Collaboration with Carmi KOrine, Niv Palgi and Berry Pinshow.
Mitrani Department of Desert Ecology Jacob Blaustein Institute for Desert Research, Ben-Gurion University of the Negev, Israel
Buffenstein et al. (1985) found that several species of cricetid rodents from the Namib Desert produced large amounts of a crystalline precipitate in their urine after they were water-deprived for 4 weeks. This precipitate consisted of pure allantoin and it accounted for 29% of the mass of the urine and 30% of the total nitrogen excreted per day. Such a large quantity of allantoin could not be accounted for by purine degradation alone. The production of allantoin instead of urea as the main nitrogenous compound in urine could result in significant water savings. Buffenstein et al. (1985) then posed the question whether the water-stress induced allantoin production is unique to the Namib cricetid rodents. To investigate this question we (Carmi Korine and I – spring 2001 during my sabbatical leave) conducted a preliminary survey of cricetid rodents living in the Negev Desert in southern Israel, to test whether they also produce excess allantoin when subjected to water deprivation Unlike the Namib Desert cricetid rodents, cricetid rodents from the Israeli Negev Desert did not produce large amounts of allantoin precipitate in their urine when deprived of water. There was a precipitate in the urine of Fat sand rats (Psammomys obesus) and Wagner’s gerbil (Gerbillus dasyurus), which was not allantoin. There was no discernable precipitate at all in the urine of Anderson’s gerbil (Gerbillus andersoni allenbyi) and Cairo spiny mouse (Acomys cahirinus. Apparently, Negev Desert cricetids do not share the ability to switch from urea production to allantoin production with the Namib Desert cricetid rodents. We present the results of this study at EB 2002 (see presentations) and published them in the Canadian Journal of Zoology (CJZ_2004.pdf)
In this paper we reported the findings of an oxalate precipitate in the urine of fat sand rats (P. obesus):
“Psammomys obesus produced a precipitate in the urine at all levels of hydration and therefore it was unlikely that this precipitate was related to water conservation. The precipitate in the urine of P. obesus was determined to be sodium oxalate. This should not be very surprising since Atriplex halimus in the Negev contains large amounts of oxalate as well as NaCl (Ellern et al. 1973). Shirley and Schmidt Nielsen (1967) found that P. obesus fed calcium 14C oxalate did not increased their urinary Ca excretion and expired about 25% of the 14C that they were fed in the form of C14O2. Furthermore, when they were fed sodium 14C oxalate they metabolized almost 100% of the oxalate. However, when injected with 14C oxalic acid some animals excreted most of it in their urine, while others oxidized most of it. Shirley and Schmidt Nielsen (1967) suggested that the ability to metabolize oxalate is important for P. obesus. Our results are consistent with this suggestion; it may be that P. obesus, like to pack rats (Neotoma albigula) have the ability to use the calcium in calcium oxalate (Shirley and Schmidt-Nielsen 1967) and then excrete the oxalate in its soluble form (sodium oxalate) in their urine. The results from the ion exchange chromatography indicated that the precipitate contained almost no Ca, rather large amounts of sodium, and that oxalate was found both in the precipitate and liquid portions of the urine. Considering this together with the FTIR analysis of the urine precipitate, we concluded that the precipitate in the urine of P. obesus was sodium oxalate. By excreting sodium oxalate in their urine, P. obesus is able to tolerate high sodium and oxalate dietary intake and therefore consume Atriplex halimus almost exclusively, in spite of its high salt and oxalate content. The question of whether P. obesus can absorb calcium from calcium oxalate requires further investigation.”
From Corine et al 2003
In order to investigate how P. obesus deals with such a high load of oxalate in their diet I collaborate with Niv Palgi in Berry’s lab. Niv wrote a simple research proposal:
The effect of salt intake on oxalate balance and calcium absorption in fat sand rats
Fat sand rats feed exclusively on plants of the family Chenopodiaceae. These plants 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 in the food and also reducing [Ca2+] in the body.
Fat sand rats deal with this problem by:
Maintaining a population of oxalate degrading bacteria in their guts.
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.
Preliminary experiments have shown that fat sand rats ingest approximately 0.15 g of oxalate per day. Half of this quantity is not recovered in urine or feces, and therefore in all probability is degraded by bacteria. Nearly all the rest is excreted in feces. Less than 0.01 g is excreted in urine. Further experiments have shown that bacteria isolated from feces of fat sand rats and kept in media containing calcium oxalate, degraded oxalate much more efficiently when salinity of the media was 7% NaCl compared to media containing only 2% NaCl.
It seems therefore that a certain quantity of NaCl in the food is necessary for both calcium absorption and oxalate degradation when fat sand rats consume their principal diet of chenopods. If NaCl intake decreases acutely, than fat sand rats may not be able to absorb their necessary measure of Ca2+, and bacterial degradation of oxalate will also decrease. The aim of the proposed experiment is to examine how a reduction in NaCl intake affects oxalate balance and calcium absorption in fat sand rats.
Seven adult individuals of fat sand rats (2♂, 5♀) will be used in the experiment. The animals were captured near Kibbutz Sede Boqer and are kept in our laboratory. Animal trapping and keeping was carried out with all the necessary permits. Throughout the experiment, animals will feed on freshly picked plants of Atriplex halimus.
Experiment protocol:
Measurement of oxalate and calcium balance under normal conditions (untreated plats). This will be the control.
Measurement of oxalate and calcium balance when fat sand rats will be fed plants with reduced NaCl content Chenopodium album. This is a plant inb the same family a that contains the same amount of oxalate but half the amount of salt.
To make the measurements, fat sand rats will be transferred to metabolic cages for 24h and will be given 100 g of Atriplex halimus or Chenopodium album plants. All their urine, feces and food remains will be collected. Oxalate, Calcium and NaCl content in will be measured in food plants, urine and feces and thus a balance for all these substances will be determined.”
We conducted the experiment in the summer of 2003 and its results have been submitted to the Comparative Physiology and Biochemistry ( to be posted CPB_2005.pdf).