Expression of inducible nitric oxide synthase in rats following subarachnoid hemorrhage

The possible expression of the inducible isoform of nitric oxide synthase (iNOS) was examined in a rat model of subarachnoid hemorrhage (SAH). Subarachnoid hemorrhage was induced by the injection of autologous blood into the cisterna magna using stereotactic technique under general anesthesia. The rats were then killed at specific time intervals between 4 hours to 7 days after SAH. Reverse-transcriptional polymerase chain reaction (RT-PCR) revealed the expression of iNOS mRNA in the homogenate obtained from the tissue around the circle of Willis one day after SAH (Day 1). No iNOS mRNA was detected either in the sham-operated animals, or at any of the other time intervals after SAH. An immunohistochemical study was performed to examine the localization of iNOS-positive cells in the central nervous system. Inducible NOS immunoreactivity was thus observed in the mononuclear cells and polymorphonuclear cells infiltrating into the subarachnoid space of the basal cistern on Day 1. This immunoreactivity persisted faintly on Day 2, but had completely disappeared on Day 7. A vascular diameter study disclosed a vasoconstrictive change in the middle cerebral artery after SAH. Taken together, these results are thus considered to confirm the expression of iNOS in the infiltrated inflammatory cells after the insult of SAH, which may therefore play an introductory role in the development of the pathological series of events after SAH, including vasospasm.