Glucose uptake and phosphorylation in fat cells of fasted and hypophysectomized rats

Fat cells of hypophysectomized and fasted rats metabolize 10 times less glucose than adipocytes of normal rats in the presence of insulin. Glucose transport (3-O-methylglucose influx), transport plus phosphorylation (2-deoxyglucose uptake), hexokinase, pyruvate dehydrogenase and glucose-6-phosphate dehydrogenase activities were determined in an attempt to localize the metabolic defects. Insulin stimulates 3-O-methylglucose influx 5-fold in normal cells and 3-fold in cells of fasted rats. The basal influx in cells of fasted rats is increased and even more so in cells of hypophysectomized rats where the rate of basal influx is the same as that in cells of normal rats under maximal insulin stimulation. It cannot be further stimulated by insulin. In contrast to 3-O-methylglucose influx, basal uptake and phosphorylation of 2-deoxyglucose in cells of fasted and hypophysectomized rats is drastically decreased and stimulation by insulin is abolished. Total hexokinase and pyruvate dehydrogenase activities are drastically reduced in the homogenate of fat cells of hypophysectomized and fasted rats. Phosphorylation by hexokinase appears to become one of the rate-limiting steps of glucose metabolism in cells of hypophysectomized rats.