Effect of Exogenous Melatonin on Plasma Corticosterone,Lucocorticoid Receptor mRNA and Change of Autoreceptors in Neonatal Rats with Hypoxic-Ischemic Brain Damage

Objective To observe the changes of plasma corticosterone(CS)and melatonin receptor 1(MR1)mRNA and glucocorticoid receptor(GR)in adrenal glands of neonatal rats with hypoxic-ischemic brain damage(HIBD)treated with exogenous melatonin.Methods Postnatal 7-day-old Sprague-Dawley rats were randomly divided into 4 groups:melatonin treated group,model group,sham operated group,normal control group.Rats in melatonin treated group were given exogenous melatonin 10 mg/kg by intra-peritoneal injection,while model and sham operated group with alcohol carrier(0.05 g/L)10 mg/kg,normal control group without intervention.Adrenal glands were obtained at different time points(2,4,8,12,24,48 h)after HIBD,semi-quantitative reverse transcriptase polymerase chain reaction(RT-PCR)analysis was used to measure the expression of MR1 and GR mRNA and Radioimmunoassay(RIA)for plasma corticosterone levels.Results The levels of MR1 and GR mRNA decreased at 2 h after HIBD,while plasma corticosterone raised significantly at the same time and peaked at HIBD 4 h in model group(Pa0.05),paralleling with the stress level.No obvious change of plasma corticosterone or MR1 was found after exogenous melatonin intervention in melatonin treated group(Pa0.05),and GR mRNA rebounded to the normal at HIBD 24 h.Conclusions GR in the glands may take part in the patho-physiological process of HIBD for the stress reaction.The exogenous melatonin may lower the endogenous corticosterone through the regulatory function of autorecepors,then up-regulate the GR mRNA,in order to lighten the excessive stress damage of HIBD.