Amines and the rat exocrine pancreas: (3) Effects of amines on pancreatic secretion

Effects of L-dopa, L-5HTP, a few amines, and related compounds on the pancreatic rate of flow, protein secretion, and bicarbonate secretion were studied in conscious rats. Single injections of L-dopa, DA and apomorphine did not modify the rate of flow, while an increase was seen with infusion of DA. L-dopa stimulated the protein secretion. L-5HTP and 5-HT decreased the rate of flow and protein secretion. Effects of L-dopa and L-5HTP on the protein secretion were prevented by DA- and 5-HT blockers, respectively. Neither L-dopa nor L-5HTP had any effect on the bicarbonate secretion. Secretin and cholinergic agents (acetylcholine and carbamylcholine) strongly stimulated the rate of flow of pancreatic juice. alpha-Agonists (phenylephrine and clonidine) decreased the rate of flow, and the effects were inhibited by an alpha-blocker. The alpha-agonists had no effect on protein secretion. Although, alpha-blockers (phenoxybenzamine and phentolamine) had no effects on the rate of flow, they did decrease the protein secretion. Isoproterenol was a potent secretagogue, and the effect was suppressed by a beta-blocker. Histamine had no effect on the rate of flow. The results were discussed in relation to our previous histochemical and chemical findings, and the species difference between rats and dogs in response to the amines.