Fate of intraduodenally administered somatostatin in rats in vivo

Intraduodenally administered somatostatin-14 (a milk-borne peptide) has been shown to influence the pancreatic secretions in rats and dogs. To delineate the mechanism involved in the intraduodenal somatostatin-14, the fate of intraduodenal somatostatin-14 was investigated by administering [¹²⁵I][Tyr¹¹]somatostatin-14 ([¹²⁵I][Tyr¹¹]SS14) into the lumen of isolated duodenum in vivo of suckling and adult rats. At 2, 5, 10, and 30 min after administration, the radioactivity in the duodenal contents, duodenal wall, blood, liver, and kidney was measured, and the extracted radioactivity was analyzed for intact [¹²⁵I][Tyr¹¹]SS14 by reversed-phase high performance liquid chromatography. Radioactivity disappeared rapidly from the duodenal lumen with 50% of loss occurring at 2 min. No trace of intact [¹²⁵I][Tyr¹¹]SS14 was detected in any of the samples, except duodenal contents of suckling rats at 2 min, suggesting a rapid metabolism of SS14 in the duodenal lumen and a lack of duodenal absorption of intact SS14 in the rat.