Effects of Hypothermia on Nitric Oxide Synthase Expression in Permanent Focal Cerebral Ischemia.

Kim, Kyu Hong; Kim, Hyung Dong

Original Article

Journal of Korean Neurosurgical Society 1998;27(9): 1175-1187.

Department of Neurosurgery, College of Medicine, Dong-A University, Pusan, Korea.

ABSTRACT

Hypothermia has beneficial effects on various pathophysiological state, and have been increasingly used in the treatment of giant basilar and other complex intracranial aneurysms. Systemic cooling decreases the cellular metabolic rate and excitatory neurotransmitter release. However, the mechanism by which hypothermia diminishes ischemic injury is not well understood yet. The effect and protective mechanism of hypothermia on neuronal injury following permanent middle cerebral artery occlusion in the rat were investigated by time-course evaluation of infarct area and the changes of nitric oxide synthase gene expression by RT-PCR. Permanent middle cerebral artery occlusion(PMCAO) was performed on 48 male Sprague-Dawley rats by extracranial insertion of a 3-0 nylon monofilament into the stem of middle cerebral artery via internal and external carotid artery. The rats were randomly assigned to a normothermic group(n=2), of which the body temperature were maintaned at 37degreesC till sacrificed, or to an hypothermic experimental group(n=12), in which moderate hypothermia(body temperature 27degreesC) was induced just before middle cerebral artery occlusion(MCAO) and kept for 2 hours after MCAO and then allowed to rewarm over 90 minutes. The experimental animals were killed at various time points after the onset of MCAO(2, 6, 12, and 24 hours; n= per time point). Infarct areas of rat brain slice were visualized by staining of coronal sections with 2, 3, 5-triphenyltetrazolium chloride and calculated infarct volume of normothermic animals were compared to consecutive hypothermic animals. Additional group of 2, 6, 12, 24 hour ischemic rats were sacrificed and cerebral cortex were separated. By reverse transcription of isolated mRNA of normothermic animals, cDNA were amplified by PCR, and the quantities of mRNA of NOS(eNOS, iNOS and nNOS) and beta-actin were compared to quantities of hypothermic animals by densitometry. In hypothermic group, a significant time-proportional reduction of the percent infarct of right hemisphere was recognized in the animals sacrificed at 2, 6, 12, 24 hour after MCA occlusion. RT-PCR products of NOS of hypothermic animals were significantly lower than that of normothermic animals. These findings indicate that, in the setting of permanent MCA occlusion, hypothermia markedly decreases ischemic neuronal injury, and one of the important mechanism of hypothermic neuronal protection is reduced induction of NOS gene(especially eNOS and iNOS gene).

Key Words: Cerebral ischemia; Hypothermia; Nitric oxide synthase; RT-PCR