EFFECTS OF HYPERNATREMIA IN THE CENTRAL-NERVOUS-SYSTEM AND ITS THERAPY IN RATS AND RABBITS

1. We studied the effects of acute (1 or 4 h) and chronic (1 week) hyp ernatraemia (plasma [Na+], 170-190 mM) on brain histology, and brain w ater and solute contents in rats and rabbits. 2. In rabbits with acute hypernatraemia, there was significant loss of intracelluar brain wate r, with increases in brain [Na+ + K+], amino acid concentration, and u ndetermined solute (idiogenic osmole). After 1 week of recovery, brain intracellular water content had returned to normal. 3. In hypernatrae mic rats there was myelinolysis of brain white matter, with karyorrhex is and necrosis of neurons. 4. Hypernatraemic rabbits were treated wit h 77 mM NaCl (I.V.) to normalize plasma [Na+] over 4-24 h intervals. T herapy of either acute or chronic hypernatraemia resulted in significa nt brain oedema because brain osmolality failed to decrease at the sam e rate as plasma osmolality. 5. It is concluded that: (a) untreated hy pernatraemia results in brain lesions demonstrating myelinolysis and c ellular necrosis; (b) normalization of hypernatraemia over 4-24 h resu lts in cerebral oedema, due primarily to failure of brain amino acids and idiogenic osmoles to dissipate as plasma [Na+] is decreased to nor mal.