Increased Na(+)-dependent D-glucose transport in small intestine of retinyl palmitate treated rats

The administration of retinyl palmitate (RP) to rats enhanced Na(+)-dependent D-glucose transport in the small intestine. Effects of RP on Na(+)-dependent D-glucose cotransporter (SGLT1) in rat small intestine were investigated in this study. RP was orally administered (1000 IU/kg/day) to rats for 3 days. The uptake of [3H]D-glucose into the brush-border membrane vesicles (BBMV) of the RP-treated rats, was 1.7-fold larger than that of the control rats. The western blot analysis of SGLT1 protein in BBMV indicated that the amount of SGLT1 was unaffected by the RP treatment. Scatchard analysis of phlorizin binding to both BBMV also showed that the dissociation constant (Kd) and number of phlorizin binding site (Bmax) were unchanged by the RP treatment. The fluidity of the brush-border membrane (BBM) was examined by measuring the fluorescence anisotropy of BBM labeled with 1, 6-diphenyl-1, 3, 5-hexatriene (DPH). The membrane fluidity decreased in the RP-treated rats compared with that of the control rats. In conclusion, the RP treatment increased the glucose transport in BBMV. This enhancement of glucose transport is unlikely due to the change in the amount of SGLT1 protein in BBM. The decrease of the BBM fluidity may contribute to the enhancement of glucose transport in BBM of the RP-treated rats by changing the affinity of SGLT1 for glucose and/or the turnover rate of SGLT1.