Rat and porcine galanin are equipotent in inhibiting insulin responses to glucose in the anesthetized rat.

The structure of rat galanin, recently elucidated using recombinant DNA technology, differs from porcine galanin by three amino acid residue substitutions at positions located in the C-terminal region. A synthetic replicate of the proposed structure of rat galanin was prepared and its potency to inhibit insulin responses to glucose in anesthetized rats was compared with that of porcine galanin. Within experimental error, the dose-response curves of porcine and rat galanin to inhibit glucose-stimulated rat insulin responses were indistinguishable. The ED50 dose of porcine galanin was 0.6 micrograms/100 g body weight and for rat galanin 0.8 micrograms/100 g body weight. These results suggest that the C-terminal region of the molecule is not essential for galanin's potent inhibitory action on insulin responses to glucose administration.

Inhibition of insulin release by galanin and gastrin-releasing peptide in the anaesthetized rat.

The present study was designed to determine the effects of intravenously administered galanin or gastrin-releasing peptide (GRP) on glucose- and/or glucose-dependent insulinotropic peptide (GIP)-stimulated insulin release in the anaesthetized rat. Galanin inhibited glucose-stimulated insulin responses in a dose-related manner. Galanin also inhibited insulin release in response to glucose administered with GIP; this effect was due largely to inhibition of the glucose-stimulated component since galanin did not inhibit GIP-stimulated insulin release. Galanin also inhibited insulin responses to ingestion of a mixed meal. GRP inhibited glucose-stimulated insulin responses, and the insulin responses to glucose plus GIP; unlike galanin, GRP inhibited both glucose- and GIP-stimulated insulin release. GRP also inhibited insulin release following ingestion of a mixed meal. The results suggest a possible modulatory role for these neuropeptides in regulation of insulin secretion.