Potentiation of secretin stimulation of the pancreas.

1. In fasted anaesthetized cats which were secreting pancreatic juice at a steady slow rate in response to continuous intravenous infusion of secretin, stimulation of the dorsal vagus trunk increased the rate of secretion, the rate of output of amylase and the concentration of bicarbonate in the juice.2. The increase in rate of secretion and in concentration of bicarbonate was reduced but not abolished by atropine. It was unaffected by adrenergic blocking agents, but abolished by hexamethonium.3. No increase in rate of secretion of secretin-stimulated juice was observed on cervical stimulation of vagus nerves in which the efferent fibres had degenerated after supra-nodose section of the nerves. It is concluded that the increase in secretion rate is mediated by ;atropine-resistant' efferent vagal fibres.4. Pancreozymin, antral extracts and histamine increased the rate of secretion of secretin-stimulated juice. Pancreozymin and antral extracts also increased the rate of amylase output. These effects of pancreozymin and antral extracts were not abolished by atropine or hexamethonium.5. As vagal stimulation pancreozymin, antral extracts and histamine have little or no effect on the resting pancreas of the anaesthetized cat, it is concluded that they exert a potentiating effect on secretin. It is suggested that the mechanism of this potentiation is an increase in pancreatic blood flow, which facilitates the supply of secretin to the gland.