Effects of Exercise and Plane of Nutrition on Nutrient Utilization by the Hind Limb of the Sheep

Abstract

Net uptake, by the hind limb, of O2 and a number of energy substrates was measured in sheep fed semicontinuously at maintenance or 1.5 times maintenance, while standing at rest or walking on a moving-belt treadmill at 0.7 ms-1, on a 10.degree. slope for 60 min. Exercise caused a 6- to 7-fold increase in hind-limb O2 uptake, due mainly to increased blood flow, assisted by an increase in the O2-carrying capacity of arterial blood. Major changes in nutrient supply and utilization included hyperglycemia, hyperlactacidemia, free fatty acid (FFA) mobilization and substantially increased uptakes of glucose and FFA by the hind limb. Acetate uptake was unchanged during exercise in maintenance-fed sheep but was significantly increased in sheep fed at levels above maintenance. Plane of nutrition had little effect on hind-limb uptake of other nutrients in resting or exercising animals. Plasma FFA were clearly the most important respiratory fuels for exercising muscle but a previous finding that acetate utilization was negligible during exercise was not confirmed. Possible reasons for this discrepancy between present and earlier results are discussed.