Brain Potassium Exchange in Normal Adult and Immature Rats

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Abstract
Sixty-eight normal adult male rats were injd. intraperit. with radioactive K. The animals were decapitated at intervals of 4, 16, 39, 54, and 72 hrs. , and plasma and brain activity and total K measured. The general exchange equation, [image] was solved by graphical methods for the transport coefficients k1 and k2 and from these values the influx and outflux were calculated. Similar studies were done on 4, 15, and 35-day and greater than 18-mo. animals. The influx of K into the brain of normal adult rats was found to be 2.89 m.eq./kg./hr.; the outflux rate 3.64 m.eq./kg./hr. and the influx/outflux ratio 0.80. Since a steady state obtains, the outflux must be equivalent to influx. Therefore 20 m.eq.K/kg. of wet brain is not exchangeable with K42, The influx in 4-day- and 15-day-old animals is 3.9 m.eq./kg-/ hr. and in 35-day animals the influx is 3.1 m.eq./kg./hr. All brain K was found to be exchangeable in 4, 15, and 35-day rats. Brain K exchange in older rats is similar to that of normal young adults.