PALGI, N.*; VATNICK, I.; RONEN, Z.; PINSHOW, B.; Jacob Blaustein Inst. for Desert Research, Ben-Gurion Univ. of the Negev, Midreshet Ben-Gurion, Israel; Widener Univ., Chester, PA, USA; Jacob Blaustein Inst. for Desert Research, Ben-Gurion Univ. of the Negev, Midreshet Ben-Gurion, Israel; Jacob Blaustein Inst. for Desert Research, Ben-Gurion Univ. of the Negev, Midreshet Ben-Gurion, Israel: Effects of salt intake on oxalate balance and calcium absorption in fat sand rats

Fat sand rats Psammomys obesus feed exclusively on plants of the family Chenopodiaceae that contain high concentrations of NaCl and of oxalate salts. Ingestion of large quantities of oxalate is problematic because it chelates Ca2+ cations, reducing the Ca2+ availability. Fat sand rats cope by maintaining a population of oxalate degrading bacteria in their guts, and by eating a diet that is high in NaCl. Sodium chloride increases the solubility of calcium oxalate, freeing Ca2+ for absorption in the body and oxalate ions for bacterial degradation. In feeding trials we found that fat sand rats ingest approximately 300 mg of oxalate per day, more than half of which is not recovered in urine or feces, and therefore is likely degraded by bacteria. The remainder is excreted mainly in the feces, but some in the urine. We found that bacteria in the feces of fat sand rats and maintained in media containing calcium oxalate degraded a significantly higher (P < 0.01) quantity of oxalate when salinity of the medium was 1.2 mol NaCl than at 0.17 mol NaCl. Apparently, a certain quantity of NaCl in the food is necessary for both calcium absorption and oxalate degradation by halophilic bacteria when fat sand rats consume chenopods. To examine how a reduction in NaCl intake affects oxalate and calcium balances, we provided animals with two diets of different salt content: saltbush Atriplex halimus (27% NaCl; 1.7% oxalate), which is the sand rats’ principal diet, and goose-foot Chenopodium album (17.5% NaCl; 1.6% oxalate). We measured intake and excretion of oxalate, calcium and NaCl in animals on the two diets. Significantly more oxalate was degraded when consuming the saltbush, a difference expressed clearly both in oxalate concentration (p < 0.05) and absolute oxalate quantities in the urine (p < 0.01). We propose, therefore, that the high dietary salt intake of sand rats may play a beneficial role in their oxalate and calcium metabolism. This research was funded by student support grants to NP from Sigma Xi and the Mitrani Department for Desert Ecology.