M. Chacko et al., EFFECT OF MINERALOCORTICOID ACTIVITY ON TRANSTUBULAR POTASSIUM GRADIENT, URINARY [K] [NA] RATIO, AND FRACTIONAL EXCRETION OF POTASSIUM/, American journal of kidney diseases, 32(1), 1998, pp. 47-51
Clinical assessment of potassium derangements may require evaluation o
f mineralocorticoid status. Several indirect indices of mineralocortic
oid activity based on renal electrolyte excretion have been proposed a
nd include the transtubular potassium gradient, urinary [K]/[Na] ratio
, and renal fractional excretion of potassium. We studied the impact o
f high mineralocorticoid activity versus blocked mineralocorticoid act
ivity on these indices in otherwise normal subjects who ingested a def
ined diet. Eight normal subjects received either fludrocortisone or sp
ironalactone for 4 days. After a washout period of greater than or equ
al to 2 weeks, each subject then received the opposite regimen. Subjec
ts ingested an identical high-potassium diet during both experimental
periods. The renal fractional excretion of potassium and transtubular
potassium gradient were calculated using standard formulas, Fludrocort
isone caused an increase in body weight and no significant reduction i
n serum potassium concentration, while spironolactone decreased body w
eight and increased plasma potassium concentration. After 1 or 2 days
of treatment with fludrocortisone, the average values for all urinary
indices of mineralocorticoid activity were significantly higher than a
fter 1 or 2 days of treatment with spironolactone. However, the differ
ences between these indices in the fludrocortisone and spironolactone
test periods diminished by day 3 and were nonexistent by day 4, In con
clusion, the transtubular potassium gradient, [K]/[Na] ratio, and rena
l fractional excretion of potassium reflect acute changes in mineraloc
orticoid activity, However, these indices do not discriminate between
states of high and low mineralocorticoid activity lasting longer than
2 to 3 days. (C) 1998 by the National Kidney Foundation, Inc.