ANGIOTENSIN CONVERTING ENZYME INHIBITION ACTIVITY OF DAIDZEIN

Abstract

Daidzein produces antihypertensive and beneficial cardiovascular effects, although the mechanisms for these effects are not known. We examined whether genistein inhibits the in vivo responses to angiotensin I or enhances the responses to bradykinin in anaesthetized rats as a result of angiotensin-converting enzyme inhibition. We have also studied the in vitro effects produced by genistein on the angiotensin-converting enzyme activity. We measured the changes in systemic arterial pressure induced by angiotensin I in doses of 0.05 to 10 µg/kg, by angiotensin II in doses of 0.025 to 5 µg/kg, and to bradykinin in doses of 0.03 to 10 µg/kg in anaesthetized rats pretreated with vehicle (controls), or a single i.v. dose of daidzein 25 mg/kg, or a single i.v. dose of enalapril 2 mg/kg. Plasma angiotensin-converting enzyme activity was determined in controls and daidzein-treated rats using a fluorometric method. The effects of genistein (3–300 µmol/l) on in vitro angiotensin-converting enzyme activity were assessed by adding daidzein to plasma samples and measuring angiotensin-converting enzyme activity. We found significant lower angiotensin-converting enzyme activity in plasma samples from rats pretreated with daidzein compared with those found in the control group (84.23±7.4 his-leu nmol/min/ml and 100.45±9.2 his-leu nmol/min/ml, respectively; P = 0.01). The incubation of daidzein with plasma samples showed that daidzein decreased the angiotensin-converting enzyme activity in plasma in a concentration-dependent manner (P=0.01). These findings indicate that daidzein inhibits the angiotensin-converting enzyme in vivo and in vitro and may explain, at least in part, the antihypertensive and beneficial vascular effects produced by daidzein.

Keyword: Angiotensin, Daidzein, Bradykinin, Arterial pressure.