Effects of hydroxyproline and vitamin B-6 on oxalate synthesis in rats.

Relationships among dietary hydroxyproline (HP), vitamin B-6 and endogenous oxalate formation have been studied. In the absence of HP, urinary oxalate excretion was greatest among rats fed vitamin B-6-deficient diets. Supplementation of rat diets with 5.2% HP markedly increased the oxalate excretion of rats fed 0, 0.2 or 10 mg of vitamin B-6 per 100 g of diet, the increases being 2-, 19- and 15-fold respectively. The metabolism of several 14C-labeled oxalate precursors was altered in vitamin B-6-deficient rats. The feeding of HP and different levels of vitamin B-6 also altered their metabolism. The feeding of HP to vitamin B-6-deficient rats resulted in a decrease in the amount of 14C-oxalate formed from injected 14C-labeled glycine, glycolate or glyoxylate. In contrast, HP feeding to rats given 0.2 mg of vitamin B-6 per 100 g, resulted in a marked increase in oxalate formation from injected 14C-glycolate, as well as a decrease in respiratory 14CO2 from injected 14C-labeled glycolate and glyoxylate. HP feedings did not significantly alter the metabolism of these two injected compounds to oxalate or CO2 among rats fed the higher level of vitamin B-6, although some elevation of oxalate formation from glycolate was noted. HP feeding reduced the growth rates of all the rats, but growth depression was greatest in the vitamin B-6-deficient group.