Urinary excretion of prostacyclin and thromboxane A2 metabolites after angiotensin converting enzyme inhibition in hypertensive patients.

The contribution, if any, of various prostaglandins to the antihypertensive effects of angiotensin converting enzyme inhibitors (ACEI) is controversial. We studied the effect of the ACEI captopril (CAP) on the urinary excretion of 6-keto-PGF2 alpha (6-KF), the major metabolite of the vasodilatory prostaglandin, prostacyclin, and thromboxane B2 (TxB2), the stable metabolite of the vasoconstrictor TxA2, in 8 patients with essential hypertension after placebo, two weeks of CAP 25 mg t.i.d. alone, and the same dose of CAP in combination with hydrochlorothiazide (HCTZ) 50 mg/day. Mean 6-KF and TxB2 (nmol/8 hr post-dosing, respectively) did not differ significantly with any treatment; the mean ratio of 6-KF/TxB2 was also unchanged. Likewise, the excretion of these prostaglandins was also evaluated after placebo, the ACEI enalapril (ENA) (5 or 10 mg/day), and the combination of ENA and HCTZ in another group of 8 patients with essential hypertension. Mean 6-KF and TxB2 (nmol/24 hr post-dosing, respectively) showed no significant treatment-related differences; the mean ratio was again unchanged. No correlation existed between the magnitude of blood pressure responses with any treatment and either 6-KF or TxB2 excretion. Thus, the antihypertensive action of ACEI, alone or in combination with HCTZ, does not appear to involve alterations in these vasoactive prostaglandins.