Impulse flow in sympathetic efferents of the abdominal aortic nerve after intrathecal administration of the substrate and inhibitor of nitric oxide synthase.

Experiments were performed on rats anesthetized with urethane and nembutal. Intrathecal administration of a nitric oxide inhibitor L-NAME (60 mg) into the cerebrospinal fluid of the thoracic spinal cord was followed by a 40-45% decrease in tonic activity of efferent fibers of the abdominal aortic nerves. L-NAME reduced a reflex increase in the rate of efferent impulses, which was induced by tetanic stimulation of afferent C-fibers in the mesenteric nerve. Administration of L-arginine into the cerebrospinal fluid of the spinal cord (80 mg/20 ml) was accompanied a long-term increase in tonic activity of efferent fibers of the abdominal aortic nerves (by 15-20%). These changes reflect a prolonged activating effect of L-arginine on sympathetic structures.