Taurine plays an important role in the modulation of cardiovascular function by acting not only within the brain but also within peripheral tissues. We found that IV injection of taurine to male rats caused hypotension and tachycardia. A single injection of taurine significantly lowered the systolic, diastolic, and mean arterial blood pressure in freely moving Long-Evans control rats. We further confirm the vasoactive properties of taurine using isolated aortic ring preparations. Mechanical responses of circular aortic rings to pharmacological agents were measured by an isometric force transducer and amplifier. We found that bath application of taurine to the aortic rings caused vasodilation which was blocked by picrotoxin. Interestingly, picrotoxin alone induced a constriction of the aortic ring in the absence of exogenously added taurine, suggesting a tonic activation of GABA(A)receptors by circulating either taurine or GABA. Additionally, we found that the endothelial cells express high levels of taurine transporters and GABA(A)receptors. We have previously shown that taurine activates GABA(A)receptors and thus we suggest that the functional implication of GABA(A)receptor activation is the relaxation of the arterial muscularis, vasodilation, and a decrease in blood pressure. Interestingly however, the effects of acute taurine injection were very different than chronic supplementation of taurine. When rats were supplemented taurine (0.05%, 4 weeks) in their drinking water, taurine has significant hypertensive properties. The increase in blood pressure was observed however only in females; males supplemented with taurine did not show an increase in systolic, diastolic, or mean arterial pressure. In both genders however, taurine supplementation caused a significant tachycardia. Thus, we suggest that acute administration of taurine may be beneficial to lowering blood pressure. However, our data indicate that supplementation of taurine to females caused a significant increase in blood pressure. The effect of taurine supplementation on hypertensive rats remains to be seen.