Inhalational anesthetics up-regulate constitutive and lipopolysaccharide-induced inducible nitric oxide synthase expression and activity

Nitric oxide (NO) is an important biological messenger involved in the regulation of blood vessel tone, neurotransmission, inflammatory responses, and host defenses. Inhalational anesthetics have been shown to inhibit the function of the NO signaling pathway in a variety of tissues. In addition, acute inhibition of the NO signaling pathway significantly reduced the required alveolar concentration of halothane or isoflurane for anesthesia, which suggests a role for the NO signaling pathway in mechanisms of anesthesia and consciousness. We now report that inhalational anesthetics affect gene expression of nitric oxide synthases (NOS) (EC 1.14.13.39), the enzymes that synthesize NO from L-arginine. Both halothane and isoflurane, at clinically relevant concentrations, significantly up-regulate the mRNA, protein, and activity level of NOS in lipopolysaccharide-treated macrophages (inducible NOS; type II NOS), and bovine pulmonary endothelial cells (endothelial constitutive NOS; type III NOS). This is a novel interaction between inhalational anesthetics and the NO signaling pathway and has wide- ranging implications for both clinical medicine and experimental biology.