The secretory and vascular response to nervous and hormonal stimulation in the pancreas of the pig

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Abstract
1. The atropine-resistant action of the vagus nerves on the flow of pancreatic juice in the pig has been examined and related to certain properties of the pancreas in this species. 2. The pancreas was more sensitive to secretin in the pig than in the dog, although similar maximal rates of secretion were observed in both species. 3. The potentiation by secretin of the effects of parasympathetic stimulation on the flow of juice was conspicuous in the pig because of the heightened sensitivity to secretin and the resistance to atropine of this action of the secretory nerves. 4. Stimulation of the vagus nerves increased the output of amylase in pancreatic juice more readily than injections of pancreozymin in the pig. In the dog pancreozymin was more effective than stimulation and could alone raise the amylase output to values comparable with those attained by stimulation in the pig. In both species atropine reduced the response to pancreozymin by only 20–25%, compared with 70–95% for vagal stimulation. 5. Stimulation of the vagus nerves caused an intense, well maintained vasodilatation in the pancreas, which appeared after a shorter latent period than the secretion and was not diminished by atropine. Pancreozymin caused a smaller, and secretin only a slight, increase in pancreatic blood flow, which was also resistant to atropine, but appeared at the same time as the enhanced flow of juice. Injections of acetylcholine caused a vasodilatation which preceded the secretion but was abolished by atropine. The possibility that the pancreas receives an atropine-resistant parasympathetic vasodilator nerve supply is discussed. 6. The results provide no evidence that a substance with specific secretin-like properties might be released within the pancreas to act as a secondary transmitter for the effect of stimulation of the vagus nerves on the flow of pancreatic juice. 7. The experiments indicate that differences in the parasympathetic innervation of the exocrine cells of the pancreas between the pig and dog may underlie the observed differences in the secretory responses of the gland in these species.