Gastrointestinal tract strontium

Taylor DM, Bligh PH, Duggan MH. 1962. The absorption of calcium, strontium, barium and radium from the gastrointestinal tract of the rat. Biochem J 83 25- 29. 

The exact site of absorption of strontium in the gastrointestinal tract is not known however, studies in hamsters suggest the possibility of absorption in both the stomach and small intestine. In hamsters that received a gavage tracer dose of 85SrCl2, 37% was absorbed, whereas 20% was absorbed when the dose was administered to hamsters that had their pyloric sphincter ligated (Cuddihy and Ozog 1973). Studies in preparations of in vitro and in situ isolated intestine of the rat provide direct evidence for strontium absorption in the small intestine (see Section 3.5.1). 

Information on the distribution of strontium absorbed after deposition in the respiratory tract can be derived from studies in which strontium compounds were instilled directly into the trachea. Although intratracheal instillation does not mimic inhalation exposure, the distribution of the absorbed strontium is likely to be similar to that which would be absorbed after inhalation. In rats that received an intratracheal dose of 89Sr-enriched fly ash (sieved to have a particle diameter of distribution of 90% less than 20 pm), radioactivity was eliminated from the lung and appeared in plasma and other tissues within days of the exposure tissue plasma concentration ratios were >1 (1.5-2) in the liver, kidney, stomach, and small intestine, and <1 (0.7-0.9) in the spleen, heart, and brain (Srivastava et al. 1984b). The relatively high concentrations of strontium in the gastrointestinal tract may reflect the mechanical clearance of strontium from the airways to the esophagus. 

Strontium that has been absorbed from the gastrointestinal tract is excreted primarily in urine and feces. In two dial painters, rates of urinary and fecal excretion of radium approximately 10 years after the exposure were approximately 0.03 and 0.01% of the body burden, respectively (Wenger and Soucas 1975). The urine fecal excretion ratio of 3 that was observed in the radium dial workers is consistent with ratios of 2-4 observed several days to weeks after subjects received an intravenous injection of SrCl2 (Bishop et al. 1960 Blake et al. 1989a, 1989b Newton et al. 1990 Samachson 1966 Snyder et al. 1964 Uchiyama et al. 1973). Thus, urine appears to be the major route of excretion of absorbed strontium. The observation of fecal excretion of radioactive strontium weeks to decades after an oral exposure or over shorter time periods after an intravenous exposure suggests the existence of a mechanism for transfer of absorbed strontium into gastrointestinal tract, either from the bile or directly from the plasma. Evidence for direct secretion of strontium from the plasma into the intestine is provided by studies in animals (see Section 3.5.1). The available information does not address the extent to which biliary excretion may also contribute to fecal excretion of strontium. 

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