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Fate of Radiocarbon in Beef Steers Implanted with ¹⁴C-Diethylstilbestrol

U.S. Department of Agriculture, Beltsville, Maryland 20705 and Fargo, North Dakota 58102

Abstract

Eight beef steers averaging 302 kg body weight and consuming a 70% concentrate diet ad libitum were implanted with diethylstilbestrol (DES) ear implants containing monoethyl-1-¹⁴C-DES. Two implanted steers and an untreated control steer each were slaughtered at 30, 60, 90 and 120 days after implantation. Feces, urine and blood sampled during the implant periods, tissue, bile and gastrointestinal tracts obtained from slaughtered steers, and the residual implants retrieved from the ears at slaughter were analyzed for radiocarbon content. The concentration of radioactivity in blood plasma and the excretion of radioactivity indicated an initial rapid but variable absorption of DES from the ear implants followed by a slow continual absorption of DES from 14 days after implanting to the end of the 120-day study. All implants were retrieved at slaughter; the residual implants retrieved at 120 days accounted for 16 to 19% of the administered radioactivity.

Radioactivity was not distinguishable from background in muscle tissue but was greater than background in spleen, adrenal, lung, kidney and liver tissues and in the contents of the small and large intestines for all steers. The concentration of total radioactivity in liver tissue of the steers, calculated as ppb DES equivalents, either approximated or was below the detectability limits (.5 ppb) of the routine gas chromatographic method for DES analysis; however, thin-layer- chromatography and isotope dilution techniques presumptively identified a part of the total radioactivity in liver tissue as being associated with DES or conjugates. The remainder of the radioactivity was not identified. The percentage of total radioactivity in the liver presumptively associated with DES and conjugates did not vary relative to length of implant period. Gas chromatography-mass spectrometer analysis of hydrolyzed liver extracts resulted in measurable quantities of cis and trans DES for the two livers that contained the highest concentrations of total radioactivity. The study suggested that as a result of the recommended use of DES ear implants, DES and its conjugates in animal tissue generally would not be detectable by current routine residue methods but may be detected by more sophisticated laboratory techniques.

¹ ARS, Nutrition Institute, Ruminant Nutrition Laboratory, Beltsville Agricultural Research Center, Beltsville, Maryland 20705.

² ARS, Metabolism and Radiation Research Laboratory, State University Station, Fargo, North Dakota 58102.

³ The authors gratefully acknowledge the advice and assistance of Mr. R. M. Simpson and Drs. J. E. Spaulding and A. J. Malanoski of U.S.D.A. Animal and Plant Health Inspection Service in setting up the GLC procedure for tissue analysis of DES and for duplicate analysis of tissues, the assistance of Dr. G. Samuelson for implanting the cattle and the assistance of Mr. E. E. Williams and Mr. D. F. Hucht for sample preparation and radiocarbon analysis.

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