Department of Medical Anatomy, Section B, The Panum Institute, University of Copenhagen, Blegdamsvej 3, 2200 N, Copenhagen, Denmark. J.Thulesen@mai.ku.dk
The therapeutic potential of the intestinotrophic mediator glucagon-like peptide-2 (1-33) [GLP-2 (1-33)] has increased interest in the pharmacokinetics of the peptide. This study was undertaken to investigate whether the primary degradation product GLP-2 (3-33) interacts with the GLP-2 receptor. Functional (cAMP) and binding in vitro studies were carried out in cells expressing the transfected human GLP-2 receptor. Furthermore, a biologic response of GLP-2 (3-33) was tested in vivo. Mice were allocated to groups treated for 10 days (twice daily) with: (1) 5 microg GLP-2 (1-33), (2) 25 microg GLP-2 (3-33), (3) 5 microg GLP-2 (1-33)+100 microg GLP-2 (3-33), or (4) 5 microg GLP-2 (1-33)+500 microg GLP-2 (3-33). The intestine was investigated for growth changes. GLP-2 (3-33) bound to the GLP-2 receptor with a binding affinity of 7.5% of that of GLP-2 (1-33). cAMP accumulation was stimulated with an efficacy of 15% and a potency more than two orders of magnitude lower than that of GLP-2 (1-33). Increasing doses of GLP-2 (3-33) (10(-7)-10(-5) M) caused a shift to the right in the dose-response curve of GLP-2 (1-33). Treatment of mice with either GLP-2 (1-33) or (3-33) induced significant growth responses in both the small and large intestines, but the response induced by GLP-2 (3-33) was much smaller. Co-administration of 500 microg of GLP-2 (3-33) and 5 microg GLP-2 (1-33) resulted in a growth response that was smaller than that of 5 microg GLP-2 (1-33) alone. Consistent with the observed in vivo activities, our functional studies and binding data indicate that GLP-2 (3-33) acts as a partial agonist with potential competitive antagonistic properties on the GLP-2 receptor.