The role of extracellular Ca2+ and cyclic nucleotides in the mechanism of enzyme secretion from the cat pancreas.

The role of Ca2+ in protein secretion from the isolated perfused cat's pancreas, the effect of the dibutyryl analogues of cAMP and cGMP, and the interrelation of Ca2+ and the nucleotides were studied. The following results were obtained: 1. Pancreatic enzyme secretion can be elicited by CaCl2 injections into the pancreatic arteries and is linearily related to the peak Ca2+ concentration in the effluent perfusate. Different background Ca2+ concentrations in the perfusate (3 mM or 0.125 mM) do not disturb this relation, indicating that no adaptation occurs. The effect of Ca2+ injections is of the same magnitude as that evoked by the hormones pancreozymin or acetylcholine. 2. Injections of Ca2+ potentiate the effects of dibutyryl adenosine 3',5'-cyclic monophosphate (dbcAMP), dibutyryl guanosine 3',5'-cyclic monophosphate (dbcGMP) or theophylline. 3. Infusion of low doses of pancreozymin increases the Ca2+ effect. The findings indicate that extracellular Ca2+ is involved in the mechanism of enzyme secretion and that Ca2+ and cyclic nucleotides have a synergistic action on the target.