1605 THE EFFECTS OF ALDOSTERONE ON POTASSIUM EXCRETION IN THE DEVELOPING DOG

Abstract

Previous reports from this laboratory have demonstrated the prominent role of aldosterone in the renal tubular transport of Na⁺ in the newborn. The current studies concern the relationship between plasma aldosterone concentration (PAC) and the urinary excretion of K⁺ (U_kV). Mongrel puppies of either sex, 1 or 6-weeks old (n=6 in each group) were anesthetized and infused with increasing amounts of aldosterone. Measurements of PAC were done by radioimmunoassay, whereas serum and urine K⁺ were measured by flame photometry. As expected, a direct relationship obtained between PAC, which varied between 19.1 ± 2.8 and 465.0 ± 37.5 ng/dl in the newborn and 5.0 ± 0.3 and 317.3 ± 36.1 ng/dl in the mature animals, and U_kV. However, the slope of the regression line describing the behavior ot the older animals (y=5.97 ± .02, r²=.83) was significantly steeper (p<.01) than the slope of the regression line depicting this relationship in newborn puppies (y=1.75 + .0001x, r²=.42). On the other hand, there was no difference (p > .3) between the slopes of the regression lines describing the relationship between PAC and U_Na V in the 1 week 2(y=2.00 - .003x, r²=.65) and the 6-week-old animals (y=3.76 - .004x, r²=.44). Thus, aldosterone affects to a larger extent Na⁺ reabsorption than K⁺ excretion during early life. The ensuing retention of both electrolytes should contribute to the positive external balance characteristic of growth.

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