Renal handling of
sodium and water is abnormal in
chronic kidney diseases. To study the function and regulation of the
aquaporin-2 water channel (AQP2) and the
epithelial sodium channel (ENaC) in
autosomal dominant polycystic kidney disease (
ADPKD), we measured urinary excretion of AQP2 (u-AQP2), the β-subunit of ENaC (u-ENaC(β)), cAMP (u-cAMP), and
prostaglandin E(2) (u-
PGE(2)); free water clearance (C(H2O)); fractional
sodium excretion (FE(Na)); and plasma
vasopressin (p-AVP),
renin (p-
Renin),
angiotensin II (p-ANG II),
aldosterone (p-Aldo), and atrial and
brain natriuretic peptide (
p-ANP, p-BNP) in patients with
ADPKD and healthy controls during 24-h urine collection and after hypertonic saline infusion during high
sodium intake (HS; 300 mmol
sodium/day) and low
sodium intake (LS; 30 mmol
sodium/day). No difference in u-AQP2, u-ENaC(β), u-cAMP, u-PGE(2), C(H2O), and vasoactive
hormones was found between patients and controls at baseline, but during HS the patients had higher FE(Na). The saline caused higher increases in FE(Na) in patients than controls during LS, but the changes in u-ENaC(β), p-Aldo,
p-ANP, p-BNP, p-
Renin, and p-ANG II were similar. Higher increases in u-AQP2 and p-AVP were seen in patients during both diets. In conclusion, u-AQP2 and u-ENaC(β) were comparable in patients with
ADPKD and controls at baseline. In
ADPKD, the larger increase in u-AQP2 and p-AVP in response to saline could reflect an abnormal water absorption in the distal nephron. During LS, the larger increase in FE(Na) in response to saline could reflect a defective renal
sodium retaining capacity in
ADPKD, unrelated to changes in u-ENaC(β).