Résumé : In order to characterize the mode of action of pancreatic hormones, the authors measured intratissular levels of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) in rat pancreas, submitted in vitro and in vivo to stimulation of various hormones. In vitro effects of cholecystokinin (CCK) caerulein, pentagastrin, carbamylcholine, sodium fluoride, secretin, vasoactive intestinal polypeptide (VIP) and glucagon were measured in presence and absence of 10 mM theophylline. In vivo effects were tested at various time intervals, from 30 sec to 50 min, following intraperitoneal injection of pilocarpine and intravenous injection of CCK secretin and VIP. cAMP was measured according to Gilman and cGMP with a modification of the method of Steiner et al. The results are as follows: Hormones and hormone analogs favoring secretion of hydrolases did not affect intrapancreatic levels of cAMP, even in presence of 10 mM theophylline. Secretin rapidly elevated levels of cAMP, and by as much as 500% at a 1.10-7 M concentration, in presence of 10 mM theophylline. VIP reproduced the effect of secretin, but was 10 times less efficient, on a molar basis. Glucagon was without effect. Preliminary results indicate a slight decrease in levels of intratissular cGMP in pancreatic fragments incubated in vitro in presence of CCK carbamylcholine or pentagastrin. In vivo, however, an increase (+80%) in cGMP levels was observed during the 3 min interval following injection of pilocarpine. Secretin did not affect the levels of cGMP. In conclusion: These results give further support to the role of cAMP as an intracellular mediator of secretin. They suggest a biochemical relationship between VIP and secretin. They also indicate that cGMP might play an important role in the action of hormones and neurohormones favoring secretion of pancreatic hydrolases.