The study investigates the role of endothelium-derived nitric oxide (NO) in blood pressure regulation using anesthetized rabbits and the specific inhibitor Nω-monomethyl-L-arginine (L-NMMA). L-NMMA, but not its d-enantiomer, induced a dose-dependent increase in mean systemic arterial blood pressure, which was reversed by L-arginine. L-NMMA also inhibited the hypotensive action of acetylcholine (ACh) without affecting glyceryl trinitrate (nGlo). These effects were associated with a significant inhibition of NO release from perfused aortic segments ex vivo, which was reversed by infusing L-arginine. The results suggest that NO formation from L-arginine by vascular endothelium plays a crucial role in blood pressure regulation and the hypotensive actions of ACh. The study provides the first evidence that NO formation contributes to blood pressure regulation and highlights the potential importance of NO in hypertension.The study investigates the role of endothelium-derived nitric oxide (NO) in blood pressure regulation using anesthetized rabbits and the specific inhibitor Nω-monomethyl-L-arginine (L-NMMA). L-NMMA, but not its d-enantiomer, induced a dose-dependent increase in mean systemic arterial blood pressure, which was reversed by L-arginine. L-NMMA also inhibited the hypotensive action of acetylcholine (ACh) without affecting glyceryl trinitrate (nGlo). These effects were associated with a significant inhibition of NO release from perfused aortic segments ex vivo, which was reversed by infusing L-arginine. The results suggest that NO formation from L-arginine by vascular endothelium plays a crucial role in blood pressure regulation and the hypotensive actions of ACh. The study provides the first evidence that NO formation contributes to blood pressure regulation and highlights the potential importance of NO in hypertension.