iNOS expression in rat aorta is increased after spinal cord transection: a possible cause of orthostatic hypotension in man.

Orthostatic hypotension commonly occurs in persons with spinal cord injury (SCI), limiting rehabilitation and independence. Findings of increased production of nitric oxide (NO) by inducible nitric oxide synthase (iNOS) after exposure to simulated microgravity suggest that increased iNOS expression contributes to OH in persons with SCI. To test this possibility, male Wistar rats underwent surgical transection of the spinal cord (T10) or sham-SCI surgery followed by euthanasia 3, 7 or 14 days later. Expression in thoracic aortic of inducible (iNOS), endothelial (eNOS) and neuronal (nNOS) NOS was then determined. In SCI rats, expression of iNOS mRNA was decreased at 3 days, had returned to normal levels of expression at 7 days and was increased at 14 days post-SCI (1.8-fold). In contrast, levels of eNOS mRNA were increased at 3 days (1.4-fold), then declined over time reaching levels by day 14 that were reduced compared to sham-SCI (0.23-fold). There were no significant effects of SCI on nNOS expression. These findings suggest a possible role for increased iNOS expression in the pathogenesis of OH in persons with SCI.