α-Glycerophosphate metabolism in muscle under aerobic and hypoxic conditions

Abstract

A significant amount of α-glycerophosphate (α-GP) was present in voluntary skeletal muscle of rats when the hind limb was frozen in situ. Ischemia of this muscle in situ caused a 7-fold increase in α-GP concentration and a 12-fold increase in lactate concentration. In vitro experiments with diaphragm muscle from rats and adductor fiber groups from rats and monkeys also demonstrated that hypoxic conditions caused a 2.5- to 4-fold rise in α-GP levels. The α-GP concentration in hypoxic red muscle was higher than that in hypoxic white muscle from rats. Lactate diffused into the medium from all types of muscle preparations. However, under aerobic conditions no measurable amount of α-GP appeared in the medium surrounding the fibers and only a small amount diffused out of the diaphragm muscle. Even when incubation was carried out under hypoxic conditions little α-GP was present in fiber medium. Although the diaphragm released ten times as much α-GP as the fiber groups, this amount was small in relation to lactate production. These data indicate that under anaerobic and hypoxic conditions dihydroxyacetone phosphate can compete with pyruvate for the cytoplasmic NADH in diaphragm and voluntary skeletal muscle.