Increased muscle glucose uptake during contractions: no need for insulin.

We reinvestigated the prevailing concept that muscle contractions only elicit increased muscle glucose uptake in the presence of a so-called "permissive" concentration of insulin (Berger et al., Biochem. J. 146: 231-238, 1975; Vranic and Berger, Diabetes 28: 147-163, 1979). Hindquarters from rats in severe ketoacidosis were perfused with a perfusate containing insulin antiserum. After 60 min perfusion, electrical stimulation increased glucose uptake of the contracting muscles fivefold. Also, subsequent contractions increased glucose uptake in hindquarters from nondiabetic rats perfused for 1.5 h in the presence of antiserum. 3-O-methylglucose uptake was increased markedly by contractions in fast-twitch red and white fibers that were severely glycogen depleted but not in slow-twitch red fibers that were not glycogen depleted. In hindquarters from ketoacidotic rats perfused exactly as by Berger et al., 3-O-methylglucose uptake increased during contractions and glucose uptake was negative at rest and zero during contractions. An increase in muscle transport and uptake of glucose during contractions does not require the presence of insulin. Furthermore, glucose transport in contracting muscle may only increase if glycogen is depleted.