Features of carbohydrate metabolism and incretin secretion in patients with Cushing disease and acromegaly

Abstract

Aim. This study aims to analyse the rhythm and levels of incretins and neuropeptides secretion in patients with Cushing disease (CD) and acromegaly, and thus specify the pathogenesis of carbohydrate metabolism disturbances. Matherials and methods. In this study, 42 patients (mean age, 37.5 years) with CD and acromegaly were enrolled. All patients were newly diagnosed with CD and acromegaly, and none had a history of previous drug therapy, radiotherapy or pituitary surgery. All patients underwent OGTT, during which glucose, glucagon, GLP-1, GLP-2, GIP and ghrelin were evaluated at 0, 30 and 120 min, respectively. Results. During OGTT, glucose levels were not significantly different between the groups. The relevance of pre-diabetes was higher in patients with CD. In these patients, while glucagon levels were substantially higher at all cut-off points than those in controls (р = 0.001), GIP secretion was slightly lower. The acromegaly group was characterised by an inverse rhythm of GIP secretion with no peak level at 30 min. In addition, GLP-1 levels were significantly higher in patients with CD (р = 0.047). Similarly, GLP-2 levels were also significantly higher in patients with CD than in those with acromegaly and controls (p = 0.001). Finally, ghrelin levels were significantly higher in patients with CD (р = 0.013) and acromegaly (р = 0.023). Conclusion. More pleiotropic actions of glucocorticoids can explain the higher relevance of carbohydrate metabolism disturbances in patients with CD. This can also be explained by higher levels of glucagon secretion, which do not depend on the type of carbohydrate metabolism disorder and are stimulated by a direct action of glucocorticoids on the glucagon receptor. GIP and GLP-1 secretion in patients with CD and acromegaly are characterised by the inverse rhythm with no peak levels, implying that these hormones do not play a crucial role in the development of carbohydrate disturbances in these patients. In contrast, GLP-2 and ghrelin seem to influence and potentially regulate glucose homeostasis in patients with CD and acromegaly.