ABSTRACT Red wine vasodilates rat aortae, an effect attributed to polyphenolic compounds. Cranberry juice (CBJ) is also rich in polyphenols. We determined that CBJ has vasorelaxing properties similar to those of red wine. Rat aortic rings cleaned in Krebs buffer, pH 7.4, bubbled with 95% O(2) and 5% CO(2) were recovered for 30 minutes at 37 degrees C under 2.0 g tension. After phenylephrine (PE, 100 mumol/L) contraction, acetylcholine (3 mumol/L)-induced relaxation of intact vessel was significantly higher than in denuded vessels (59.1 +/- 0.27% versus 10.1 +/- 0.09% of the maximal PE contraction; P .003). After a second PE contraction, a 1:100 dilution of CBJ was added. Intact rings were vasodilated by CBJ with 56.7 +/- 0.26% relaxation, compared to denuded rings with 8.9 +/- 0.06% relaxation (P .002). Addition of L-NAME reversed CBJ-induced vasorelaxation in intact vessels with 0.54 +/- 0.34 g compared to 0.04 +/- 0.04 g in denuded vessels (P .007). Subsequent addition of L-arginine resulted in a return of vasodilation in intact vessels. Additionally, CBJ infusion at a 1:100 dilution of estimated blood volume resulted in a 16% reduction of mean arterial blood pressure in anesthetized rats. This study suggests that, like red wine, CBJ has the capacity to exert in vitro and in vivo vasodilatory effects.