The hypothesis that PGE 2 mediates the effect of pentagastrin on jejunal Na-K-ATPase and adenylate cyclase activities was tested in rats. Mucosal PGE 2 and cAMP contents, Na-K-ATPase and adenylate cyclase activities were determined 45 min after IV pentagastrin (1 μg/100 g b.w.) administration to pyloric ligated rats. Pentagastrin almost doubled mucosal PGE 2 content as compared to that in saline-treated rats: 198 ± 19 (S.E., N = 1) and 109 ± 9 (S.E., N = 26) pg/mg tissue, respectively, inhibited mucosal Na-K-ATPase activity: 16.4 ± 0.7 (S.E., N = 8) as compared to 26.7 ± 4.0 (S.E., N = 13) μmole/mg protein/h in saline-treated rats, stimulated adenylate cyclase activity by 146% and increased mucosal cAMP content by 80%. Pretreatment with indomethacin (4 mg/kg b.w., s.c./day X 2) prevented the increase in PGE 2 content, the stimulation of adenylate cyclase activity and the inhibition of jejunal Na-K-ATPase activity induced by pentagastrin. The results reported thus suggest that the mechanisms whereby pentagastrin affects intestinal water and electrolyte transport are probably mediated by mucosal PGE 2 and include inhibiton of Na-K-ATPase activity and stimulation of the adenylate cyclase - cAMP system.