Measurement of flow of carbon atoms from glucose and glycogen glucose to glyceride glycerol and glycerol in rat heart and epididymal adipose tissue. Effects of insulin, adrenaline and alloxan-diabetes

Abstract

1. Flow of carbon atoms from glucose and glycogen glucose to glyceride glycerol, glyceride fatty acids and glycerol was calculated in the perfused rat heart and incubated epididymal adipose tissue from the incorporation of (14)C from [U-(14)C]-glucose (into glyceride glycerol, glyceride fatty acids and glycerol in the medium), and from measurements of the specific activity of l-glycerol 3-phosphate, and the effects of insulin, adrenaline and alloxan-diabetes were studied. Measurements were also made of the uptake of glucose and the outputs of lactate, pyruvate and glycerol. 2. New methods are described for the measurement of radioactivity in small amounts of metabolites (glycerol, glucose 6-phosphate and fructose 6-phosphate and l-glycerol 3-phosphate) in which use has been made of alterations in charge induced by enzymic conversions to effect resolution by ion-exchange chromatography. 3. In hearts the specific activity of l-glycerol 3-phosphate was less than that of glucose in the medium but similar to that of lactate released during perfusion. Because repeated measurements of the specific activity of l-glycerol 3-phosphate was impracticable, the specific activity of lactate has been used as an indirect measurement of glycerol phosphate specific activity. 4. In fat pads, specific activity of lactate was the same as that of glucose in the medium and thus the specific activity of l-glycerol 3-phosphate was taken to be the same as that of medium glucose. 5. In hearts from alloxan-diabetic rats, despite decreased glucose uptake and l-glycerol 3-phosphate concentration, flow of carbon atoms through l-glycerol 3-phosphate to glyceride glycerol was increased about threefold. 6. In fat pads, flow of carbon atoms through l-glycerol 3-phosphate to glyceride glycerol was increased by insulin (twofold), by adrenaline in the presence of insulin (fivefold) and by diabetes in pads incubated with insulin (1.5-fold). These increases could not be correlated either with increases in glucose uptake, which was unchanged by adrenaline and decreased in diabetes, or with the concentration of l-glycerol 3-phosphate, which was decreased by adrenaline and unchanged in diabetes. 7. These results are discussed in relation to the control of glyceride synthesis in heart and adipose tissue and to the regulation of glyceride fatty acid oxidation in the perfused rat heart.