1. Attenuation of the effectiveness of antihypertensive therapy by non-steroidal antiinflammatory (NSAI) drugs has been attributed to inhibition of systemic or renal vasodilator prostaglandin synthesis, or a combination of both.

2. Indomethacin is a NSAI drug with both renal and extrarenal cyclo-oxygenase inhibition properties. Sulindac is a relatively selective cyclooxygenase inhibitor said not to affect urinary prostaglandin excretion.

3. This study examines the relative effect on blood pressure of 4 weeks' treatment, with indomethacin 25 mg three times daily and sulindac 200 mg twice daily, in a randomized placebo controlled trial in 26 hypertensive subjects.

4. In nine patients treated with indomethacin, supine blood pressure rose 11 mmHg systolic and 4 mmHg diastolic by the end of the first week, whereas nine subjects treated with sulindac showed a fall in blood pressure similar to the trend seen in placebo-treated subjects.

5. Indomethacin treatment inhibited renal cyclo-oxygenase with a 78% reduction in urinary prostaglandin E2 excretion and 89% suppression of plasma renin activity. Neither measurement was affected by sulindac. Extrarenal cyclo-oxygenase activity was inhibited by both indomethacin and sulindac with serum thromboxane B2 decreasing by 96% and 69% respectively.

6. The results suggest that the pressor effect of NSAI drugs is predominantly related to renal cyclo-oxygenase inhibition. The lack of effect of sulindac on blood pressure may make it a safer therapeutic option if NSAI drug therapy is necessary in the hypertensive patient.

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