Diversion of pancreatic-biliary (PB) secretions in rats for 23 days led to loss of enterokinase (EK) activity in bypassed segments of the small intestine. Simultaneous oral trypsinogen and bile salt (TB) supplements prevented the loss of EK activity. To study the temporal course of events after PB diversion and to determine if the loss of EK is reversible, PB diversion was performed in rats by surgical transposition of the 4-cm segment of duodenum including the ampulla of Vater to a point 30 cm distal to its original site. Bypassed and control (sham- and nonoperated) rats fed standard rat chow were sacrificed at 10, 23, and 45 days after surgery. One bypassed group was fed standard chow for 23 days and then chow supplemented with TB until sacrifice at 45 days. At sacrifice, the intestines were divided into segment 1 (the bypassed proximal 30 cm) and segment 2 (the 30 cm distal to the bypass). In segment 1, EK disappeared almost completely by 10 days and remained at the same low levels at both 23 and 45 days (p less than 0.05). No significant changes in EK levels were found at any time in segment 2 distal to the bypass. Mucosal disaccharidase activity in segment 1 increased or showed no change. In rats with delayed TB supplementation, EK activity in segment 1 returned almost to control levels at the time of sacrifice. The results confirm the importance of PB secretions in the maintenance of EK activity. The effects of bypass on EK are both enzyme- and site-specific.(ABSTRACT TRUNCATED AT 250 WORDS)