| Background Neonatal hypoxic-ischemic brain damage(HIBD) is a serious disease caused by perinatal hypoxia.It not only threatens the lives of newborns ,and the survivors may also show disorders of psychomotor development,sleep-wake cycle reversion and endocrine disorders ,seriously impact on patient's quality of life. Circadian rhythms are known as the initiative adaptation of the organism to the periodic environment ,almost all physiological,biochemical and locomotor activities of organism are subjected to their regulation.Recent studies show that the occurrence and development process of many diseases are related to the abnormal circadian rhythm. There are two kinds of mammalian circadian clock: central circadian clock and peripheral circadian clock. The central circadian clock is located in the suprachiasmatic nucleus(SCN),which is formed by about 20000 neurons in the hypothalamus. Peripheral circadian clock is composed of non-SCN cells, including other regions of the central nervous system. The central circadian clock regulates the peripheral circadian clock by affecting the levels of neurohumoral factors(e.g.glucocorticoids, prostaglandins, epinephrine, melatonin, angiotensinⅡand retinoic acid).A large number of clinical investigations show that the functions of cardio-cerebral vascular system and the pathogenesis of cardio-cerebral vascular diseases have demonstrated the chronobiology rule, which is circadian rhythm. For normal people , whether adults or children , even newborns , the changes of their cardiovascular function , such as cardiac function , myocardial contractivity , cerebral blood flow velocity , blood pressure , heart rate , and electrocardiogram all have circadian rhythm. Currently, many changes of the clock genes have been investigated, so lead a new way to analyze and treat the disorders. Though obvious changes can be seen in HIBD neonatal cardiovascular functions, studies about changes of clock genes'expression on cardiomyocytes in HIBD neonatal are so few that mechanism of circadian disorders in HIBD is indefinite. At the molecular level,the intracellular circadian oscillator is a positive and negative transcriptional feedback loop, which is made up of various clock genes and its proteins, two most significant genes among which are Bmal1 and Clock.Objective To explore the effects of clock genes on circadian disorder in hypoxic-ischemic brain damage(HIBD) by comparing the level of BMAL1,CLOCK synthesis and the expression of Bmal1 mRNA,Clock mRNA on cardiomyocytes in HIBD group and control group neonatal rat.Methods 7-day-old Sprague-Dawley (SD) rats were randomly divided into 2 groups (36 pups each). HIBD models were set up according to modified Levine euthanized 0,2,12,24,36,48 hours afterwards. Semi-quantitative Reverse Transcriptase Polymerase Chain Reaction(RT-PCR)analysis was appllied to measure the expression profiles of Bmal1 mRNA and Clock mRNA ; Western Blotting for BMAL1,CLOCK protein on cardiomyocytes in rat,comparing the differences between two groups。Results Comparing with the control group:1,The levels of Bmal1 mRNA on cardiomyocytes in HIBD group increased at 48 hour(P<0.05),and there were no statistical significance at 0,2, 12,24 and 36 hours(P>0.05).2,The levels of Clock mRNA on cardiomyocytes in HIBD group increased at 36 hours,48 hours(P<0.05),and there were no statistical significance at 0,2, 12 and 24 hours (P>0.05).3,The levels of BMAL1 protein on cardiomyocytes in HIBD group decreased at 12 hours (P<0.05), increased at 48 hours (P<0.05),and there were no statistical significance at 0,2,24 and 36 hours(P>0.05).4,The levels of CLOCK protein on cardiomyocytes in HIBD group increased at 48 hours (P<0.05),and there are no statistical significance at 0,2,12,24 and 36 hours(P>0.05). Conclusion HIBD indeed affects the level of BMAL1,CLOCK protein and the expression of Bmal1 mRNA,Clock mRNA on cardiomyocytes in the neonatal rat, HIBD can interfere in transcription/translation of clock genes in cardiomyocytes.
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