Exercise-induced fall in insulin and hepatic carbohydrate metabolism during muscular work

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Abstract
To examine the role of the exercise-induced fall in insulin, dogs were studied during 150 min of treadmill exercise alone (C) or with insulin clamped at basal levels by an intraportal infusion so as to prevent the normal fall in its concentration (IC). To counteract the suppressive effect of insulin on glucagon release, glucagon was replaced intraportally in a separate group of dogs in which insulin levels were clamped (IC + G). In all dogs, catheters were placed in an artery and in the portal and hepatic veins for sampling and in the vena cava and the portal vein for infusion purposes. Glucose production (Ra) and gluconeogenesis were assessed with isotope and arteriovenous difference techniques. In C, insulin fell 5 +/- 2 microU/ml by the end of exercise and was unchanged in IC (delta 0 +/- 2 microU/ml) and IC + G (delta 0 +/- 1 microU/ml). Glucagon rose 54 +/- 11 pg/ml with exercise in C and was unchanged in IC (delta - 4 +/- 11 pg/ml), and normal increments were restored in IC + G (delta 55 +/- 10 pg/ml). Catecholamines and cortisol rose similarly in all groups. Ra increased by an average of 4.0 +/- 0.4, 0.9 +/- 0.3, and 1.8 +/- 0.4 mg.kg-1.min-1 during exercise in C, IC, and IC + G, respectively. Gluconeogenesis from alanine rose by 212 +/- 34, 91 +/- 39, and 184 +/- 47% with exercise in C, IC, and IC + G.(ABSTRACT TRUNCATED AT 250 WORDS)