Angiotensin II‐Dependent Hypertension Blunts Endothelin‐1‐Induced NO Production in Thick Ascending Limbs

Thick ascending limbs (THALs) absorb 25% of the filtered NaCl load. Endothelin‐1 (ET‐1) inhibits THAL NaCl absorption by stimulating NO production. We showed that NaCl absorption by THALs is enhanced during angiotensin II (Ang II)‐induced hypertension. We hypothesized that Ang II‐induced hypertension blunts ET‐1‐stimulated NO production in THALs. To test our hypothesis, male Sprague‐Dawley rats were infused with vehicle or Ang II 200 ng/kg/min. At day 5, NO production by THALs was measured by fluorescence microscopy using DAF‐2FM. In normotensive rats, ET‐1 increased NO production from 0.21± 0.05 to 0.37 ± 0.03 FU/min ( p <0.01), but in Ang II‐hypertensive rats NO production did not change (control: 0.21 ± 0.06 vs ET‐1: 0.18± 0.05 FU/min). ET‐1 stimulates NO production via PI3K. PI3K actions are mediated by phosphatidylinositol 3,4,5‐trisphosphate (PIP3). We next investigated whether the blunted response was due to defects downstream PI3K. PIP3 (5 μM) increased NO production to the same extent in normotensive (from 0.16 ± 0.03 to 0.41 ± 0.05 FU/min, p <0.03) and in hypertensive rats (from 0.17 ± 0.07 to 0.51 ± 0.11 FU/min, p <0.01). These data indicate that in Ang II‐induced hypertension, ET‐1‐induced NO production is blunted in THALs and that this defect resides upstream of PIP3. Impaired ET‐1‐induced NO production in THALs could lead to the enhanced NaCl reabsorption observed in Ang II‐induced hypertension.