We hypothesized that microvascular reactivity is impaired after particulate matter (PM) exposure in rat coronary arterioles. Rats were exposed to filtered air (control), fine PM, or ultrafine (UF) PM via inhalation at concentrations relevant to ambient air pollution (10 and 67 mug measured pulmonary deposition). Coronary arterioles were cannulated and responses to flow, acetylcho-line (ACh), endothelin (ET) and dea-NONOate were assessed. Exposure to fine and UF PM impaired flow-dependent dilation, but not ACh responsiveness. Vascular smooth muscle NO sensitivity and vasoconstriction to ET were decreased after exposure to UF PM, but not fine PM. These results suggest that UF PM exposure causes more coronary microvascular dysfunction than fine PM and could contribute to cardiac events associated with PM exposure.
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