Captopril increases the affinity of bradykinin receptor binding sites in bovine coronary arterial endothelial cells.

In a radioligand binding study using bovine coronary artery endothelial cell membranes, captopril changed a single bradykinin (BK) binding site (Kd= 1.77 nM, Bmax = 60.2 fmol/mg protein) to high-(Kd = 0.68 pM, Bmax= 17.7 fmol/mg protein) and low-(Kd= 1.00 nM, Bmax = 72.5 fmol/mg protein) affinity binding sites. This effect was reversed by GppNHp. Captopril also enhanced BK-induced endothelium-dependent relaxation in saponin-treated coronary rings, and GppNHp partially suppressed this enhancement. These results suggest that captopril may affect BK receptors that couple to G-proteins.