Responses of plasma adenosine 3′, 5′-monophosphate, blood glucose and plasma insulin to glucagon in humans

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Abstract
The effect of glucagon on plasma cyclic AMP (CAMP), insulin and blood glucose was examined in normal adult subjects. After an i.v. injection of glucagon there was a rapid, dose-dependent increase of plasma cAMP as well as insulin and blood glucose. Multiple injections of glucagon to the same subject with 60 min intervals gave almost identical responses of plasma cAMP and blood glucose, whereas the insulin response tended to decrease with time. Dose-dependent increases of plasma CAMP, insulin and blood glucose were also seen during a continuous i.v. infusion of glucagon. With the lowest doses of glucagon the blood glucose and plasma insulin concentrations were increased without any change of plasma CAMP. Plasma CAMP, insulin and blood glucose declined prior to the termination of glucagon infusion. During an endogenous hyper-glucagonaemia, induced by alanine injection, there was no discernible change of plasma CAMP. We conclude that the early events of glucagon action may be studied in vivo by monitoring plasma CAMP. However, variations of plasma glucagon within the physiological range are not accompanied by measurable changes of cAMP in the peripheral circulation.