Vagal efferent nerve-dependent inhibitory action of pancreatic polypeptide and peptide YY in conscious rats: comparison with somatostatin.

The release of pancreatic polypeptide (PP) and peptide YY (PYY) is regulated by the vagal nerve, and the inhibitory effect of these peptides on pancreatic exocrine secretion shows indirectly via a neural mechanism. To determine the role of the vagal nerve on the inhibitory action of these peptides on the pancreas, we compared the effect on the pancreatic response to bile and pancreatic juice diversion in conscious rats with and without vagotomy. We also studied this response in rats treated with capsaicin, because bile-pancreatic juice diversion is the most potent endogenous stimulation of pancreatic secretion in conscious rats. In addition, since somatostatin potently inhibits of pancreatic enzyme secretion, the effects of PP and PYY were compared with somatostatin. An intravenous infusion of 2.5 nmol/kg per h of PP and PYY significantly inhibited the pancreatic responses of bile and pancreatic juice diversion in animals with an intact vagal nerve and in those treated with capsaicin, whereas the same dose of peptides failed to inhibit pancreatic secretion in vagotomized rats. Somatostatin inhibited pancreatic secretion under all conditions tested. We concluded that the inhibitory action of PP and PYY on pancreatic secretion is fully mediated by the vagal efferent nerve although other multiple mechanisms are involved for the inhibitory action of somatostatin.