Captopril is a potent hypotensive agent whose efficacy has hitherto been attributed to its ability to alter either angiotensin II formation or kinin degradation. Our purpose was to examine captopril's acute effect on prostaglandin production, because changes in neither the renin-angiotensin nor the kallikrein-kinin systems appear adequate to account for the fall in arterial pressure. The plasma levels of angiotensin II, kinins, and prostaglandins were determined in response to increasing doses (5, 12.5, and 25 mg) of captopril and these responses were compared with the change in arterial pressure observed in nine supine normal male subjects studied on both a high (200 meq) and low (10 meq) sodium intake.

Captopril significantly (P < 0.01) increased the levels of the 13,14-dihydro-15-keto metabolite of prostaglandin E₂ (PGE₂-M), a potent vasodilator, with similar responses being observed on both a high and a low sodium intake. No significant changes in the plasma levels of 6-keto-prostaglandin F ₁α, or thromboxane B₂, the stable products of prostacyclin and thromboxane A₂, respectively, occurred.

The depressor response to captopril correlated with the change in PGE₂-M (r = 0.52, t = 5.44, P < 0.0001). On the other hand, although significant (P < 0.02) decrements in angiotensin II and increments in plasma kinins accompanied the hypotensive response in sodium-restricted subjects, in sodium-loaded subjects where the renin-angiotensin system was suppressed, no change in angiotensin II, and only a modest change in kinins was noted, even though significant (P < 0.01) decrements in diastolic blood pressure occurred (−10±2 mm Hg).

Thus, changes in depressor prostaglandin production can better account for the hypotensive response to captopril, thereby extending to yet another vasoactive system an influence by this class of drugs and providing a new approach to dissecting the abnormality in the control of vascular tone in patients with hypertension.