| INTRODUCTIONBody temperature is increased when the body is in hot environment. Recent studies demonstrate that the expression of heat shock protein 70(HSP70) is induced by exposure of cells and tissues to thermal conditions. HSP70 is a kind of non - specific cytoprotective protein, which has been shown to function as molecular chaperone, and can enhance cells to protect against heat - induced damage and repair heat - damaged and/or denatured proteins.Generally, body temperature doesnt go on increasing with the stimula of internal and external environment when it arrives at certain height,which is characterized as febrile ceiling. It indicates that there is a self - limitation structure for thermoregulation in the body, but the mechanism is still unclear. AVP is an endogenous antipyretic and the most sensitive active site is ventral septal area (VSA) in brain region. IL - 1β can elevate body temperature as endogenous pyrogen. It was reported that IL - 1β - induced fever response can be remarka-blely inhibited by the injection of AVP into VSA in rabbit. The present study aims to observe the effect of the expression of HSP70 in hypothalamus on IL - 1β - induced fever response and AVP content in hypothalamus and VSA after heat stress, so as to explore whether HSP70 takes part in the role of febrile ceiling.MATERIALS AND METHODS1. Animals and surgeryHealthy male Sprague - Dawley rats, weighing 200 - 250g, with basic body temperature(37. 5 ±1.0) ℃ were served for all the experiments. During theseexperiments,rats were individually housed in plastic cages at (22 ±2)℃. ambient temperature and (50 ± 2) % humidity and maintained on a 12:12 - h light -dark cycle with lights. Food and water were available ad libitum. Under intraperitoneal anesthesia ( ketamine hydrochloride and acepromazine maleate) , a 23 size of stainless steel cannula was implanted into the preoptic - anterior hypothalamus area using stereotaxic apparatus according to the brain atlas of rat, retained needle which was matched with it,and then anchored with dental acrylic. After operation, animals were returned to their home cages for recovery with free access to food and water for 7 days. Rats were habituates to experimental proce-dures by noninvasive handling daily for 7 consecutive days before the experiments. Digital thermometer probe was inserted 6 centimeters in ratsrectum when temperature was measured, and then the value was recorded after stabilization. Mean of three values 1 hour before administration was taken as baseline of pre -handling. After administration, rectal temperature was recorded respectively during experiments(to measure once every other 15 min in 0 - 1h, every other 30 min in 1 -2h, every other 60 min in 2 -8h). When the experiment was over, cannula's positions were checked to discard incorrect ones.2. Expression of HSP70 assay in hypothalamus tissue of rats Hypothalamus tissue was taken, homogenated and centrifuged. Then the su-pernatants were used to measure the expression of HSP70 by Western blotting.3. AVP levels assay in brainRats were put to death immediately at the peak of IL - 1 β - induced fever , and the brain were taken to boil 5 minutes in boiling physiological brine . Hypothalamus and VSA tissues 30mg were respectively weighted, homogenated , centrifuged and assayed concentration of AYP with radioimmunoassay.4. Statistical analysisResults were presented as mean ± SD . Change in body temperature were presented and analyzed with △T (℃) and thermo -response index . Data were analyzed using T - test.RESULTS1. HSP70 expression was induced increasingly after heat stress and reached peak at 12 hours;if rats were injected cycloheximide(CHX) before heat stress, HSP70 expression in hypothalamus was obviously inhibited at each time.2. Fever response was induced by the injection of IL - 1β into POA in rats, at the same time, AVP content in VSA was significantly increased.3. When rats were administrated IL -1β after heat stress, the extend of IL -1β - induced fever was obviously reduced, and AVP content in VSA wasn t significantly increased.4. When rats were injected CHX before heat stress,the extend of IL - 1β -induced fever wasnt obviously reduced,and AVP content in VSA was significantly increased.DISSCUSSIONThe experiment used IL-1β to make the febrile animal model of rat. Body temperature began to rise 15 minutes after administration in rats. This quick elevation of body temperature could have relation with direct administration into POA, and the peak of fever was at 2 hours after administration. AVP was an endogenous antipyretic, which was synthesized by hypothalamus, and conveyed to VSA through nerve fibres between hypothalamus and septal area to develop thermoregulation function. The experiment detected that AVP content in VSA was significantly higher in IL-1β and CHX + HS + IL - 1β groups than control group in the peak time of fever; However, AVP content in hypothalamus was slightly increased, but wasnt significantly higher than control group. This was consistent with previous report.It was reported that heat stress could induce HSP70 expression,which could enhance thermotolerance of cells. In this experiment, HSP70 expression was induced increasingly by heat stress, and then endogenous pyrogen IL-1β was administrated . It was obvious that the curve of body tempetature was low - flat,...
|
PDF Full Text Request