Labelled Insulin Catabolism and Pancreatic Responsiveness During Long-Term Exercise in Man

Abstract

Most studies coneerning the influence of exercise on insulin secretion, only dealt with the level of plasma IRI. Dur aim was to measure both insulin catabolism and pancreatic responsiveness.Muscular exercise (bicycle ergometer, Power 80 W, workload 40% of max V02), maintained in steady state of ven-. tilation during 40 min, was performed by several groups of normal subjects. The following results were obtained.(1) In normoglycemia or in hyperglycemia caused by glucose infusion, exercise induced no decrease in plasma IRI level Hl The metabolie clearance rate of a constant infusion of I-insulin (0.2 atom I/mol) showed a reduction averaging 17% whereas no change in extracellular spaee could be detected. This decrease in insulin catabolism was associated with a similar decrease in the clearanee rates of labelIed hippuran and BSP. (3) Insulin response to glucagon injection was markedly reduced. (4) Plasma norepinephrine levels were increased.In conclusion, the absenee of change in plasma IRI level often described in non strenuous exercise results from the balance of two antagonistic phenomena: a decreased secretion rate probably related to the release of endogenous catecholamines and a decreased catabolic rate, apparently due to changes in liver and kidney haemodynamics. Horm. Metab. Res. 3: 366·373 (1971) K e y -W 0 r d s: Exercise -Plas1TU1 Glucose -PlaS1TU1 Insulin -LabelIed Insulin Catabolillm -Response to Glu· cagon -BSP -Hippuran -Catecholamines IntroductionMost studies concerning the influence of muscular exercise on insulin metabolism only dealt with estimations of plasma insulin concentrations. The results depended on the importance of the work load and on the duration of its performance. In normal subjects, mild exercise or moderate exercise of short duration elicits no systematic or significant change in the level of plasma insulin (Rasio, Malaisse, Franckson and Conard 1966, Cochran, Marbach, Poucher, Steinberg and Gwinup 1966, Schalch 1967

Exercise increases insulin clearance in healthy man and insulin‐dependent diabetes mellitus patients

“…In the current study, there was evidence of augmented insulin clearance after exercise both in the fasting state and during hyperinsulinaemia in healthy subjects. The fasting insulin, but not C-peptide, concentrations were reduced 12 h after the exercise in healthy men, consistent with earlier reports (Wright & Malaisse, 1968;Franckson et al, 1971;Hilsted et al, 1980;Wirth et al, 1981), suggesting that decreased insulin concentration was a result of enhanced insulin clearance rather than reduced insulin secretion (Franckson et al, 1971;Hilsted et al, 1980;Wirth et al, 1981). When examined 44 h after the treadmill exercise, fasting C-peptide levels were decreased possibly reflecting an exercise-induced decrease in insulin secretion.…”

“…Regular physical activity reduces insulin secretion both in the fasting state (Wright & Malaisse, 1968;Franckson et al, 1971;Hilsted et al, 1980;Wirth et al, 1981) and in response to glucose challenge (King et al, 1987(King et al, , 1988Mikines et al, 1989). This is related to improvement in insulin sensitivity, which is observed both in healthy men (Mikines et al, 1988b) and in IDDM (Wallberg-Henriksson et al, 1982;Yki-Järvinen et al, 1984;Koivisto et al, 1986;Mandroukas et al, 1986) or non-insulin-dependent diabetes mellitus (NIDDM) patients (Devlin, 1992).…”

Regulation of Extramuscular Fuel Sources During Exercise

“…For this reason changes in insulin secretion will lead to smaller changes in arterial insulin levels (304). The reduction in insulin levels with exercise is due to a decrease in~-cell secretion, as evidenced by a fall in C-peptide levels (51,121,178,267,326), decreased net insulin release from extrahepatic splanchnic tissue (pancreas inclusive) (304), and an increase in plasma insulin-specific activity during isotopic insulin infusion (90). The magnitude of the fall in insulin levels is directly related to work duration.…”

Kinetic Analysis of Plasma Insulin Disappearance in Nonketotic Diabetic Patients and in Normal Subjects

“…In most study subjects, the metabolic status, evaluated in this way, was reasonably well controlled. 34 (14). By all these procedures, the labeled protein was split from the unreacted iodine, as shown by paper electrophoresis.…”