GCG and type 2 diabetes mellitus: Studies involving clamp technique, which keeps glucose constant and thus allows for the effects of changes in glucose levels on glucagon secretion to be readily isolated, showed that administrations of insulin suppressed glucagon secretion in healthy humans (Raskin et al., 1975), and patients with type 1 (Raskin et al., 1976) or type 2 diabetes (Greenbaum et al., 1991; Hamaguchi et al., 1991).