Anti-inflammatory and antinociceptive activities of glucagon-like peptides: evaluation of their actions on serotonergic, nitrergic, and opioidergic systems.

Rationale: Glucagon-like peptide-1 (GLP-1) and glucagon-like peptide-2 (GLP-2) are gut derived hormones. GLP-1 and GLP-2 were shown to have pleiotropic effects in intestinal and pancreatic diseases.

Objective: We aimed to investigate the activities of GLP-1 and GLP-2 on nociception and inflammation in mice, involving their actions on serotonergic, nitrergic, and opioidergic systems.

Methods: Antinociceptive and anti-inflammatory activities of intraperitoneally injected GLPs were evaluated in hotplate latency test, formalin-induced behavioral, and paw edema tests. Ondansetron, a selective 5-HT receptor antagonist; L-NAME, a NOS inhibitor; and naloxone, an opioid antagonist were injected to determine the mechanisms of antinociception and anti-inflammation. We also measured blood glucose levels and performed rotarod test in order to evaluate whether the hypoglycemic effect of GLP compounds or alterations in locomotor activity may affect the latency in hotplate test and activity in formalin test.

Results: GLP-1 (0.2 mg/kg) and GLP-2 (0.05, 0.2 mg/kg) significantly increased pain threshold. GLP-1 (0.2 mg/kg) and GLP-2 (0.05, 0.1, 0.2 mg/kg) significantly decreased formalin-induced licking and shaking behaviors. GLP-1 or GLP-2 showed no significant inhibitory action on formalin-induced swelling in paws of mice. Antinociceptive actions of GLP-1 and GLP-2 were significantly decreased with ondansetron and naloxone, and paw shaking behavior significantly increased with naloxone. GLP-1 and GLP-2 did not impair rotarod performance, and did not cause a significant hypoglycemic effect in our normoglycemic mice after rotarod test.

Conclusion: These finding indicated that the antinociceptive and anti-inflammatory effect of GLP-1 was related to opioidergic system. Antinociceptive effect of GLP-2 was partially related to 5-HT3 serotonergic or opioidergic system in hotplate test. However, the anti-inflammatory effect of GLP-2 was not directly related to 5-HT3, NO or opioids.