Effects Of Heat Stress On TNF-α-induced Fever And The Content Of CAMP In Rat Hypothalamus

INTRODUCTIONBody temperature of organisms can't exceed 41 ℃ in physiological or pathological condition. This phenomenon is called febrile ceiling. Present studies have demonstrated that there are endogenous antipyretic in organisms such as ar-ginine vasopressin ( AVP) andα - melanocyte stimulating hormone ( α - MSH). But biological mechanism of febrile ceiling is still unclear.Exposured to high temperature, cells, tissues or bodies can be induced to produce heat shock proteins (HSPs). This process is called heat shock reaction ( HSR). Several studies have demonstrated that HSP70 has an important role in cell protection, inflammatory reaction and immunization.This study observed the effects of HSP70 induced by heat stress on TNF -a - induced fever,and measured the change of cAMP level in hypothalamus, so as to explore whether HSP70 participates febrile ceiling and the possible mechanism.MATERIALS AND METHODS1. Animals and surgeryMale Sprague - Dawley rats, weighting 220 - 250g, purchased from China Medical University Animal Center, were housed individually. Room temperature was kept at (22 ± 2) ℃ Food and water were available ad libitum. Under intraperitoneal anesthesia (ketamine hydrochloride and xylazine) , a 23 bugle stainless steel was implanted into POA area by stereotaxic apparatus according to the rat brain atlas, and the cannula was anchored with dental acrylic. Rats were in-dividuaUy housed a week before experiments. Examine body temperature: digital thermometer probe was inserted 6 centimeters in rats'rectum. Value was recorded after stabilization. Mean of three values 1 hour before administration was taken as baseline of pre - handling. Record body temperature of rats after administration. When the experiment was over, cannula's positions were checked to discard incorrect ones.2. The expression of HSP70 in rat hypothalamus tissue assay Hypothalamus tissue was homogenated, centrifuged and the supernatantswere used to measure the expression of HSP70 by Western blotting assay3. cAMP level assayRat brain tissue was put into liquid nitrogen. 50 mg hypothalamus tissue was weighted, homogenate, centrifuged and assay concentration of cAMP with radioimmunoassay.4. Statistical analysisResults were presented as mean ± SD ( x ± s). Changes in body temperature were presented and analyzed with AT and thermo - response index. Data were analyzed using t - test.RESULTS1. The maximum expression of HSP70 in hypothalamus was attained at 12h after heat stress.2. In the febrile rats induced by TNF - α, cAMP level in hypothalamus was significantly higher.3. Injection of TNF - α 12h after heat stress could inhibit febrile effects, and the content of cAMP in hypothalamus was lower than TNF - a group.DISSCUSSIONIn this study, POA administration of TNF - α induced increase of body temperature, and at the same time cAMP level in hypothalamus was significantly higher than control group. This was consistent with previous report . That dem-...