Mineralocorticoid activity and the excretion of an oral potassium load in normal man.
In six healthy males on a fixed sodium/potassium (Na/K) intake, we studied the relation between plasma K and urine K and Na excretion after an oral K load. Studies were repeated during fludrocortisone (0.5 mg bid) or spironolactone (50 mg qid), that is, after escape from the Na-retaining and Na-excreting effects of these drugs. A steep positive relation between plasma K (ordinate) and urine K or Na (abscissa) was found, compatible with a strong influence of changes in plasma K on K and Na excretion. Fludrocortisone reset the relation to a lower level of plasma K. Spironolactone, on the other hand, had little effect on these relations, although a tendency towards a higher plasma K could be recognized. Paradoxically, the K load was excreted less efficiently during fludrocortisone, probably due to enhanced cellular K deposition. Prolonged kaliuresis relative to the transient rise in plasma K and natriuresis was found only without medication. Only in this situation aldosterone rose and fell parallel to plasma K. We conclude that: 1) chronic mineralocorticoid increase shifts the set point of both K and Na excretion following a K load to a lower plasma K, compatible with resetting of the positive influence of plasma K on distal solute delivery towards a lower plasma K; 2) total kaliuresis is paradoxically low due to enhanced cellular K uptake; 3) blockade of endogenous aldosterone action has relatively little influence on these relations between plasma K and urine K or Na; 4) the contribution of acute aldosterone stimulation to the excretion of a single oral K load can be recognized as a delayed kaliuresis extending beyond the peak in plasma K.
Hené
R J
RJ
Department of Nephrology and Hypertension, University Hospital Utrecht, The Netherlands.
Koomans
H A
HA
Rabelink
A J
AJ
Boer
P
P
Dorhout Mees
E J
EJ
D000328:Adult; D000450:Aldosterone / Q000378:metabolism*; D005438:Fludrocortisone / Q000494:pharmacology*; D006801:Humans; D007668:Kidney / Q000378:metabolism*; D008297:Male; D009318:Natriuresis; D011188:Potassium / Q000378:metabolism*; D012982:Sodium, Dietary / Q000008:administration & dosage; D013148:Spironolactone / Q000494:pharmacology*
D012982:Sodium, Dietary; D013148:Spironolactone; D000450:Aldosterone; D011188:Potassium; D005438:Fludrocortisone