The Relation of Ingested Carbohydrate to the Type and Amount of Blood and Urine Sugar and to the Incidence of Cataract in Rats

Abstract

Blood and urine sugar studies have been made on rats fed on adequate rations containing 62 and 70% lactose, 25 and 35% galactose, 35% fructose, 35% xylose and 70% starch. Determinations of total and nonfermentable sugar were made on both blood and urine specimens from the various ration groups. Total blood sugar values were higher on galactose rations than on lactose but above normal in all animals on cataract producing rations. The nonfermentable fraction of blood sugar was chiefly responsible for the differences in total blood sugar in the various groups, the fermentable fraction remaining more nearly constant and within the range of normal blood glucose. Average total blood sugar values of three strains of rats fed on 35% galactose ration were strikingly similar, in contrast to the differences observed in susceptibility to cataract among the same groups. A fructose-starch ration caused no hyperglycemia and no eye changes. A xylose-starch ration brought about a slight elevation in blood sugar and some early transitory lens changes which did not progress beyond this stage. Insulin-protamine (Lilly) failed to lower blood galactose or reduce the speed of cataract development on a 25% galactose ration. A galactosuria of varying degrees was observed in all rats on lactose and galactose rations, relatively more severe in the latter and absent in starch-fed control groups. It may be concluded that galactose is the sugar responsible for both the high blood and the high urine sugars observed in rats fed on lactose and galactose rations and must be the major etiological factor in this type of cataract.