Inhibition of fibrin-induced neurogenic pulmonary edema by previous unilateral left-vagotomy correlates with increased levels of brain nitric oxide synthase in the nucleus tractus solitarii of rats

In the course of investigations on mechanisms underlying development of neurogenic pulmonary edema (NPE), we have evaluated effects of nitric oxide (NO) in the central nervous system on incidence and severity in the fibrin-induced pulmonary edema model. Rats were left-unilaterally vagotomized 1, 2 and 4 weeks before injections of fibrinogen and thrombin into the cisterna magna, after cutting the right vagus nerve, grouped as LV1W, LV2W or LV4W, respectively. The brain NO synthase (NOS) mRNA level in the left medulla oblongata was elevated in the LV2W group, compared to the control, but decreased in the LV4W rats. Incidences of pulmonary edema were 100% in the control group, decreasing to 78% in LV1W group, 17% in LV2W group, and back to 72% in LV4W group. The lung water ratio, a parameter of severity, demonstrated a similar pattern of change as the incidence. The lowered incidence and severity obtained in the LV2W group were reversed by intracisternal injection of N^ω-nitro-L-arginine methyl ester (L-NAME). From these results, we propose that an increase in nitric oxide, possibly in the nucleus tractus solitarius 2 weeks after left vagotomy, may have an inhibitory action on the development of neurogenic pulmonary edema in rats.