Contribution of blood flow to leg glucose uptake during a mixed meal

Insulin has important effects to increase skeletal muscle (leg) blood flow under euglycemic hyperinsulinemic clamp conditions and after oral glucose tolerance testing. The present studies examined the effects of mixed meal consumption on the components of leg glucose uptake (LGU) in lean, healthy adults. Seventeen men and women underwent measures of leg plasma flow and arteriovenous (AV) glucose difference before and for 6 h after a mixed meal providing one-third of daily energy expenditure. Another eight men and women underwent the same studies before and during the consumption of the same-size meal administered in small frequent feedings over 6 h. After the bolus meal, peak leg AV glucose gradient increased approximately fivefold (P < 0.001), whereas the peak increase in leg plasma flow was 20% (NS). No significant contribution of increased leg blood flow to the increase in postprandial LGU was apparent. Over the last 100 min of the frequent-feedings meal, the leg AV difference increased approximately fourfold (P < 0.001 vs. basal), whereas leg blood flow increased only by 16% (NS vs. basal). We conclude that after a mixed meal, leg (primarily skeletal muscle) blood flow does not increase enough for blood flow to be a major contributor to glucose uptake. These findings raise questions regarding the relative importance of insulin's hemodynamic effects in modulating glucose tolerance under more usual conditions.