QUANTITATIVE-EVALUATION OF THE EFFECT OF LOW-INTENSITY EXERCISE ON INSULIN-SECRETION IN MAN

We studied insulin secretion rates (ISR) during low-intensity exercise (40% peak aerobic capacity [Vo2]) in 12 normal subjects to assess the contribution of altered insulin secretion to the reduction in peripheral insulin concentrations associated with exercise. ISR were calculated by a previously validated method of two-compartment analysis of peripheral C-peptide concentrations using individual parameters derived following a bolus injection of biosynthetic human C-peptide. In addition, the effect of low-intensity exercise on kinetic parameters of C-peptide was evaluated. The results showed that low-intensity exercise did not significantly affect C-peptide kinetics. Peripheral insulin concentrations and ISR decreased to a similar degree throughout exercise. There was a mean maximum decrease in serum insulin concentrations from 42 ± 5.4 pmol/L basally to 24 ± 2.6 pmol/L, constituting a 51% ± 5.9% decrease (P < .001), and ISR decreased from 85.7 ± 11.9 pmol/min to a nadir of 45.6 ± 10.6 pmol/min (P < .001), a 48% ± 8.4% decline. Plasma glucose and glucagon concentrations did not change significantly either during or after exercise, although there was a matched twofold increase in glucose utilization and disposal rates. We suggest that the reduction in peripheral insulin concentrations during exercise is due to reduced insulin secretion. © 1993.