The role of diminished beta cell reserve and insulin resistance in secondary sulfonylurea failure of type 2 diabetes mellitus.

ABSTRACT

INTRODUCTION: The correction of hyperglycemia by insulin treatment has been shown to ameliorate beta cell function and insulin sensitivity in SU failure patients, and there also appears to have disparity between tests of beta cell function among these patients. The objectives of this study were to determine beta cell secretory reserve and insulin resistance of secondary SU failure type 2 diabetic patients who had fairly good glycemic control compared with those who were SU responsive and the disparity of beta cell responses to glucose and non-glucose stimuli were examined in these two groups. SUBJECTS AND METHOD: Eight secondary SU failure, insulin-treated and 11 SU responsive type 2 diabetic patients who were matched for age, degree of obesity, duration of diabetes as well as HbAlc were studied. Intravenous glucagon and oral glucose tolerance tests (OGTT) as well as short intravenous insulin tolerance test using arterialized venous blood were randomly performed on separate occasions to assess beta cell secretory reserve and insulin sensitivity, respectively. RESULTS: Basal (0.37+/-0.05 (SEM) vs 0.80+/-0.14 nmol/l; p=0.02) and stimulated c-peptide levels (0.66+0.08 vs 1.16+/-0.14 nmol/l; p=0.007) after glucagon as well as basal (0.46+/-0.06 vs 0.73+/-0.10 nmol/l; p=0.046) and maximal c-peptide responses (1.41+/-0.14 vs 1.97+/-0.14 nmol/l; p=0.021) to glucose stimulation were significantly lower in SU failure than SU responsive patients. However, the incremental changes of c-peptide over basal after glucagon (0.29+/-0.06 vs 0.37+/-0.09 nmol/l) and glucose (AUC 36.9+/-7.6 vs 47.9+/-4.5 nmol/l/h) were not different between both groups. There were strong positive relationships between basal and stimulated c-peptide responses to glucagon (r=0.818; p=0.002) and glucose (r=0.85; p=0.001) in SU responsive patients but these relationships were not as strong in SU failure patients (r=0.682; p=0.062 and r=0.41; p=NS, respectively). Insulin sensitivity did not differ between the two groups. CONCLUSION: This study demonstrated that decreased basal, but not stimulated, insulin secretion was possibly a major factor associated with secondary SU failure in type 2 diabetic patients. With comparable glycemic control, there was no disparate beta cell responses to glucose and glucagon in patients with or without secondary SU failure.