Brain adaptation to acute hyponatremia in young rats.

Brain swelling after acute hyponatremia in prepubescent rats, in contrast to adults, has recently been associated with an increase in brain sodium and a high mortality that could be prevented by preadministration of testosterone. To reexamine the effect of acute hyponatremia in young brain, we measured brain water and solute content in prepubescent rats after induction of hyponatremia over 4 h with water and arginine vasopressin. An 18% decrease in plasma sodium was associated with a 13% increase in brain water and a decrease in brain sodium and glutamate contents. No animals died. To assess the effect of sex hormones on brain adaptation, prepubescent rats were pretreated with estrogen or testosterone before acute hyponatremia. Brain sodium and potassium contents were significantly reduced in comparison to normonatremia in testosterone-pretreated but not estrogen-pretreated animals. However, there was no difference between estrogen-pretreated and testosterone-pretreated groups in mortality or in brain contents of water, electrolytes, or major organic osmolytes. In conclusion, we found that brain adaptation to acute hyponatremia in prepubescent rats is similar to that observed in adults.