Absorption and disposition of epithiosteroids in rats (2): Avoidance of first-pass metabolism of mepitiostane by lymphatic absorption.

1. Absorption of mepitiostane (MP) from the gastrointestinal tract was examined using thoracic duct-cannulated rats. 2. When 14C-MP was administered into the small intestine, 34% of the radioactivity was recovered in the 6-h thoracic duct lymph. More than 90% of this radioactivity was due to unchanged MP and most of the MP in the lymph was carried in the lipid core of the chylomicrons and VLDL. 3. Radioactivity in the portal blood was extensively extracted by the liver and excreted into bile as polar metabolites. Thus, most unchanged MP which entered the systemic circulation following oral administration was drug absorbed via the intestinal lymphatics. 4. MP avoids the first-pass effect by lymphatic adsorption.