The Effects Of Heat Acclimation On Erythropoietin Of Liver And Kidney In Rats

Objective Heat acclimatization or heat acclimation (HA), is a series ofadaptive changes of the human body gradually produced by repeated effects ofheat to make the body adapt to hot environment and improve the ability of heattolerance. Large amounts of investigations have successfully adopted the way ofmanual intervention heat acclimatization as a countermeasure to improvehumans’ ability to adapt to hot environment, remaining the definite mechanismsunrevealed. The most commonly used measures are specific and non-specificphysical training, such as hypoxia exercise, physical strength and work loadexercise. Our study discusses the main effects of artificial heat acclimatizationon red blood cells and hemopoietin in rats and speculats the mechanismsunderling these effects.Methods Take the artificial heat acclimatization rats as the animal modeland observe the impact of heat acclimatization on red blood cells and hemopoietin in rats. Use the animal tempreture chamber to establish the ratmodel of artificial heat acclimatization and assign the animals to control, singleheat exposure and heat acclimatization group. Animals in control and single heatexposure groups were normally fed for10days in room tempreture. At the sametime, animals of heat acclimatization group were conducted heat acclimatizationfor10days. The body weight of animals in each group and the body weightchanges before and after heat acclimatization were monitored everyday. Thephysiological responses (pulse, respiratory rate and rectal tempreture) of animalsin single heat exposure and heat acclimatization group before and after thermalload were measured on the11thday. After recovery for24hours, the ventricleblood, kidneys and liver of the rats were taken, then automatic blood analyzerwas adopted to detect the the changes of hemoglobin, hematocrit value,erythrocyte mean corpuscular volume and RBC counts; ELISA was used todetect the hemopoietin (EPO) content of serum，kidney and liver; RT-PCR,Immunohistochemistry and Western blot were applied to test the mRNA andprotein expression of EPO in kidney and liver. Based on these works, thetime-coure of the alterations in the EPO content and expression were observedin heat acclimatization rats.Result After10days of heat acclimation, the heat resistance ability of ratsincreased obviously. The extents and rates of increasing heart rate, respiratoryrate and rectal temperature of HA group were significantly lower than that ofcontrol group. The parameters concluding hemoglobin, hematocrit value,erythrocyte mean corpuscular volume, RBC counts of rats exhibited almost nochange. The Erythropoietin content of kidney and liver increased markedly inHA rats; In single heat exposure rats, the EPO content also increased in kidneybut not in liver. The results of RT-PCR showed that, compared with control group, the mRNA expression of EPO in both kidney and liver were significantlyincreased in heat acclimatization (HA) group (p<0.05), when compared withcontrol group. The mRNA expression of EPO enhanced significantly by singleheat exposure in kidney but not in liver. The results of Western blot andImmunohistochemistry Assay showed that, compared with control group, theexpression of EPO of both liver and kidney was significantly increased in HArats, but in single heat exposure rats, the enhanced EPO expression onlyobserved in kidney.In time-coures study of alteration in EPO of HA rats，incerased EPOcontent in serum, liver and kidney firstly observed after first day of heatalcclimatizatoion, the expression of EPO preotein in kidney was enhanced byfirst heat exposure, but enhanced expression of EPO preotein in liver wasobserved in10days heat alcclimatizatoion rats.Conclusion Heat acclimation may significantly increase the tolerance tohigh temperature of rats. The relative red blood cell parameters are notsignificantly changed after heat acclimation. The mRNA expression and proteinexpression of EPO are significantly increased in both kidney and liver of ratsafter heat acclimation. At the same time, the EPO contents are apparentlyincreased in serum, kidney and liver. The data indicate that heat acclimationincrease the level of EPO in rats, and increased EPO may contribute to theincreased blood red cells in heat acclimation rats. In the early stage ofacclimatization, the increased EPO content may results from the enhaced EPOexpression in kidney.