(Hypertension. 2001;38:833.)
© 2001 American Heart Association, Inc.
Scientific Contributions |
From the Centre for Clinical Pharmacology, University College London, The Rayne Institute, London, United Kingdom.
Correspondence to Dr Amrita Ahluwalia, Centre for Clinical Pharmacology, University College London, The Rayne Institute, 5 University St, London, United Kingdom WC1E 6JJ. E-mail a.ahluwalia{at}ucl.ac.uk
Abstract Myogenic tone is an important determinant of vascular tone and blood flow in small resistance arteries of certain vascular beds. The role of the endothelium in myogenic responses is unclear. We hypothesized that endothelium-derived NO release modulates myogenic constriction in small resistance arteries and that mesenteric small arteries from mice with targeted disruption of the gene for endothelial NO synthase (eNOS) (knockout mice) demonstrate greater myogenic tone than do wild-type mice. Third-order mesenteric arteries (
200 µm) were isolated and mounted in a pressure myograph. Internal diameter was recorded over a pressure range of 10 to 80 mm Hg. Removal of the endothelium significantly (P<0.05) enhanced the magnitude of myogenic constriction in wild-type mice. Similarly, pretreatment of arteries with NG-nitro-L-arginine methyl ester (L-NAME; 300 µmol/L) produced a comparable significant (P<0.05) increase in myogenic tone, whereas indomethacin (5 µmol/L) had no effect. eNOS knockout arteries also exhibited myogenic constriction. Neither L-NAME nor indomethacin had any effect on myogenic tone in the arteries of eNOS knockout mice. However, blockade of potential endothelium-derived hyperpolarizing factorlike mechanisms via inhibition of K+ flux using either apamin (100 nmol/L) with charybdotoxin (100 nmol/L), Ba2+ (30 µmol/L) with ouabain (1 mmol/L), or 18
-glycyrrhetinic acid (100 µmol/L) significantly (P<0.01) enhanced myogenic constriction. This study demonstrates that basal endothelium-derived NO modulates myogenic tone in mesenteric small arteries of wild-type mice. However, eNOS knockout arteries display normal myogenic responsiveness despite the absence of basal NO activity. The data suggest that this compensatory effect is due to the activity of an endothelium-derived hyperpolarizing factor to normalize vascular tone.
Key Words: nitric oxide endothelium mice nitric oxide synthase autoregulation
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