Angiotensin II-mediated hypertension impairs nitric oxide-induced NKCC2 inhibition in thick ascending limbs

• Published in: American journal of physiology. Renal physiology Vol. 310; no. 8; pp. F748 - F754
• Main Authors: Ramseyer, Vanesa D, Ortiz, Pablo A, Carretero, Oscar A, Garvin, Jeffrey L
• Format: Journal Article
• Language: English
• Published: United States American Physiological Society 15.04.2016
• Subjects: Angiotensin II; Animals; Cyclic CMP - analogs & derivatives; Cyclic CMP - pharmacology; Cyclic GMP - metabolism; Cyclic Nucleotide Phosphodiesterases, Type 5 - metabolism; Endothelin-1 - pharmacology; Hypertension; Hypertension - chemically induced; Hypertension - metabolism; Loop of Henle - drug effects; Loop of Henle - metabolism; Male; Nitric oxide; Nitric Oxide - metabolism; Nitric Oxide Donors - pharmacology; Phosphodiesterase 5 Inhibitors - pharmacology; Proteins; Rats; Rats, Sprague-Dawley; Rodents; Solute Carrier Family 12, Member 1 - metabolism; Vardenafil Dihydrochloride - pharmacology; kidney; cGMP; sodium transport; phosphodiesterase 5; endothelin-1
• ISSN: 1931-857X; 1522-1466
• DOI: 10.1152/ajprenal.00473.2015

In thick ascending limbs (THALs), nitric oxide (NO) decreases NaCl reabsorption via cGMP-mediated inhibition of Na-K-2Cl cotransporter (NKCC2). In angiotensin (ANG II)-induced hypertension, endothelin-1 (ET-1)-induced NO production by THALs is impaired. However, whether this alters NO's natriuretic effects and the mechanisms involved are unknown. In other cell types, ANG II augments phosphodiesterase 5 (PDE5)-mediated cGMP degradation. We hypothesized that NO-mediated inhibition of NKCC2 activity and stimulation of cGMP synthesis are blunted via PDE5 in ANG II-induced hypertension. Sprague-Dawley rats were infused with vehicle or ANG II (200 ng·kg ·min ) for 5 days. ET-1 reduced NKCC2 activity by 38 ± 13% ( < 0.05) in THALs from vehicle-treated rats but not from ANG II-hypertensive rats (Δ: -9 ± 13%). A NO donor yielded similar results as ET-1. In contrast, dibutyryl-cGMP significantly decreased NKCC2 activity in both vehicle-treated and ANG II-hypertensive rats (control: Δ-44 ± 15% vs. Δ-41 ± 10%). NO increased cGMP by 2.08 ± 0.36 fmol/μg protein in THALs from vehicle-treated rats but only 1.06 ± 0.25 fmol/μg protein in ANG II-hypertensive rats ( < 0.04). Vardenafil (25 nM), a PDE5 inhibitor, restored NO's ability to inhibit NKCC2 activity in THALs from ANG II-hypertensive rats (Δ: -60 ± 9%, < 0.003). Similarly, NO's stimulation of cGMP was also restored by vardenafil (vehicle-treated: 1.89 ± 0.71 vs. ANG II-hypertensive: 2.02 ± 0.32 fmol/μg protein). PDE5 expression did not differ between vehicle-treated and ANG II-hypertensive rats. We conclude that NO-induced inhibition of NKCC2 and increases in cGMP are blunted in ANG II-hypertensive rats due to PDE5 activation. Defects in the response of THALs to NO may enhance NaCl retention in ANG II-induced hypertension.