Oxalic acid metabolism in the rat.

Feeding experiments indicated that approximately 15% of dietary oxalate is adsorbed in the rat intestine and that dietary oxalate accounts for about one third of the oxalic acid normally excreted in rat urine. Oxalate excretion increased by about 40% when a low calcium diet was fed, decreased by 65% when a low protein diet was fed and increased by 100% when a high protein diet was fed. Fasting for 24 hours resulted in a fall in calcium excretion but phosphate and creatinine excretion increased. Oxalate excretion also tended to increase. Between 60% and 70% of activity was recovered in the urine, faeces and body tissues after 14C-oxalic acid had been administered intraperitoneally. Recoveries of 14C-labeled compounds as urinary 14C-oxalic acid decreased in the following order: glyoxylic acid greater than ascorbic acid greater than citric acid greater than glycollic acid greater than tryptophan greater than hydroxyproline greater than glycine. It is suggested that conversion of citrate to oxalate in the rat may occur via the "glyoxylate cycle." It is concluded that a higher proportion of dietary oxalate is absorbed in the rat intestine compared with man, and that dietary oxalate accounts for a higher proportion of urinary oxalate in the rat than in man. Intestinal secretion and bacterial degradation of oxalate also appear to be proportionately greater in the rat than in man.