Rapid correction of severe hyponatremia in the rat: histopathological changes in the brain

The purpose of the present studies was to examine the effects of rapid correction of severe hyponatremia (serum sodium less than 120 meq/liter) either to mildly hyponatremic levels (serum sodium = 130 meq/liter) or to normonatremic levels (serum sodium = 150 meq/liter) on the brain histology of rats. In group I, 13% of the rats revealed brain lesions following correction to mildly hyponatremic levels by the administration of 855 mM NaCl. All the rats (100%) in group II had brain lesions following correction to normonatremic levels by 24 h of water restriction. Similarly, all the rats in group III showed brain lesions following correction to normonatremic levels by the administration of 855 mM NaCl. Severe hyponatremia by itself did not cause any brain lesions in another group. We conclude that rapid correction of severe hyponatremia to mildly hyponatremic levels by the administration of 855 mM NaCl does not cause significant brain lesions. On the other hand, rapid correction to normonatremic levels either by water restriction or by the administration of 855 mM NaCl results in significant brain lesions.