Role of glucagon in regulation of glucose production in exercising dogs

Publisher Website
Google Scholar
Abstract
Insulin is an essential regulator of glucose production (Ra) and utilization during exercise, but the role of glucagon remained to be clarified. Eleven dogs ran on a treadmill for 3 h. Within the 1st h, exercise doubled plasma immunoreactive glucagon (IRG), Ra, and lactate, while insulin (IRI) decreased. Somatostatin (ST) infused in the 2nd h lowered IRG below basal levels and IRI decreased further. Plasma glucose declined because Ra fell more rapidly than glucose metabolic clearance (MCR). Lactate was further increased. Cessation of ST caused a rebound in IRG, IRI, Ra, MCR and glucose. When glucagon was infused (6 ng/kg .cntdot. min) with ST, IRG rose above basal, while IRI remained suppressed; the suppression of Ra, plasma glucose and MCR was corrected. When exercise and ST started concurrently, both IRG and IRI decreased. Plasma glucose fell because the exercise-induced Ra increment was suppressed by 75%. MCR at 1st rose and then declined, and the rise of FFA was accelerated. IRG/IRI ratio was directly correlated to RA. Glucagon plays a direct role in initiating and maintaining elevated glucose production and an indirect role in control of glucose uptake during exercise. Hypolglycemia occurring during suppression of IRG and Ra can increase the adrenergic drive, thereby causing increased lipolysis and muscle glycogenolysis, thus decreasing muscular glucose uptake.