Urinary oxalic acid excretion differs after oral loading of rats with various oxalate salts.
BACKGROUND
To compare urinary oxalate excretion after the oral administration of oxalic acid, disodium oxalate, or calcium oxalate in rats.


METHODS
Male Wistar rats were divided into four groups of six rats each and were intravenously hydrated with normal saline, and then were administered normal saline (control group), 10 mg of oxalic acid, equimolar disodium oxalate, or equimolar calcium oxalate via a gastrostomy. Urine specimens were collected just before administration and at hourly intervals up to 5 h afterwards. The urinary oxalate, calcium, magnesium and phosphorus levels were measured.


RESULTS
Urinary oxalate excretion peaked at 1-2 h after administration of oxalic acid or equimolar disodium oxalate, while administration of calcium oxalate only caused a small increase of urinary oxalate excretion. Cumulative urinary oxalate excretion during 5 h was 1.69 +/- 0.10 mg (mean +/- SD; 17%), 1.43 +/- 0.13 mg (13%), and 0.22 +/- 0.03 mg (2%) after the administration of oxalic acid, disodium oxalate, and calcium oxalate, respectively. Urinary calcium excretion showed a decrease in the oxalic acid and disodium oxalate groups, while urinary magnesium or phosphorus excretion did not change significantly.


CONCLUSIONS
The upper gastrointestinal tract seems to be the major site of oxalic acid absorption and only free oxalate is absorbed irrespective of whether it is the sodium salt or not. After binding to calcium in the gut, oxalic acid absorption seems to be inhibited in the presence of calcium and this means that calcium oxalate is poorly absorbed (at least in the upper gastrointestinal tract).
Hossain
Rayhan Zubair
RZ
Department of Urology, Faculty of Medicine, University of the Ryukyus, Nishihara, Okinawa, Japan. k008744@med.u-ryukyu.ac.jp
Ogawa
Yoshihide
Y
Morozumi
Makoto
M
Sugaya
Kimio
K
Hatano
Tadashi
T
D000284:Administration, Oral; D000818:Animals; D002118:Calcium / Q000652:urine; D002129:Calcium Oxalate / Q000008:administration & dosage / Q000493:pharmacokinetics*; D004064:Digestive System / Q000378:metabolism; D007408:Intestinal Absorption / Q000502:physiology; D008274:Magnesium / Q000652:urine; D008297:Male; D010070:Oxalates / Q000008:administration & dosage / Q000652:urine*; D019815:Oxalic Acid / Q000008:administration & dosage* / Q000493:pharmacokinetics*; D010758:Phosphorus / Q000652:urine; D051381:Rats; D017208:Rats, Wistar; D019163:Reducing Agents / Q000008:administration & dosage*; D012016:Reference Values; D013997:Time Factors
D010070:Oxalates; D019163:Reducing Agents; D002129:Calcium Oxalate; D010758:Phosphorus; D019815:Oxalic Acid; D008274:Magnesium; D002118:Calcium