Insulin does not mediate the attenuation of fatigue associated with glucose infusion in rat plantaris muscle

Abstract

Glucose infusion attenuates fatigue in rat plantaris muscle stimulated in situ, and this is associated with a better maintenance of electrical properties of the fiber membrane (Karelis AD, Péronnet F, and Gardiner PF. Exp Physiol 87: 585-592, 2002). The purpose of the present study was to test the hypothesis that elevated plasma insulin concentration due to glucose infusion ( approximately 900 pmol/l), rather than high plasma glucose concentration ( approximately 10-11 mmol/l), could be responsible for this phenomenon, because insulin has been shown to stimulate the Na+-K+ pump. The plantaris muscle was indirectly stimulated (50 Hz, for 200 ms, 5 V, every 2.7 s) via the sciatic nerve to perform concentric contractions for 60 min, while insulin (8 mU x kg-1x min-1: plasma insulin approximately 900 pmol/l) and glucose were infused to maintain plasma glucose concentration between 4 and 6 [6.2 +/- 0.4 mg x kg-1x min-1: hyperinsulinemic-euglycemic (HE)] or 10 and 12 mmol/l [21.7 +/- 1.1 mg. kg-1. min-1: hyperinsulinemic-hyperglycemic clamps (HH)] (6 rats/group). The reduction in submaximal dynamic force was significantly (P < 0.05) less with HH (-53%) than with HE and saline only (-66 and -70%, respectively). M-wave characteristics were also better maintained in the HH than in HE and control groups. These results demonstrate that the increase in insulin concentration is not responsible for the increase in muscle performance observed after the elevation of circulating glucose.