The aim of this study was to determine the effect of chronic crowding on the cardiovascular system of Wistar-Kyoto (WKY) rats. Rats were randomly divided into the control (480 cm2 per rat) or crowded (200 cm2 per rat) group for eight weeks. Body weight, blood pressure (BP), heart rate and plasma nitrate/nitrite levels of the crowded rats were not different from controls at the end of the experiment. Plasma corticosterone exhibited an increasing trend (5.7±1.8 vs. 12.6±3.7 ng/ml, p=0.08) while blood glucose was significantly reduced in the crowded rats in comparison with the controls. Nitric oxide (NO) synthase activity and nitrate/nitrite levels of the crowded rats were significantly elevated in the aorta by ∼80 % and ∼20 %, respectively, but unchanged in the left ventricle. Moreover, acetylcholine-induced relaxation was significantly increased in the crowded rats in both the femoral artery (61±5 % vs. 76±5 %, p<0.001) and mesenteric artery (51±6 % vs. 72±7 %, p<0.001). In conclusion, results suggest that chronic crowding may increase vasorelaxation and vascular NO production in normotensive rats. This may be considered as an adapting mechanism preventing the development of the stress-related elevation of BP. Additionally, results also suggest caution in the housing of rats because an inappropriate crowding may affect results of the experiment significantly., I. Bernátová, A. Púzserová, J. Navarová, Z. Csizmadiová, M. Zeman., and Obsahuje bibliografii a bibliografické odkazy