Neuroprotective Effects Of Exogenous Melatonin Against Hypoxic-ischemic Brain Damage Stress In Neonatal Rats

Objective To study exogenous melatonin(MT) against the stress response of hypoxic- ischemic brain damage(HIBD) in neonatal rats.Methods Postnatal 7-day-old Sprague-Dawley(SD) rats were randomly divided into four groups: sham operation group(group H), model group(group K), melatonin treated groups(group T) and physiological control group(group S). The adrenal gland were obtained in different times after HIBD, Radioimmunoassay(RIA) was used to measure adrenocorticotrophic(ACTH) and Cortisol levels in plasma, then the semi-quantitative Reverse Transcriptase Polymerase Chain Reaction(RT-PCR) analysis was used to measure the expression of melatonin receptor 1(MT1), Glucocorticoed receptor(GR) and corticotropin- releasing hormone receptor 1(CRHR1).Resultsâ‘ RIA shows that ACTH and Cortisol level shortly 2h after HIBD in the plasma had already began to rise, peak at 4h and then gradually declined by 48h. ACTH and Cortisol levels have remarkable differences before 24h within group T (P<0.05), there were significant differences at 2h, 4h, 18h, 24h and 48h between group K and T (P<0.05).â‘¡GR mRNA of group K levels significant declined within 2h after HIBD, then partially increased in 48h, but still lower than normal level(P<0.05). The expression of GR mRNA increased by 8h, and returned to their former levels at 24h in the group T.â‘¢The CRHR1 mRNA of group T and K were parallel at 2h after HIBD, but remarkably increased compareing with group S (P<0.05), then group T returned to the physiological level at 12h, but group K still at the peak by 48h.â‘£HIBD also made the MT mRNA expression in the lower level till 48h.