Absolute Rates of Sodium and Potassium Reabsorption by Proximal Tubule of Immature Rats

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Abstract
Using micropuncture procedures, the rate of proximal tubular sodium and potassium transport in mannitol-infused rats has been studied. Tubular diameter and length increase with animal size, but the rates of change are greater in small animals than in larger animals. SNGFR increases with body weight in a linear fashion. Animals from reduced litters have larger SNGFR than do animals from intact litters and males have higher SNGFR than do females. Absolute transport rates for sodium and potassium increase with age and parallel the increases in SNGFR. These results indicate that the predominant factor maintaining proximal glomerular tubular balance as animals grow is an increase in absolute proximal transport rates. With a 50-fold change in SNGFR, change in transport rate accounts for about a 10-fold change, and the rest of the increase in overall proximal absorption is accounted for by an increase in surface area.

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