Mode of Action of Glucagon Revisited

It has long been accepted that glucagon action is linked to a unique pathway, the stimulation of adenylyl cyclase activity and cyclic AMP synthesis, initiated by the binding of glucagon to its receptor (Fig. 1). However, this view has been disputed and there is now evidence that the physiological effects of glucagon may occur through other mechanisms namely: (a) actions mediated through the glucagon receptor, but relying on transduction signals other than adenylyl cyclase activation and (b) effects of glucagon, secondary to the processing of the hormone into its carboxy-terminal fragment (19–29).