Abstract
Objective Glucose-dependent insulinotropic polypeptide (GIP) is speculated to worsen growth hormone (GH) hypersecretion in acromegaly and to be a cause of paradoxical increases in GH (PI-GH) during 75-g oral glucose tolerance testing (75-g OGTT). Dipeptidyl peptidase-4 inhibitors (DPP4is), which increase the circulating concentration of active GIP, are frequently administered to diabetic patients, including those with acromegaly. We aimed to determine whether or not the administration of a DPP4i increases GH concentration, especially in patients demonstrating PI-GH during a DPP4i-OGTT, in which a DPP4i was administered immediately before 75-g OGTT. Methods This prospective cross-sectional study was carried out on acromegalic patients admitted to Hokkaido University hospital between June 2011 and May 2018. The participants underwent both 75-g OGTT and DPP4i-OGTT. For those who underwent surgery, immunohistochemical staining and quantitative polymerase chain reaction (PCR) for the GIP receptor (GIPR) were performed on the resected pituitary adenomas. Results Twenty-five percent of the participants had PI-GH confirmed (3 of 12 cases). Two of the three participants who demonstrated PI-GH exhibited higher circulating GH concentrations during DPP4i-OGTT than during OGTT. The increase in plasma glucose was reduced during DPP4i-OGTT compared to during 75-g OGTT, suggesting that the increase in GH during DPP4i-OGTT was due not to high glucose concentrations but instead increased GIP caused by the administration of DPP4i. The adenoma from one participant with PI-GH displayed positive immunostaining for GIPR and a higher GIPR messenger ribonucleic acid (mRNA) expression than the others. Conclusion DPP4i may enhance the GH secretion response during glucose loading, especially in individuals with PI-GH.