Epidemiological studies indicate that arsenic exposure induces hypertension. We hypothesized that arsenate exposure modulates the contractility of vascular smooth muscle through the stress response. Intraperitoneal injection of sodium arsenate (15mg/kg) 16h before increased not only the blood pressure of rats but also the pressor response to preganglionic nerve stimulation (2 and 16Hz) or to bolus injection of vasopressin or phenylephrine in pithed rats as compared with the control rats. Exposure of rat aortic rings to 4mM sodium arsenate for 60min enhanced the contractile responses to KCl or phenylephrine as well as the HSP 70 expression 8h later, but did not affect the relaxation responses to acetylcholine, histamine, or sodium nitroprusside. These results suggest that brief exposure to arsenate is associated with enhanced contractility of vascular smooth muscle through the stress response.