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Metabolic Fate of Orally Administered Estradiol in Swine^{1 ,2 ,3,}

Purdue University^,6, West Lafayette, IN 47907

Abstract

These studies were undertaken to determine the fate of varying amounts of ¹⁴C-estradiol-17ß (¹⁴C-E₂) after oral administration to swine. Tranquillized female pigs (5 to 6 weeks old) were given either .04, .4, 4 or 40 µmoles of ¹⁴C-E₂ via stomach tube, and blood samples were collected from previously implanted jugular cannulae at several time intervals during the first four hours after administration. The gilts were necropsied 4 hours post-treatment and the entire gastrointestinal tract was removed. Free and conjugated estrogens were isolated from the plasma and intestinal chyme. Conjugated estrogens were cleaved by three successive treatments: enzyme, solvolysis and acid hydrolysis. The free estrogens were then identified by their chromatographic mobilities in thin-layer, column- and gas-liquid chromatographic systems, and by recrystallization to constant specific activity.

Conclusions based on these studies are that plasma concentrations of radioactive estrogens were very high within 7 min after oral administration of ¹⁴C-E₂. Estradiol was completely conjugated during absorption and its first pass through the liver. The major steroid conjugates present in plasma regardless of dose were monoglucuronides (>88%), monosulfates (<8%) and diconjugates (<2%). The principal monoglucuronides in plasma were estrone glucuronide (82%), estradiol glucuronide (16%) and estriol glucuronide (3%). The principal monosulfates in plasma were estrone sulfate (52%), estradiol sulfate (34%) and estriol sulfate (16%). The proportion of E₂ converted to estrone and the proportion of estrogens conjugated decreased with increasing dose, indicating saturation of responsible enzyme systems of decreased solubility.

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 Paper No. 6357, Agricultural Experiment Station, Purdue University, West Lafayette, IN. Research supported by DHEW/Public Health Service, Food and Drug Administration, Contract 74-136.

³ The authors appreciate the assistance provided by the Project Officers, Dr. George Graber and Dr. Dave Batson. Thanks is also expressed to Anne Hollister, Martha Johnson, and Karen Gooding for technical assistance.

⁴ Present address: Food and Drug Administration, Rockville, MD.

⁵ Department of Biochemistry.

⁶ Department of Veterinary Physiology and Pharmacology.