Role of vascular heme oxygenase in reduced myogenic reactivity following chronic hypoxia.
OBJECTIVE
Exposure to chronic hypoxia (CH) results in a persistent endothelium-dependent vascular smooth muscle hyperpolarization that diminishes vasoconstrictor reactivity. Experiments were performed to test the hypothesis that products of both cytochrome P450 epoxygenase (CYP) and heme oxygenase (HO) are required for the persistent diminished myogenic reactivity following CH.


METHODS
The authors examined myogenic responses of mesenteric arteries isolated from control and CH (48 h; P(B) = 380 mmHg) rats in the presence of a HO inhibitor (zinc protoporphyrin IX; ZnPPIX) or combined HO and CYP epoxygenase inhibition (sulfaphenazole). Arteries were isolated and cannulated and the vascular smooth muscle was loaded with the Ca2+ indicator Fura-2.


RESULTS
Control vessels maintained their internal diameter in response to step increases in intraluminal pressure, whereas arteries from CH animals passively distended. ZnPPIX augmented myogenic reactivity and [Ca2+] in arteries from CH animals. Combined administration of sulfaphenazole and ZnPPIX did not have an additional effect compared to ZnPPIX alone. Myogenic reactivity in control vessels was not altered by ZnPPIX or ZnPPIX + sulfaphenazole.


CONCLUSIONS
HO appears to play a role in regulating myogenic reactivity following CH. Furthermore, these data suggest that products of HO and CYP are both required for the observed attenuation in vasoreactivity following CH.
Naik
Jay S
JS
Vascular Physiology Group, Department of Cell Biology and Physiology, University of New Mexico Health Sciences Center, Albuquerque, New Mexico, USA.
Walker
Benjimen R
BR
D000818:Animals; D000890:Anti-Infective Agents / Q000008:administration & dosage; D002908:Chronic Disease; D000090762:Cytochrome P-450 CYP2J2; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000008:administration & dosage; D006419:Heme Oxygenase (Decyclizing) / Q000378:metabolism*; D000860:Hypoxia / Q000201:enzymology* / Q000473:pathology; D066298:In Vitro Techniques; D008297:Male; D008638:Mesenteric Arteries / Q000201:enzymology / Q000473:pathology; D009131:Muscle, Smooth, Vascular / Q000201:enzymology* / Q000473:pathology; D010105:Oxygenases / Q000378:metabolism*; D017319:Photosensitizing Agents / Q000008:administration & dosage; D011524:Protoporphyrins / Q000008:administration & dosage; D051381:Rats; D017207:Rats, Sprague-Dawley; D013426:Sulfaphenazole / Q000008:administration & dosage; D014661:Vasoconstriction
D000890:Anti-Infective Agents; D004791:Enzyme Inhibitors; D017319:Photosensitizing Agents; D011524:Protoporphyrins; D013426:Sulfaphenazole; D003577:Cytochrome P-450 Enzyme System; C028025:protoporphyrin IX; D010105:Oxygenases; D000090762:Cytochrome P-450 CYP2J2; D006419:Heme Oxygenase (Decyclizing)