ASSESSMENT OF RESIDUAL INSULIN-SECRETION IN DIABETIC-PATIENTS USING THE INTRAVENOUS GLUCAGON STIMULATORY TEST - METHODOLOGICAL ASPECTS AND CLINICAL-APPLICATIONS

Defective insulin secretion plays a crucial role in insulin-dependent (Type 1) and non-insulin-dependent (Type 2) diabetes mellitus as well as in many secondary farms of the disease. Glucagon is a potent stimul us for the islet beta-cell, and intravenous bolus injection of 1 mg gl ucagon has been widely used to assess endogenous insulin secretion for clinical or research purposes. Plasma C-peptide levels (less commonly insulin) are usually measured immediately before and 6 min after gluc agon injection. The C-peptide response to glucagon is well-correlated with the beta-cell response to mixed meals or other stimuli commonly u sed to characterize endogenous insulin secretion (oral or intravenous glucose, standard meals, arginine, etc.) and has the advantage of shor ter duration and simple standardization. The glucagon test shows good intra-subject reproducibility, although in diabetic patients it may be influenced by variable prevailing blood glucose levels. Several appli cations of the glucagon test have been developed. In Type 1 diabetes, the glucagon test has been used to discriminate between patients with and without residual insulin secretion. This can he especially importa nt during the first few months, or even years, following initiation of insulin therapy when attempts to stop the immunological destruction o f the beta-cell are made. Assessment of endogenous insulin secretion i s also important after pancreas or islet transplantation. In patients with Type 2 diabetes mellitus, in which residual endogenous insulin se cretion is common, characterization of the disease may help in the cho ice of therapy for the individual patient (insulin, sulphonylureas or combined therapy). Thus, the glucagon lest is a simple, reliable and u seful tool for clinical evaluation of diabetes mellitus.