EFFECT OF GLUCOSE AND GALACTOSE LOADING IN NORMAL SUBJECTS ON RED ANDWHITE BLOOD-CELL URIDINE-DIPHOSPHATE SUGARS

In order to test the assumption that red blood cell (RBC) uridine diph osphate galactose content is regulated in part by dietary galactose an d to help comprehend factors influencing RSC and white blood cell (WBC ) uridine diphosphate hexose concentrations in vivo, oral loading stud ies were performed With 50 g of galactose or 75 g of glucose in normal adults. While elevations of blood glucose did not influence RBC or WB C UDPhexose levels, increased blood galactose concentrations caused tr ansient increases in both RBC and WBC UDPgalactose. In both RBC and WB C, the UDPgalactose-4-epimerase was rate limiting. In comparison to RB C, WBC had larger changes in UDPgalactose levels, synthesized addition al UDPglucose through the action of UDPglucose pyrophosphorylase and b egan to restore the equilibrium ratio between UDPglucose and UDPgalact ose concentrations while the plasma galactose level was still increasi ng. Thus, galactose ingestion alters the steady-state levels of UDPhex oses in circulating cells. The modulation of UDPglucose and UDPgalacto se concentrations, occurring after the presentation of galactose to ce lls, as a result of the combined actions of GALT and UDPgalactose 4-ep imerase, may be important in determining rates of synthesis Of complex glycoconjugates. (C) 1995 Academic Press, Inc.