Role of changes in insulin and glucagon in glucose homeostasis in exercise.

Abstract

This experiment was performed to determine if plasma glucose homeostasis is maintained in normal human volunteers during light exercise (40% maximal oxygen consumption [VO2 Max]) when changes in insulin and glucagon are prevented. Hormonal control was achieved by the infusion of somatostatin, insulin, and glucagon. Glucose kinetics and oxidation rates were determined with stable isotopic tracers of glucose, and by indirect calorimetry. Two different rates of replacement of insulin and glucagon were used; in one group, insulin was clamped at 19.8±2.6 AU/ml (high-insulin group), and in the other group insulin was clamped at 9.2±1.3 jzU/ml (low-insulin group). Glucagon was maintained at 261±16.2 and 124±6.4 pg/ml, respectively, in the high-insulin and low-insulin groups.Without hormonal control, plasma glucose homeostasis was maintained during exercise because the increase in glucose uptake was balanced by a corresponding increase in glucose production. When changes in insulin and glucagon were prevented, plasma glucose concentration fell, particularly in the high-insulin group. Glucose uptake increased to a greater extent than when hormones were not controlled, and glucose production did not increase sufficiently to compensate. The increase in glucose uptake in the hormonal control groups was associated with an increased rate of glucose oxidation. When euglycemia was maintained by glucose infusion in the hormonal control subjects, the modest increase in glucose production that otherwise occurred was prevented.

The physiological regulation of glucose flux into musclein vivo

“…The decline in insulin secretion potentiates the actions of glucagon (Lavoie et al, 1997;Lins et al, 1983;Wasserman et al, 1989c). Studies in animals (Wasserman et al, 1984;Wasserman et al, 1985;Wasserman et al, 1989b) and humans (Hirsch et al, 1991;Lavoie et al, 1997;Wolfe et al, 1986) demonstrate that the increase in glucagon is the primary stimulator of hepatic glucose production during exercise. The powerful effect of glucagon on hepatic glucose production was recently demonstrated by Berglund et al (Berglund et al, 2009).…”

Dynamic Modeling of Exercise Effects on Plasma Glucose and Insulin Levels

“…Similar trends have been observed in human studies. 13,16 An increase in exercise intensity also amplifies glucose uptake by the working tissues. 17 In order to maintain plasma glucose homeostasis, hepatic glucose release also increases with increasing work intensity.…”

“…Data from Wolfe and colleagues 16 were used to investigate the plasma insulin dynamics during exercise, where healthy subjects performed a continuous bicycle exercise for 60 minutes (PVO 2 max = 40). Blood samples were taken at regular intervals to measure the plasma insulin level.…”

“…Data from a separate study by Ahlborg et al 20 were used to validate the insulin model (see Figure 4), where healthy subjects performed light exercise (PVO 2 max = 30) for 120 minutes, and the removal of plasma insulin from the circulatory system was observed. In the glucose model, parameters a 3 and a 4 for the G up [Equation (9)], along with their 95% CIs (calculated using the nlparci.m MATLAB function), were estimated from data collected by Wolfe and colleagues 16 (see Figure 5, top). In this study, healthy subjects performed mild bicycle exercise (PVO 2 max = 40) for 60 minutes.…”

The Pathophysiologic Response to Severe Burn Injury.

“…The fact that the basal rate of glucose production is elevated despite elevated plasma, insulin levels indicates hepatic insulin resistance, since under normal conditions elevated serum insulin would lower the rate of glucose production. 61,65,66 We would like to point out that our values are not fasted values as most of our patients receive continuous feeding via a duodenal tube and we almost never stop feedings. Hyperglycemia is associated with increased mortality in critically ill patients 67,68 and worsens the outcome in severely burned patients.…”