The role of endotoxin,TNF-α,and IL-6 in inducing the state of growth hormone insensitivity

摘要

AIM: Critical illnesses such as sepsis, trauma, and burnscause a growth hormone insensitivity, which leads to anincreased negative nitrogen balance. Endotoxin isgenerously released into blood under these conditions andstimulates the production of proinflammatory cytokines suchas TNF-α, IL-6, and IL-1, which may play a very importantrole in inducing the growth hormone insensitivity. Theobjective of this current study was to investigate the roie ofendotoxin, TNF-α and IL-6 in inducing the growth hormoneinsensitivity at the receptor and post-receptor levels.METHODS: Spague-Dawley rats were injected withendotoxin, TNF-α, and IL-6, respectively and part of ratsinjected with endotoxin was treated with exogenoussomatotropin simultaneously. All rats were killed at differenttime points. The expression of IGF-I, GHR, SOCS-3 and β-actin mRNA in the liver was detected by RT-PCR and the GHlevels were measured by radioimmunoassay, the levels ofTNF-α and IL-6 were detected by ELISA.RESULTS: There was no significant difference in serous GHlevels between experimental group and control rats afterendotoxin injection, however, liver IGF-I mRNA expressionhad been obviously down-regulated in endotoxemic rats.Liver GHR mRNA expression also had a predominant down-regulation after endotoxin injection. The lowest regulation ofliver IGF-I mRNA expression occurred at 12 h after LPSinjection, being decreased by 53 % compared with controlrats. For GHR mRNA expression, the lowest expressionoccurred at 8 h and had a 81% decrease. Although SOCS-3mRNA was weakly expressed in control rats, it was stronglyup-regulated after LPS injection and had a 7. 84 timesincrease compared with control rats. Exogenous GH couldenhance IGF-I mRNA expression in control rats, but it didfail to prevent the decline in IGF-I mRNA expression inendotoxemic rats. Endotoxin stimulated the production ofTNF-α and IL-6, and the elevated IL-6 levels was shown apositive correlation with increased SOCS-3 mRNAexpression. The liver GHR mRNA expression was obviouslydownregulated after TNF-α iv injection and had a 40 %decrease at 8 h, but the liver SOCS-3 mRNA expression wasthe 4.94 times up-regulation occurred at 40 min after IL-6injection.CONCLUSION: The growth hormone insensitivity could beinduced by LPS injection, which was associated with down-regulated GHR mRNA expression at receptor level and withup-regulated SOCS-3 mRNA expression at post-receptorlevel. The in vivo biological activities of LPS were mediatedby TNF-α and IL-6 indirectly, and TNF-α and IL-6 may exerttheir effects on. the receptor and post-receptor levelsrespectively.