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Endogenous Estrogens in Bovine Tissues^{1 ,2,}

Clemson University^,4, Clemson, SC 29631

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-17ß(E₂ß) + estrone (E₁)⁵ and one for E₂ß. 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 E₂ß-³H, averaged 87%. The reagent blank was 4.8 ± .3 pg (mean ± SE) for all assays for E₂ß and 10.1 ± .7 pg for all assays for the estrogens. Recovery of E₂ß 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 E₂ß 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 E₂ß 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 E₂ß 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 (E₂ß+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.

¹ Presented as part of the Symposium on Natural Hormones in Edible Animal Products held during the A.S.A.S. Annual Meeting at Texas A&M University, August 16, 1976. Publication supported in part by DHEW/PHS/FDA/BVM contract No. 221-76-0129.

² Technical Contribution No. 7973 of the South Carolina Agricultural Experiment Station, Clemson University, Clemson 29631.

³ The authors acknowledge the technical assistance of Sarah A. Bailey and the advice of Mr. Joseph Toler on the statistical analysis. Gifts of antiserum from Dr. B. V. Caldwell of Yale University and Dr. D. Collins of Emory University are gratefully acknowledged.

⁴ Department of Food Science.