Calciuria in total parenteral nutrition: effects of amino acids and glucose in rats

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Abstract
Total parenteral nutrition (TPN) is known to cause hypercalciuria and negative calcium balance in some patients. We have now shown that the administration of TPN to rats causes marked increases in urinary calcium losses. Moreover, urinary calcium excretion in the TPN rat responds to changes in the infusate concentration of calcium and amino acids similarly to what has been observed in TPN patients. For any given increase in the amount of calcium infused 130% more calcium was excreted in the urine by rats receiving TPN compared to rats receiving saline alone. At a fixed level of calcium infused, urinary calcium increased linearly when the amino acid content of the infusate was increased from 0 to 2.75 to 4.25%. However, a reduction in the glucose load, via isocaloric substitution with lipid by 60%, had no effect on urinary calcium excretion. The TPN rat appears to be a promising animal model in which to investigate the hypercalciuretic effect of intravenous nutrition, particularly as calcium homeostasis may be affected by various nutritional components of the TPN solution.