HDCN Abstract:  Am Soc Nephrol Ann Mtg -- Toronto  

Ghanekar HP, Lerma EV, Batlle D

Dietary sodium determines the effects of potassium depletion on urinary acidification

Am Soc Nephrol Ann Mtg -- Toronto
J Am Soc Nephrol (Sep) 11:105A 2000

K depletion has been shown to result in a variable change in net acid excretion(NAE)for reasons that are not clear. Differences in Na balance may account for this variability since dietary Na restriction amplifies the metabolic alkalosis generated by K depletion. We reasoned that a high Na diet, during K depletion, should lead to a decrease in NAE, because of the associated stimulus for renal Na retention provided by K depletion which should suppress aldosterone and stimulate ANP which would decrease NAE.

Two groups of healthy male volunteers were studied in our Clinical Research Center while placed on a synthetic diet with a K content of 1.5mEq/kg BW. After a precontrol period of 4 days, the subjects were kept on the same diet for 5 days and then switched to zero K diet while maintaining the dietary Na constant (1.8mEq/Kg BW) (Gr 1) or while increasing dietary Na to 3.3 mEq/Kg BW by substituting potassium phosphate with neutral sodium phosphate. (Gr 2).

In Gr 1, dietary restriction of K over a nine day period decreased urinary Na (from 174 ± 22 to 67 ± 9 mEq/24 hrs) resulting in a cumulative Na retention of 568 ± 80 meq.Titratable acidity decreased from 64 ± 9 to 33 ± 8 mEq/24hrs (p<0.01) and NH4 increased from 30 ± 3.6 to 65 ± 9.8 mEq/24 hrs.(p<0.005). This increase in NH4 excretion was seen despite of a fall in the urinary aldosterone (from 10±4 to 2.8±2 mg/24 hrs).

In Gr 2, where K depletion resulted in a greater cumulative Na Balance of 899± 90mEq. (P<.01), urinary pH increased from 5.3 ± 0.006 to 6.1 ± 0.004 (p< 0.0005), tritratable acidity decreased from 90 ± 12 to 55 ±4 mEq/24 hrs. (p<. 005) and NH4 decreased (from 48 ± 6 to 38 ± 3mEq/24 hrs) (p<0.05), so that the NAE decreased (from 143 ± 16 to 92 ± 8 mEq/24 hrs) (p<0.005).

The results indicate that K depletion causes Na retention which, in the presence of excess dietary Na, causes volume expansion and a decrease in NAE. Thus metabolic acidosis rather than metabolic alkalosis is the acid base disorder expected in situations where K depletion coexist with marked volume expansion and aldosterone suppression.

Copyright 2000, American Society of Nephrology