When compared with conventional coronary artery bypass grafting with cardiopulmonary bypass, off-pump coronary artery bypass grafting achieved similar completeness of revascularization, similar in-hospital and 30-day outcomes, shorter length of stay, reduced transfusion requirement, and less myocardial injury.

We investigated the mechanisms of cerebral arteriolar dilation from topical acetylcholine and the nitrovasodilators, sodium nitroprusside, nitroglycerin, and nitric oxide, in anesthetized cats equipped with cranial windows for the observation of the cerebral microcirculation. Acetylcholine-mediated dilation was eliminated by topical methylene blue. This blockade was reversed by either topical superoxide dismutase, catalase, or deferoxamine. Nitroprusside- and nitric oxide-induced dilation were not affected by methylene blue. Vasodilation from the nitrovasodilators was significantly diminished by topical nitro blue tetrazolium, but acetylcholine-mediated dilation was unaffected by nitro blue tetrazolium. Neither methylene blue nor nitro blue tetrazolium affected dilation from topical 8-bromoguanosine 3',5'-cyclic monophosphate. These data show that methylene blue selectively blocks acetylcholine-mediated endothelium-dependent dilation by generating oxygen radicals. The mechanism involved is hydroxyl radical-mediated oxidation of endothelium-derived relaxing factor. Nitro blue tetrazolium selectively blocks dilation from the endothelium-independent nitrovasodilators. The endothelium-derived relaxing factor generated by acetylcholine in the cerebral microcirculation is not nitric oxide.

We review below published studies of endothelium-dependent vasodilation in vivo. Endothelium-dependent vasodilation has been demonstrated in conduit arteries in vivo and in the cerebral, coronary, mesenteric, and femoral vascular beds as well as in the microcirculation of the brain and the microcirculation of cremaster muscle. The available evidence, although not complete, strongly suggests that the endothellum-derived relaxing factor generated by acetylcholine in the cerebral microcirculation is a nitrosothiol. The endothelium-derived relaxing factor generated by bradykinin in this vascular bed is an oxygen radical generated in association with enhanced arachidonate metabolism via cyclooxygenase. In the microcirculation of skeletal muscle, on the other hand, the vasodilation from bradykinin is mediated partly by prostacycline and partly by an endothelium-derived relaxing factor similar to that generated by acetylcholine. Basal secretion of endothelium-derived relaxing factor is controversial in vivo but is usually present in vitro. On the other hand, it appears that endothelium-derived relaxing factor mediates flow-dependent vasodilation in both large vessels and in the microcirculation in vivo. The generation and release of endothelium-derived relaxing factor from endothelium may be abnormal in a variety of conditions including acute and chronic hypertension, atherosclerosis, and ischemia followed by reperfusion. Several mechanisms for these abnormalities have been identified. These include inability to generate endothelium-derived relaxing factor or destruction of endothelium-derived relaxing factor by oxidants after its release in the extracellular space. These abnormalities in endothelium-dependent relaxation may contribute to the vascular abnormalities in these conditions. (Hypertension 1990;16:371-386) T he discovery of endothelium-derived relaxing factor (EDRF) generated by acetylcholine 1 opened a new field of investigation into endothelium-derived vasoactive factors. It is now well established that a number of vasoactive agents indirectly induce vascular smooth muscle relaxation with ensuing vasodilation by acting on the endothelium to induce the generation and release of EDRFs. These substances are short-lived (Figure 1). Therefore, the final pathway for the vasodilation induced by EDRF is the same as that for the nitrodilators, which generate nitric oxide either spontaneously

Coronary artery disease (CAD) is one manifestation of ischemic heart disease, which is the leading cause of mortality in the world. In addition to preventive medical therapy and lifestyle changes, consideration of revascularization of obstructed arteries to reduce ischemia, alleviate angina, and improve quality of life is a mainstay of current practice. However, the benefits of different methods of revascularization in particular patient populations are debated. Percutaneous coronary intervention (PCI), which involves placement of intracoronary stents in most patients, is a less invasive procedure than coronary artery bypass graft (CABG) surgery. Although it is generally accepted that patients with single-vessel obstructive CAD are best treated with PCI, patients with multivessel CAD have a higher ischemia burden, a greater risk for developing recurrent ischemic events, and a higher mortality. It is in this patient population where the debate over revascularization with stents versus surgery continues.

We devised a technique for the in vivo assay of endothelium-derived relaxing factor (EDRF) from cerebral microvessels. We used anesthetized cats equipped with two cranial windows. One window (assay window) was subjected to muscarinic blockade with atropine to inhibit the direct effects of acetylcholine. EDRF production was induced in the donor window by superfusion with acetylcholine. The superfusate was then directed through the assay window with a delay of 6 s where it caused vasodilation equal to that seen in the donor window. The dilation was eliminated by lengthening the transit time from the donor to the assay window to greater than 2 min or by muscarinic blockade with atropine in the donor window but not by indomethacin in the donor window. It was also inhibited by hemoglobin and methylene blue or by selective damage to the endothelium of the vessels in the donor window with topical application of arachidonate or hydrogen peroxide. We conclude that the vasoactivity of the superfusate is due to EDRF released by acetylcholine from cerebral microvessels.