Effect of genistein on cardiovascular responses to angiotensin II in conscious unrestrained rats

Soybeans contain genistein, a phytoestrogen that may have beneficial effect s in coronary artery disease, osteoporosis, and breast cancer. In vitro stu dies demonstrated that genistein reduced vascular smooth muscle contraction s to angiotensin II. We tested the hypothesis that genistein attenuates the overall cardiovascular responses to angiotensin II via nongenomic mechanis ms in conscious rats. Mean arterial blood pressure (MAP) was recorded from conscious unrestrained Sprague-Dawley rats (n = 26) approximately 48 hours after surgery. Cumulative dose response curves to angiotensin II (10-200 ng /kg/min) were constructed before and after i.v. treatment with genistein gi ven as a single bolus dose of 160 mug/kg or 1500 mug/kg, or as a loading do se of 160 mug/kg followed by an infusion at a rate of 20 mug/kg Angiotensin II infusions were associated with graded increases in arterial pressure ra nging between 0 +/- 1 and 35 +/- 4 mm Hg. These presser responses were acco mpanied by significant dose-dependent decreases in heart rate. None of the genistein treatment regimens significantly affected the presser responses t o angiotensin II. Accordingly, we conclude that short-term i.v, treatment w ith genistein does not depress presser responsiveness to angiotensin II.