Kinetics of insulin secretion and glucose intolerance in adult patients with cystic fibrosis.

Disturbance of glucose metabolism and diabetes is an increasing complication in adult patients with cystic fibrosis (CF). The aim of the present study was to evaluate the impact of insulin and glucagon-like peptide-1 (GLP-1) secretion on early disturbance of glucose metabolism and clinical status in an unselected cohort of CF patients. 34 adult CF patients and 10 matched healthy subjects underwent an oral glucose tolerance test. Blood samples were taken to measure indices for insulin secretion and insulin sensitivity. Metabolic parameters were correlated with anthropometric and clinical data. In CF patients, there was a decrease in first phase insulin secretion (FPIR) with progressive delay of insulin peak, which was correlated with worsening glucose tolerance (Stumvoll index: normal glucose tolerance: 450±291; impaired fasting glucose: 252±203; impaired glucose tolerance: 309±254; CF related diabetes: 18±41; controls: 950±388) and high early post-challenge glucose peak (p<0.01 vs. controls). However, total insulin secretory capacity was not decreased in CF patients resulting to low glucose levels in the late phase (120-180 min). We found neither a difference in basal or maximal GLP-1 levels nor in insulin resistance between study groups. Maximum glucose levels correlated with impaired FEV1 (rs=-0.5, p=0.002). Our data demonstrate that alteration of FPIR, but not insulinopenia, insulin resistance, or disturbed GLP-1 secretion is present in the prediabetic state in CF patients. Correlation between high glucose levels and worse clinical status suggest that diabetes treatment should be initiated more early in the state of glucose intolerance.