Reduced GLP-1 and insulin responses and glucose intolerance after gastric glucose in GRP receptor-deleted mice

By applying a newly developed ELISA technique for determining biologically active intact glucagon-like peptide [GLP-1, GLP-1-(7-36) amide] in mouse, p lasma baseline GLP-1 in normal NMRI mice was found to be normally distribut ed (4.5 +/- 0.3 pmol/l; n = 72). In anesthetized mice, gastric glucose (50 or 150 mg) increased plasma GLP-1 levels two- to threefold (P < 0.01). The simultaneous increase in plasma insulin correlated to the 10-min GLP-1 leve ls (r = 0.36, P < 0.001; n = 12). C57BL/6J mice deleted of the gastrin-rele asing peptide (GRP) receptor by genetic targeting had impaired glucose tole rance (P = 0.030) and reduced early (10 min) insulin response (P = 0.044) t o gastric glucose compared with wildtype controls. Also, the GLP-1 response to gastric glucose was significantly lower in the GRP receptor-deleted mic e than in the controls (P = 0.045). In conclusion, this study has shown tha t 1) plasma levels of intact GLP-1 increase dose dependently on gastric glu cose challenge in correlation with increased insulin levels in mice, and 2) intact GRP receptors are required for normal GLP-1 and insulin responses a nd glucose tolerance after gastric glucose in mice.