Opposing central and peripheral actions of brain-gut peptides: a basis for regulation of gastric function

The existence of an increasing number of peptides in both the gut and the brain provides the basis for the concept of a brain-gut axis. However, to date, no unifying hypothesis has been put forward to explain the physiologic significance of this remarkable phenomenon. The present study examines the central and peripheral actions on gastric function of cholecystokinin octapeptide (CCK-8), somatostatin, and bombesin, all of which exist in both the gut and brain. Intravenous infusion of CCK-8, in doses of 50, 100, and 200 pmol X kg-1 X hr-1, caused 28%, 38%, and 52% inhibition, respectively, of the rate of gastric emptying of a liquid meal in dogs. By contrast, the injection of 32, 64, and 128 pmol X kg-1 into the lateral cerebral ventricle of these dogs accelerated gastric emptying by 6%, 26%, and 32%, respectively. Bombesin, which stimulated gastric acid secretion in a dose-dependent manner but which had no effect on the submaximal acid response to pentagastrin when administered peripherally, inhibited in a dose-dependent manner the submaximal response to pentagastrin when given centrally, with a maximal inhibition of 66% +/- 5%, at a dose of bombesin of 180 pmol X kg-1. Similarly, somatostatin-14 caused graded inhibition of pentagastrin-stimulated acid secretion when it was administered peripherally but caused dose-dependent augmentation of the acid response when it was given centrally. Maximal inhibition of 51% of the pentagastrin response occurred with a peripheral dose of somatostatin of 800 pmol X kg-1 X hr-1. By contrast, maximal augmentation of the pentagastrin response of 78% occurred when a dose of 400 pmol X kg-1 of the peptide was injected into the lateral ventricle. We conclude that CCK-8, bombesin, and somatostatin have opposing actions on gastric function when administered centrally and peripherally. We propose that this phenomenon may be common to all neuropeptides of the brain-gut axis and may provide a basis for central regulation of gut function.