Several studies have pointed to a neural regulation of glucose dependent insulinotropic peptide (GIP) secretion. Bombesin is a neuropeptide found in the amphibian brain and gastrointestinal system homologous to the C terminus of gastrin-releasing protein (GRP) in mammalians, which displays a wide range of metabolic actions.
Aim: Aim of this study was to investigate the effect of intracerebroventicular infusion of bombesin in a centrally mediated regulation of GIP secretion in dogs.
Methods: Twenty-four adult dogs were used in this study. In group 1, the animals received a bolus or a continuous i.c.v. infusion over a 3-hour period of bombesin or an equivalent amount of artificial cerebrospinal fluid (aCSF). In group 2, the continuous infusion was repeated with a simultaneous intraduodenal infusion of a glucose load. Blood samples were taken from cannulation of a hind limb vein and plasma levels of glucose, insulin and GIP were assayed.
Results: Bolus i.c.v. infusion of bombesin evoked a strong clinical reaction in the animals, which had all the characteristics of sympathetic stimulation. The levels of glucose and GIP demonstrated a significant increase without however, a respective increase in plasma insulin levels in both bolus and continuous i.c.v. infusions. In the combined experiment there was a significant increase in all parameters.
Conclusions: Intracerebroventricular administration of bombesin increases GIP secretion in a nutrient independent manner, while inhibiting GIP and glucose induced insulin secretion. However in the presence of intraduodenal glucose load insulin secretion escapes bombesins inhibitory effect, demonstrating an alternative regulation of the entero-insular axis, which is influenced by neural or neurohormonal mediators.