Cyclooxygenase inhibition reduces blood pressure elevation and vascular reactivity dysfunction caused by inhibition of nitric oxide synthase in rats.

In the present study we investigated the role of cyclooxygenase (COX)-dependent vasoconstrictors in the hypertension and altered vascular reactivity following prolonged nitric oxide (NO) synthase inhibition. Male Wistar rats (250-270 g) were divided into four groups and treated for 7 days with Placebo (control), L-NAME (48 mg/kg/day), indomethacin (4 mg/kg/day) and L-NAME in combination with indomethacin. L-NAME treatment induced arterial hypertension, in vitro aortic hyperresponsiveness to phenylephrine, impaired vasodilatory response to acetylcholine and no significant change in response to sodium nitroprusside. Indomethacin co-treatment partially prevented blood pressure elevation, restored responsiveness to phenylephrine and improved sensitivity to acetylcholine. Indomethacin treatment alone did not modify blood pressure and aortic vascular reactivity. Both enhanced phenylphrine-induced contraction and impaired acetylcholine-evoked vasodilation induced by acute NO synthase inhibition with L-NAME (10(-4) M) in normal rat aortas were not modified by indomethacin (10(-5) M). These results are consistent with the hypothesis that constricting factors, which arise from the COX pathway, contribute to hypertension and altered vascular reactivity following continued inhibition of NO synthase.