Neuropeptide regulation of feeding in dogs

Norepinephrine and four families of neuropeptides, namely, neuropeptide Y (NPY), opioid peptides, galanin, and growth hormone-releasing factor (GRH), have been shown to stimulate feeding after central administration. Because these studies were mainly done on laboratory rats, the present study was designed to ascertain the central stimulators of feeding in dogs. We have shown that porcine and human pancreatic polypeptides (PPs), when administered into the third cerebral ventricle (intracerebroventricularly), increased food and water intake of satiated animals but that the COOH-terminal fragments [hPP-(18-36) and hPP-(23-36)] did not do so at the same molar dose (11.9 nmol). The kappa-opioid receptor agonist dynorphin (A-(1-17) also stimulated food and water intake, whereas alpha-neoendorphin and Met-enkephalin did not. These results suggest the structural specificity of PPs and dynorphin peptides for stimulating feeding. Surprisingly, neither intracerebroventricular injections of NPY and peptide YY nor intracerebroventricular pretreatment with anti-hNPY gamma-globulin modulated feeding, stressing the species differences in the feeding response to exogenous substances and the underlying physiology. Intracerebroventricular injections of norepinephrine, GRH, galanin, and pancreastatin also failed to increase food intake, although most substances tended to or did increase water intake. These results suggest that neuropeptides play a role in a species-specific way in modulating appetite regulation.