myo-inositol: a newly identified nonnitrogenous osmoregulatory molecule in mammalian brain.

Sugar alcohols have been found to play an important osmoregulatory role both in unicellular organisms and, more recently, in multicellular organisms, including mammals. This study shows that myo-inositol accumulates in the brains of chronically hypernatremic mice, as had been earlier found in rats, and demonstrates for the first time a profound decrease of myo-inositol in the brains of chronically hyponatremic mice. Together with decreases in better known cerebral osmoles (amino acids and related nitrogenous compounds), the decrease in myo-inositol apparently allows the brain to balance its intracellular osmolality with that of the plasma, permitting a normal brain water content (no edema) despite profound hyponatremia.