Effects of sugars and vitamin B-6 deficiency on oxalate synthesis in rats

Rats fed diets containing galactose as the source of carbohydrate excreted greater amounts of endogenously formed oxalic acid in their urine, compared to rats fed glucose, fructose or sucrose. Rats fed lactose showed similar but less marked effects. The greatest amounts of urinary and fecal oxalate excretions were observed among rats fed galactose and no vitamin B-6. This group had the lowest body weights after 3 weeks of feeding. Control rats fed galactose or lactose diets weighed less than those fed sucrose, glucose or fructose diets. All rats fed galactose developed cataracts. More [14C]oxalic acid was recovered in the urine and kidneys of control rats injected with D-[U-14C]galactose compared to those injected with D-[U-14C]glucose or D-[U-14C]fructose. Similar results were observed in kidneys of vitamin B-6-deficient rats. The possible mechanisms by which galactose and other sugars may be converted to oxalate are discussed.