THE ROLE OF ALDOSTERONE IN RENAL ELECTROLYTE TRANSPORT DURING DEVELOPMENT

Abstract

Indirect evidence has led us to postulate a cause and effect relationship between the high levels of plasma aldosterone concentration (PAC) and the positive electrolyte balance prevailing during infancy. The purpose of this study was to assess directly the relationship between PAC and renal transport of Na+ and K+. PAC measurements and renal clearance of Na+ and K+ were performed in 1 and 6-week-old puppies that received a 5% saline solution, 15 ml/kg b.w. for 3 consecutive days i.p. (E), and in age matched sham operated controls (C). The same variables were then measured during i.v. infusion of increasing amounts of aldosterone (5,10, and 20 μg/kg b.w. for 2 hrs each). In sodium loaded animals, the changes in urinary Na+/K+ ratio were inversely proportional to those in PAC and significantly larger (p < .01) in newborn (from 1.22 ± .32 to 2.38±.60) than in mature dogs (.71 ± .52 to .98 ± .17). The relationship between PAC and Na+/K+ during aldosterone infusion differed between C and E being described respectively by the equations y=1.35-.002x (r=.89) and y=2.25-.005x (r=.94) in the 1-week-old (p<.05), and y=.71-.0002x (r=.99) and y=1.36+.006x (r=.67) in the 6-week-old (p < .05). A direct relationship was observed in each group between PAC and K+ excretion (ΔUKV). However, the slope of the regression line describing the relationship between PAC and ΔUKV was significantly steeper (p <.01) in adults (y=1.32+.02x, r=.73) than in newborn puppies (y=1.04+.003x, r=.64). Thus, the effect of aldosterone on renal Na+ reabsorption is maximal, while the effect on K+ secretion is minimal, during the neonatal period. The resulting retention of both Na+ and K+ is concordant with the needs of the growing organism.