Distal tubular
sodium retention is a potent driver of
hypertension, and the
thiazide-sensitive sodium-chloride cotransporter (NCC) has a key role in this process. In humans, factors regulating NCC are unclear, but in animal models,
aldosterone is a potent regulator, possibly via effects on plasma
potassium. We studied the effects of the
mineralocorticoid fludrocortisone on the abundance of NCC and its phosphorylated form (pNCC) as well as WNK
lysine deficient
protein kinase 4 (WNK4) and STE20/SPS1-related,
proline alanine-rich
kinase (SPAK) in human urinary exosomes. We isolated exosomes from daily urine samples in 25 patients undergoing
fludrocortisone suppression testing (100 μg every 6 hours for 4 days) to diagnose or exclude primary
aldosteronism. Over the course of the test, NCC levels increased 3.68-fold (P<0.01) and pNCC levels increased 2.73-fold (P<0.01) relative to baseline. The ratio of pNCC/NCC dropped by 48% (P<0.01). The abundance of WNK4 increased 3.23-fold (P<0.01), but SPAK abundance did not change significantly (P=0.14). Plasma
potassium concentration strongly and negatively correlated with pNCC, NCC, and WNK4 abundance (P<0.001 for all). This study shows that, in humans,
mineralocorticoid administration is associated with a rapid increase in abundance of NCC and pNCC, possibly via the WNK pathway. These effects may be driven by changes in plasma
potassium.