1. Archive
2. Vol.51, No.6

Development of Renal Potassium Excretion Capacity in the Neonatal Rat

Abstract: We investigated the capacity of newborn rats to excrete an acute potassium load to understand the development of a renal potassium excretion system. Three groups of the rats (7-14 d) were used to collect urine periodically over 6 h after oral infusion of potassium: control (no potassium loading) and low- and high-potassium-loaded rats. In the low-potassium-loaded group, infused with about 0.6 Eq of potassium chloride/g body wt., the rate of renal potassium excretion increased from 0.08 ± 0.02 (7 d) to 0.13 ± 0.02 (10 d) and 0.21 ± 0.03 (14 d) Eq/h/g body wt. The high-potassium-loaded rats (1.5-2.8 Eq/g body wt. potassium load) excreted potassium at a higher rate of 0.18 ± 0.05 (7 d), 0.30 ± 0.02 (10 d), and 0.45 ± 0.10 (14 d) Eq/h/g body wt. They excreted 77% (7 d), 76% (10 d), and 95% (14 d) of the potassium load. These values were much larger than the rate of 0.026 Eq/h/g body wt. of the control rats and of 0.08 Eq/h/g body wt., a mean potassium excretion rate during development from 7 to 14 d calculated from the data in the previous study (Kanno T et al.: J. Pediatr. Gastr. Nutr. 24: 242-252, 1997). In the same period, serum potassium concentration in the newborn rats decreased significantly (p < 0.01) from 7.2 ± 0.1 (7 d) to 6.7 ± 0.1 mEq/l (14 d). All these results suggest that a renal potassium excretion system in the rat develops at least in the second week of life, and its capacity is high enough to excrete the daily potassium intake.

[Full Text (PDF)]