Effects of hypoxia/reoxygenation on aortic vasoconstrictor responsiveness.
The purpose of the present study was to assess the effects of hypoxia/reoxygenation (H/R) on vasoconstrictor effectiveness, in vitro. Aortic rings were obtained from rats and placed on isometric force transducers in oxygenated Krebs buffer (95% O2/5% CO2, PO2 > 500 torr). Cumulative concentration/effect relationships to norepinephrine, G-protein activation by AlICl3/NaF, depolarization by KCl or BayK-8644, mobilization of intracellular calcium by caffeine, and protein kinase C activation by l-indolactam were evaluated. Hypoxia (PO2 < 5 torr) was induced by rapidly bubbling the Krebs buffer with 95% N2/5% CO2 for 15 min. Vessel rings were reoxygenated for 30 min and concentration/effect relationships reevaluated. The dissociation constant (KA) for norepinephrine was also determined. The pD2 for maximal norepinephrine responsiveness decreased from 7.7 to 7.3 following H/R. Maximal tension generation was significantly decreased following H/R. Endothelium denudation or nitric oxide synthesis inhibition did not prevent the right shift in norepinephrine concentration/effect relationship caused by H/R. The combination of superoxide dismutase and catalase prevented the dextral shift in the concentration/effect curve. The dissociation constant for norepinephrine increased from 0.16 to 0.32 microM following H/R, suggesting decreased affinity of adrenergic receptor. H/R did not alter AlCl3/NaF, KCl, BayK-8644 or l-indolactam-induced vasoconstriction. Caffeine-induced vasoconstriction was significantly impaired following H/R, suggesting that release of calcium from the sarcoplasmic reticulum is compromised. These results suggest that H/R leads to an endothelium independent, oxidant-mediated decrease in vascular norepinephrine responsiveness that may be related to defects in the mobilization of intracellular calcium from the sarcoplasmic reticulum pool.
Department of Physiology and Biophysics, Louisiana State University Medical Center, Shreveport, USA.
H
H
Gao
R J
RJ
Korthuis
J N
JN
Benoit
D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects / Q000503:physiopathology; D002110:Caffeine / Q000494:pharmacology; D002374:Catalase / Q000494:pharmacology; D004730:Endothelium, Vascular / Q000503:physiopathology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005609:Free Radicals / Q000378:metabolism; D000860:Hypoxia / Q000503:physiopathology*; D066298:In Vitro Techniques; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000503:physiopathology; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D009638:Norepinephrine / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D017382:Reactive Oxygen Species / Q000378:metabolism; D015427:Reperfusion Injury / Q000503:physiopathology; D013482:Superoxide Dismutase / Q000494:pharmacology; D014661:Vasoconstriction / Q000187:drug effects / Q000502:physiology*
D004791:Enzyme Inhibitors; D005609:Free Radicals; D017382:Reactive Oxygen Species; D002110:Caffeine; D002374:Catalase; D019001:Nitric Oxide Synthase; D013482:Superoxide Dismutase; D019331:NG-Nitroarginine Methyl Ester; D009638:Norepinephrine