Stresses such as heat shock, ischemia, and irradiation have been known to induce heat shock proteins in various tissues. We investigated the effects of heat shock on the vascular contractility by using isolated rat aorta. Rat thoracic aortic rings were mounted in an organ bath maintained at 37 degrees C. For heat shock, aortic ring preparations were exposed to 42 degrees C for either 15 or 45 min (heat shock group), whereas the control group was left at 37 degrees C. Eight hours after heat shock, aortic ring preparations were subjected to contractions with high K(+) membrane-depolarizing solution. After functional study, tissues were frozen for measurement of heat shock protein 70 (HSP70). Heat shock not only increased the expression of HSP70 in the rat aorta, but also augmented contractions to KCl whether endothelium was present or denuded. Short exposure of tissues to 42 degrees C for 15 min did not work either. These results suggest that heat shock increases vascular contractility in isolated aortic strips.