This is a study of the effect of insulin on the transport of K+ and Na+ from the blood into the brains of normal mice. Despite profound reductions in plasma and brain glucose levels, reduction of plasma K+ concentration and progressive deterioration of neurologic function 30–120 minutes after insulin injection, in 20–22-day-old animals there was no increase in brain K+ and Na+ concentrations. In fact, at 120 minutes, when the brain water content increased 0.7 per cent, brain K+ concentration was significantly reduced, not elevated.

The effect of insulin on brain electrolyte and water content in adult mice was also studied. Although brain water increased 0.5 per cent at 120 minutes, there was no changes in brain Na+ or K+ concentrations at any time after insulin injection.

The data from mice do not support a role of insulin in electrolyte transport in brain.

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