Background: Increased plasma levels of calcitonin gene-related peptide-I (CGRP-I) and procalcitonin (Pro-CT) (both also named calcitonin peptides (CT peptides)) are associated with obesity and systemic inflammation. Glucose-dependent insulinotropic polypeptide (GIP), a nutrient-dependent incretin hormone, was recently found to induce CGRP-I and CT expression in human adipocytes in vitro. However, a physiological relevance of a possible interaction between GIP and CT peptides has not yet been studied.
Methods: In this study, we analyzed the effect of GIP on the expression of CGRP-I and CT mRNA in human subcutaneous adipose tissue within a randomized, controlled trial. Seventeen male obese subjects were infused with GIP [2.0 pmol kg(-1) min(-1) for 240 min] or placebo, either in the fasting state, during euglycemic-hyperinsulinemic (EC) or hyperglycemic-hyperinsulinemic clamps (HC).
Results: The CGRP-I gene expression was detected in all investigated adipose tissue samples, whereas very low CT expression was found in only 8 out of 116 analyzed samples. No significant influence of either GIP or glucose and insulin infusions on the CGRP-I and CT expression was observed in any of the individual experiments (GIP infusion, EC and HC) or in the combined analysis of all experiments with and without GIP. Furthermore, CGRP-I expression was not correlated with plasma GIP level before or after 240 min of infusions or clamps.
Conclusion: In contrast to in vitro data, an acute application of GIP has no effect on mRNA expression of CT peptides in subcutaneous adipose tissue of obese humans.
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