Estradiol stimulation of glucose transport in rat uterus

Glucose transport in rat uterus was investigated in order to determine whether the stimulation of transport by estradiol was the result of an increase in the amount of glucose transport protein in plasma membranes. In cycling rats, transport was highest during proestrus, the day on which serum estradiol concentrations are highest. In ovariectomized rats, the stimulation of transport was estrogen specific and was nearly complete within 2-3 h after injection of 0.1 microgram estradiol per animal. Estradiol stimulation resulted in a 2- to 3-fold increase in Vmax of 2-deoxy-D-glucose transport with no significant change in Michaelis-Menten constant (Km). Inhibition of the stimulation by cycloheximide or actinomycin D could not be demonstrated, although cycloheximide treatment did cause an increase in the basal rate of transport up to that observed with estradiol treatment. Upon polyacrylamide gel electrophoresis followed by Western blotting, a single protein in uterine plasma membranes reacted with a rabbit antiserum made against purified human erythrocyte glucose transport protein. This protein, believed to be the glucose transport protein, had a mol wt of 49,000 and appeared as a broad band as expected for a glycoprotein. It was found by a protein A-linked immunoassay that the amount of transport protein in uterine plasma membranes was 3.2 +/- 0.4% of the amount in human erythrocyte ghosts. Estradiol treatment had no effect on this value. These data suggest that the stimulation of glucose transport by estradiol occurred by an increase in the intrinsic activity of the transport protein rather than by an increase in the amount of transport protein in plasma membranes.