The rate and pattern of glucose metabolism by slices of epididymal adipose tissue from ad libitum-fed rats, hamsters and guinea pigs were studied in an in vitro incubation, at three stages of development during the first year of the animals' lives. The results were expressed on the basis of fat cell number and in relation to the fat cell size. The responsiveness of the adipose cells to the glucose-transport stimulating effect of bovine insulin was determined in relation to the age of the animals and to the adipocyte volume. The data indicate that the amounts of basal glucose metabolized to [CO2 + triglyceride] per fat cell remained relatively constant in each of the three species, even though the fat cell volumes varied markedly. In concomitance with fat cell enlargement, the pattern of glucose metabolism exhibited a progressive change, with reduction in the proportions of glucose converted to CO2 and glyceride-fatty acid and a significant increase in that of glucose converted to glyceride-glycerol.

The effect of bovine insulin in stimulating glucose transport and metabolism varied from species to species being greatest in the rat and smallest in the guinea pig fat cells. In each species, the magnitude of the response to bovine insulin was found to be decreased as the fat cells enlarged with age and ad libitum feeding of the animals. The guinea pig differed from the other two species in the limited capacity of the fat cells to enlarge during the period of observations. In spite of the small fat cell size, the response of guinea pig fat cells to bovine insulin was minimal. During growth and development of the animals, fat cell number, baseline rate of glucose metabolism and responsiveness to insulin contribute to the over-all glucose metabolism by the epididymal fat pads; in the guinea pig, the contribution of fat cell number appeared to be quantitatively more important than the stimulatory effect of insulin.

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