Adaptation to hyperosmolality in the rat.

Hyperosmolality induced in rats results in a progressive increase in brain glutamine levels with out a change in ammonia. This suggests an adaptation in the compartmental nature of the glutamate-ammonia-glutamine metabolic system to provide more brain osmoles without excess ammonia. The brain: blood glucose ratio rose suggesting brain energy use rate reductions previously reported may be due to altered glucose transport or phosphorylation.