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Metabolism of Estrogens in the Gastrointestinal Tract of Swine. I. Instilled Estradiol^1,2,3,

Purdue University², West Lafayette, IN 47907

Abstract

One minute after instillation of ¹⁴C-estradiol-17ß (¹⁴C-E217ß) into selected sections of the gastrointestinal tract of swine, radioactive estradiol metabolites were present in blood collected from the portal and jugular veins. Ether was used to extract free but not conjugated estrogens. The percentage of plasma radioactivity that was ether extractable (EE) was low in portal plasma and even lower in jugular plasma following instillation of ¹⁴C-E₂17ß into the stomach, ileum and colon. EE radioactivity was not detectable in either portal or jugular plasma when estradiol was instilled into the duodenum or jejunum. Therefore, estrogens were conjugated either in the lumen of the gastrointestinal tract or as they crossed the intestinal mucosa. The liver played only a minor role in conjugation of these steroids, since the estrogen metabolites present in portal plasma were very similar to those in jugular plasma, and metabolites in the urine were similar to those in plasma. The principal estrogen conjugate found in both portal and jugular plasma, regardless of the gastrointestinal section into which ,¹⁴C-E₂ 17ß was instilled, was estrone glucuronide. There was no uniform metabolic pattern observed in the metabolites of estradiol that remained in the lumen of each gastrointestinal section; however, many metabolic transformations occurred. We concluded that almost all estrogens absorbed were metabolized during the absorption process. The liver was active only in the metabolism of estrogens that escaped conjugation in the intestinal mucosa.

¹ Journal Paper No. 7384, Agr. Exp. Sta., Purdue Univ., West Lafayette, IN.

² Research supported by DHEW/Public Health Service, FDA, Contract 74-136.

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

⁴ Current address: Southern Research Institute, Birmingham, AL 35205.

⁵ Current address: Univ. of Michigan, Ann Arbor.

⁶ Dept. of Vet. Physiol. & Pharmacol., Purdue Univ.