Previous studies showed that pertussis toxin (PT) decreased agonist-induced contractions of isolated rat small mesenteric resistance arteries independently from endothelium, nitric oxide-synthase or intracellular calcium concentrations. In this study, it was investigated if the PT-induced decreased contractile properties of small mesenteric resistance arteries could be a consequence of a PT-induced vascular and/or smooth muscle cell injury, leading to loss of contractile functionality. Male Wistar rats were treated with PT (30 microg/kg, intravenously) and sections of isolated small mesenteric resistance arteries were investigated with light- and electron microscopy. Light microscopic investigation of cross-sectioned small mesenteric resistance arteries of control animals clearly showed a contracted phase, while PT-pretreated animals showed a relaxed smooth inner surface of the vessel, indicating a vasodilated state. Electron microscopic investigation showed that PT-pretreatment neither induced vascular lesions nor caused morphological or numerical changes in cell organelles such as contractile elements of vascular smooth muscle cells. In conclusion, the PT-induced decreased contractile properties of isolated rat small resistance arteries are not caused by a PT-induced vascular and/or smooth muscle cell injury.