Effects of insulin on the uptake of d-galactose by isolated rat epididymal fat cells

In muscle, insulin stimulates uptake of d-galactose as well as d-glucose and certain other sugar isomers (Kono, T. and Colowick, S.P. (1961) Arch. Biochem. Biophys. 93, 514–519). In fat cells, the hormone also stimulates uptake of d-glucose and certain other monosaccharides. Nonetheless, the hormone does not increase the uptake, as determined by the utilization, of d-galactose by fat cells (Ball, E.G. and Cooper, O. (1960) J. Biol. Chem. 235, 584–588; Kuo, J.F. and Dill, I.K. (1969) Biochim. Biophys. Acta 177, 17–26).As pointed out by Ball and Cooper, this does not necessarily indicate that insulin has no effect on the membrane transport of d-galactose in fat cells. The possible effect of the hormone on transport may not be seen in the utilization data if the intracellular metabolism is considerably slower than the rate of transport and insensitive to insulin.