The contribution of carbon monoxide to vascular tonus.

Objective: The aim of this descriptive study was to examine the contribution of CO in the maintenance of vascular tonus in different organs and different vessel segments; the underlying mechanism of CO-induced vasodilation was investigated. Methods: Sixty Wistar albino rats, aged 6-8 months, were used in this study. Response to CO by isolated arteries from the thoracic and abdominal aorta and mesenteric, renal, gastrocnemius, and gracilis muscles as well as heart, lung, and brain vascular beds was endogenously and exogenously studied using organ baths or myograph. In addition, HO-2 protein expression was assessed using Western blot analysis in isolated vessel segments. Results: Although CO was shown to contribute to the regulation of vascular tonus in all feed arteries except those of the gracilis vascular bed, no effect was observed in the resistance arteries, with the sole exception of the pial artery. No relationship between HO-2 protein level and CO contribution to endogenous vascular tonus was observed. Conclusions: While the vasodilator effect of CO in vessels smaller than 600 mu m in diameter was found to be mediated via potassium channels, in vessels larger than 600 mu m in diameter, the effect was through both the potassium channels and the cGMP pathway.