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The University of Wyoming, Laramie and Colorado State University, Fort Collins
Abstract
In experiment 1, six yearling steers (172 to 215 kg) and six yearling heifers (215 to 256 kg) received 11 daily injections of either 1 mg estradiol-17ß or 1 mg estradiol-17ß-3-benzoate. On days 12, 13, and 14, three steers and three heifers received daily injections of 200 µCi (1 mg) of 4-14C-estradiol-17ß. The remaining heifers and steers received 312 µCi (2.15 mg) of 4-14 C-estradiol-17ß-3-benzoate. In experiment 2, two slaughter weight steers (377 and 366 kg) and two slaughter weight heifers (396 and 425 kg) received 12 daily injections of 1 mg estradiol benzoate. On day 13, the animals received 720 µCi (3.24 mg) of 4-14 C-estradiol-17ß-3-benzoate followed 24 hr later by a second injection of 1080 µCi (4.9 mg) of the hormone. Major metabolites of the radioactive estrogens were identified in muscle, fat, liver, kidney and blood samples obtained 3 hr after the final injection. Estradiol benzoate was not detected in any of the tissues analyzed with the exception of a small quantity in blood. The major metabolite in muscle was estradiol-17ß (38% to 70% of extracted radioactivity) following injection of either estradiol-17ß or estradiol benzoate. Estrone accounted for 17% to 45% of the extracted radioactivity. Aging muscle for 14 days tended to reduce (P<.1) levels of estra-diol-17ß and increase (P<.05) levels of estrone compared to aging for 3 days. The pattern of metabolites in fat was similar to that for muscle except that cooking decreased (P<.05) the level of estradiol-17ß and increased (P<.05) the level of estrone. The largest concentrations of radioactivity occurred in liver and kidney. The major estrogenic metabolites in kidney were estradiol-17
, estradiol-17-glucuronide, estradiol-17ß and estrone. In liver, the major metabolite, accounting for about 40% of the extracted radioactivity, was obtained in a chromatograph-ically homogeneous fraction, the identity of which is unknown. Estradiol-17ß, estrone, estriol and estrogen glucuronides accounted for lesser amounts of radioactivity in liver.
Metabolite levels of exogenous estrogens in cooked, aged muscle tissue in this study were 161 to 225 pg of estradiol-17ß/g of tissue and 40 to 86 pg/g for estrone. Levels of estradiol-17ß and estrone were about three and five times greater in fat. These levels are low even though the tissues were collected when residual levels of metabolites were maximal. These data suggest, therefore, that residual levels of estrogens, previously administered as anabolic agents to growing or finishing cattle, would be extremely low in muscle and fat. Higher levels and a greater variety of metabolites would be expected in liver and kidney.
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 Journal Article RJ109 from the Wyoming Agriculture Experiment Station. This research was supported by FDA contract 73-243. Send reprint requests to Dr. T. G. Dunn, Division of Animal Science, University of Wyoming, Box 3354, University Station, Laramie, WY 82071.
3 Division of Animal Science, University of Wyoming.
4 Department of Physiology and Biophysics, Colorado State University.
5 The authors gratefully acknowledge the assistance of Drs. W. F. Tucker, R. B. Staigmiller, T. Reimers and D. B. Batson.
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