The measurement of exchangeable sodium and total body sodium in rats in vivo compared with chemical analysis postmortem.

Measurements of body sodium content in rats were made in vivo by either neutron activation analysis or the use of the radioisotope, 22Na. The results were compared with estimates of TBNa of the carcases. Neutron activation analysis provided an accurate measure of total body sodium content. NaE, measured with 22Na, was consistently and quantitatively lower than total body sodium content. Each of these methods may be useful in the study of body sodium content in small animals during growth and during the evolution of experimental hypertension.