Vascular smooth muscle and nitric oxide.

Experiments were performed to investigate the production of endothelium-derived relaxing factor (EDRF or nitric oxide; NO) by vascular smooth muscle cells. The lumen of bovine pulmonary arteries were filled with Krebs-Henseleit solution (incubates). Both endothelium-intact and endothelium-deprived vessels were used. Incubate solutions from the lumen of generator vessels contained a significant amount of nitric oxide (NO). Although the NO concentration was higher in incubates from endothelium-intact vessels, endothelium-deprived vessels also produced NO. The length of incubation did not influence the amount of nitric oxide released. Endothelium-deprived pulmonary arteries also generated NO as detected by chemiluminescence. The amount produced however was not sufficient to relax endothelium-deprived detector vessels in superfusion bioassay experiments. Samples from Krebs-Henseleit (K-H) solution surrounding the preparation (bathing solution) contained NO values which were also significantly higher than the control. Nitric oxide found in the bathing solution also appeared to originate from endothelium and vascular smooth muscle. Oxyhemoglobin attenuated NO signals. The results demonstrate that nitric oxide is released by vascular smooth muscle cells as well as by endothelium. However, the amount of NO released by muscle is insufficient to relax endothelium-deprived vascular preparations.