Ambient particulate matter induces relaxation of rat aortic rings in vitro

Epidemiological studies have shown an association between ambient levels of particulate matter (PM) and increased mortality from cardiovascular diseas es. However, the underlying mechanisms are still not clear. We hypothesised that PM, when translocated after inhalation, could affect vascular smooth muscle function. Therefore, total suspended particulate matter (TSP) was sa mpled and investigated for its ability to affect aortic muscle contraction. Both TSP and TSP supernatant (TSP-sup) induced a concentration-dependent r elaxation of phenylephrine (PE)-precontracted aortic rings. Relaxation indu ced by 300 mug/ml TSP was 51.5 +/- 3.1% of total contraction. At 60 and 100 mug/ml, relaxation induced by TSP was significantly higher compared to TSP -sup. Ultrafine TiO2, used as a model to investigate the role of ultrafine particles, did not show an effect. Soluble iron, present in TSP suspensions , seems not to be involved, as chelating with deferoxamine did not affect T SP-induced relaxation. However, TSP effects were inhibited by Trolox, sugge sting a role of oxidants. Nudation of aortic rings showed that effects of T SP were only partly endothelium-dependent, while preincubation with L-NAME increased TSP-induced relaxation. From these data, we conclude that both th e particle core and soluble components of TSP can affect the smooth muscle function, leading to changes in the vascular contractile response.