Stimulatory effect of monitor peptide and human pancreatic secretory trypsin inhibitor on pancreatic secretion and cholecystokinin release in conscious rats.

The stimulatory effects of monitor peptide (MP) that was recently purified from rat bile-pancreatic juice on cholecystokinin (CCK) release and pancreatic exocrine secretions were examined in the conscious rat. As the sequence of MP has some homology with human pancreatic secretory trypsin inhibitor (hPSTI), the effects of these two materials were compared with each other. Rats were prepared with external bile and pancreatic fistulae. Pancreatic juice diversion significantly increased pancreatic secretions, but the intraduodenal injection of MP (0.9 micrograms per rat) could further increase pancreatic secretions. The MP injection produced significantly higher plasma CCK concentrations than the injection of isotonic saline solution did. Trasylol was infused simultaneously with pancreatic juice diversion to completely eliminate residual luminal protease activities. The MP (0.9 micrograms per rat) still showed the stimulatory effect, but hPSTI did not show any stimulatory effect on pancreatic secretion. Plasma CCK concentrations produced by MP were significantly higher than those produced by hPSTI. It was concluded that MP has a strong species specificity and that MP could stimulate CCK release and pancreatic exocrine secretions, not only via inhibiting luminal protease activities but also probably with a direct effect.