Metabolism of `251-labelled trypsin in man: evidence for recirculation

251-labelled human trypsin metabolism has been investigated in man. Three subjects received 1251-trypsin and 1311-albumin intravenously. Against a background secretin infusion (lu/kg/h), trypsin decayed biexponentially from the serum with half-lives of 17.5, 21, and 24 minutes for the rapid disappearance phase and 520, 540, and 560 minutes for the slow phase. Between 130% and 38% of the 1251 injected was recovered from duodenal juice aspirated continuously over 300 minutes. In contrast, less than 1 % of the '311-albumin injected was recovered. When bile and pure pancreatic juice were collected at endoscopic retrograde cholangiopancreatography after intravenous 12511_ trypsin in a fourth subject 125j radioactivity was found to be secreted v,ia both these routes. After 1251-trypsin infusion into the duodenum 11 % of the total dose was found to be present in the circulation after 75 minutes. These results support the concept that recirculation of trypsin exists in man.