title: Shear stress increases nitric oxide production in thick ascending limbs.
abstract: We showed that luminal flow stimulates nitric oxide (NO) production in thick ascending limbs. Ion delivery, stretch, pressure, and shear stress all increase when flow is enhanced. We hypothesized that shear stress stimulates NO in thick ascending limbs, whereas stretch, pressure, and ion delivery do not. We measured NO in isolated, perfused rat thick ascending limbs using the NO-sensitive dye DAF FM-DA. NO production rose from 21 ± 7 to 58 ± 12 AU/min (P < 0.02; n = 7) when we increased luminal flow from 0 to 20 nl/min, but dropped to 16 ± 8 AU/min (P < 0.02; n = 7) 10 min after flow was stopped. Flow did not increase NO in tubules from mice lacking NO synthase 3 (NOS 3). Flow stimulated NO production by the same extent in tubules perfused with ion-free solution and physiological saline (20 ± 7 vs. 24 ± 6 AU/min; n = 7). Increasing stretch while reducing shear stress and pressure lowered NO generation from 42 ± 9 to 17 ± 6 AU/min (P < 0.03; n = 6). In the absence of shear stress, increasing pressure and stretch had no effect on NO production (2 ± 8 vs. 8 ± 8 AU/min; n = 6). Similar results were obtained in the presence of tempol (100 μmol/l), a O(2)(-) scavenger. Primary cultures of thick ascending limb cells subjected to shear stresses of 0.02 and 0.55 dyne/cm(2) produced NO at rates of 55 ± 10 and 315 ± 93 AU/s, respectively (P < 0.002; n = 7). Pretreatment with the NOS inhibitor l-NAME (5 mmol/l) blocked the shear stress-induced increase in NO production. We concluded that shear stress rather than pressure, stretch, or ion delivery mediates flow-induced stimulation of NO by NOS 3 in thick ascending limbs.
authors: Hypertension and Vascular Research Div., Dept. of Internal Medicine, Henry Ford Hospital, 2799 West Grand Blvd., Detroit, MI 48202, USA.
authors: Pablo D
authors: PD
authors: Cabral
authors: Nancy J
authors: NJ
authors: Hong
authors: Jeffrey L
authors: JL
authors: Garvin
mesh_terms: D000818:Animals; D048429:Cell Size; D017364:Collagenases / Q000737:chemistry / Q000494:pharmacology; D003497:Cyclic N-Oxides / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D016166:Free Radical Scavengers / Q000494:pharmacology; D007684:Kidney Tubules / Q000378:metabolism; D008138:Loop of Henle / Q000201:enzymology / Q000378:metabolism* / Q000502:physiology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009569:Nitric Oxide / Q000096:biosynthesis*; D052250:Nitric Oxide Synthase Type III / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D011312:Pressure; D051381:Rats; D017207:Rats, Sprague-Dawley; D017382:Reactive Oxygen Species / Q000378:metabolism; D012965:Sodium Chloride / Q000378:metabolism; D013113:Spin Labels; D013314:Stress, Mechanical
chemical_list: D003497:Cyclic N-Oxides; D004791:Enzyme Inhibitors; D016166:Free Radical Scavengers; D017382:Reactive Oxygen Species; D013113:Spin Labels; D009569:Nitric Oxide; D012965:Sodium Chloride; D052250:Nitric Oxide Synthase Type III; C496315:Nos3 protein, mouse; C496316:Nos3 protein, rat; D017364:Collagenases; C001803:tempol; D019331:NG-Nitroarginine Methyl Ester