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ROLE OF NITRIC OXIDE AND ENDOTHELIUM IN THE FLOW‐INDUCED DILATION OF RAT CORONARY ARTERIES UNDER TWO PRECONSTRICTION CONDITIONS
Author(s) -
Véquaud Philippe,
Pourageaud Fabrice,
Freslon JeanLouis
Publication year - 1999
Publication title -
clinical and experimental pharmacology and physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 103
eISSN - 1440-1681
pISSN - 0305-1870
DOI - 10.1046/j.1440-1681.1999.03061.x
Subject(s) - constriction , incubation , sodium nitroprusside , medicine , endothelium , cardiology , nitric oxide , contraction (grammar) , circulatory system , coronary arteries , artery , chemistry , anesthesia , anatomy , biochemistry
1. Pressure‐induced tone and flow‐induced dilations were studied in a rat perfused epicardial coronary artery mounted in an arteriograph. Spontaneous tone was assessed in arteries submitted either to 60 or 90 mmHg intraluminal pressure either under control conditions, after incubation with N G ‐nitro‐ L ‐arginine methyl ester ( L ‐NAME; 100 μmol/L) or after endothelial denudation. Flow‐induced dilation was quantified under these conditions in preparations either submitted to 60 mmHg and preconstricted with 10 μmol/L 5‐hydroxytryptamine (5‐HT) or exhibiting spontaneous tone at 90 mmHg. 2. Spontaneous tone was greater at 90 mmHg compared with tone obtained at 60 mmHg (21±2 vs 10±2% reduction of the fully dilated diameter after sodium nitroprusside incubation, respectively). Incubation with L ‐NAME or removal of the endothelium significantly increased spontaneous tone at both pressures compared with control. 3. In arteries submitted to 60 mmHg and preconstricted with 10 μmol/L 5‐HT, flow (0–800 μL/min) induced a continuous dilation (maximal value 63±4%). As a function of flow, shear stress first increased and then plateaued at values of approximately 76±6 dyn/cm 2 . After L ‐NAME incubation or endothelial denudation, the flow‐induced dilation was reduced to the same extent and was obtained for higher values of shear stress (172±14 and 150±14 dyn/cm 2 , respectively). 4. In arteries exhibiting spontaneous tone, starting flow led, first, to a constriction followed by a dilation up to 76±4% of the initial tone. Incubation with L ‐NAME greatly altered flow‐ induced dilation. Endothelium removal further reduced the dilation obtained for very high values of shear stress (up to 300 dyn/cm 2 ). 5. The present study shows that different patterns of vasodilation induced by flow can be observed, depending on the initial vasoconstrictor stimulus. In 5‐HT‐preconstricted arteries, flow‐induced dilation appears to be fully dependent on the synthesis and release of nitric oxide. In arteries with spontaneous tone, a vasoconstrictor substance could be released for low values of flow. Nitric oxide is mainly, but not exclusively, responsible for the vasodilation. For both experimental conditions, removal of the endothelium greatly reduced the response, but a dilation was still observed.