Postnatal Changes of Water and Electrolytes of Rat Tissues (39545)

Electrolyte and water contents of heart, liver, kidney, spleen, ovaries, and testes were analyzed in rats between 2 and 100 days of age. Tissues were dried to constant weight to measure water content. Electrolyte content was determined using emission spectrophotometry. At all times, the liver contained the least amount of water; the kidney, spleen, and heart had an intermediate water content which were approximately equal to each other; the testes and ovaries contained the highest content of water. Water contents of the liver, heart, spleen, and kidney fall from 2 to 23 days of age and then remain constant at adult levels. The water contents of testes and ovaries remain relatively constant throughout the period studied. Tissue Na content of the heart, liver, kidney, spleen, and testes is high relative to K in the early postnatal period and decreases with age, reaching a minimum at 37-44 days of age. The most unexpected result of this study is the finding that the Na content of the ovary parallels that of the kidney papilla during all the periods examined. In both these tissues, Na content is low at 16 days of age and is higher thereafter. These results demonstrate a dissociation between maturation of water and electrolyte balance. This work was supported by two grants from the National Science Foundation, BMS-72-02344-A02 (to S.S.) and PCM-71-01528 (to A.R.). We also wish to thank Ms. Carolyn Sanborn and Ms. Susan Hathaway for their expert technical assistance.