Evidence for nitric oxide mediation of contractile activity in isolated strips of the human Fallopian tube

Endogenously produced nitric oxide (NO) induces relaxation in smooth muscle in various organs. The purpose of this study was to investigate whether a NO-mediated relaxation system exists in the human Fallopian tube. To study contractility, the isthmic portion of the tube was obtained from 23 fertile women during operations due to benign non-tubal diseases. Tubal smooth muscle strips were mounted in tissue chambers containing HEPES buffer and connected to a Grass transducer for the isometric registration of contractile activity. By adding L-arginine (the substrate for NO synthesis) or N-nitro-L-arginine methyl ester (L-NAME; an inhibitor of NO synthesis) to the tissue chambers, changes in tubal contractility were monitored. The addition of L-NAME caused increased tubal contractility, while L-arginine, after an initial transient increase in tonus, caused relaxation of the strips. Using immunohistochemistry, NO synthase, the enzyme that catalyses the production of NO from L-arginine, was identified in tubal tissue cells. These results indicate that a NO-dependent relaxation system exists in the Fallopian tube and that NO may play a role as a mediator of tubal contractility.