Characterization of a Heat Stable,12,000 Da,Glucagon-like Immunoreactive (GLI) Peptide from Porcine Ileum That Stimulates Hepatic Glucose Production in Vivo and in Vitro 1

Abstract

Glucagon-like immunoreactivity (GLI) was extracted from porcine ileal mucosa with boiling 2 M HAc followed by elution on DEAE A-50 and fractionation on Sephadex G-50 F. Intact GLI was isolated from mesenteric blood by fractionation of several plasma samples from a mesenteric vein of a dog on Sephadex G-50 M followed by refractionation of the pooled GLI from these columns on G-50 F. Analysis of the semipurified mucosal and plasma GLI on Sephadex (3-50 SF. eluted with 0.1 M Tris/HCl + 8 M urea, pH 7.5. demonstrated a single, sharp peak of GLI with a relative molecular mass (M _r) between 12,000 and 13,000. Electrophoresis on PAGE gels at acid pH with 2 M urea demonstrated a single charged GLI species in both the plasma and mucosal fractions. Stimulation of the release of GLI from a loop of ileum isolated in situ in an anesthetized dog following removal of the known sources of glucagon (stomach, pancreas, and duodenum) resulted in an immediate and sustained increase in hepatic glucose production. The isolated GLI from ileal mucosa (5 × 10⁻⁸ M) stimulated gluconeogenesis from 10 mM [¹⁴C]alanine in hepatocytes isolated from fed rats. The stimulation was equal to 25% of the maximal stimulation observed with 10⁻⁸ M glucagon. These experiments demonstrate that the ileum synthesizes and secretes a GLI peptide with a M _r of approximately 12,000 that stimulates hepatic glucose production in vivo and in vitro.