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