Effect of ThermalAcclimation on BloodPressure and Stress-induced Elevationof Core Temperaturein Spontaneously HypertensiveRats and Wistar Rats

Male adult rats of the three strains, spontaneouslyhypertensiverats (SHR), Wistar-Kyoto rats (WKY)and Wistarrats (WIS)were used. Rats of each strain, at 1 month old, were randomlydivided into three groups and chronicallyexposed to 3 different temperatures, 10℃, 30℃ and 22-24℃. Systolic blood pressure (BP) measured by the tail- cuff method and stress-inducedelevationof core temperature were compared.In cold-ac- climatedWKYand WIS, BP was significantlyhigher than that in the heat-acclimated rat. In SHR, geneticallyhypertensiverats, there was no significantdifferencein BP between cold- and heat-acclimated young adult rats, and BP in heat-acclimatedolderadult rats was higherthan that in cold-acclimated SHR. In normotensive rats, WKYand WIS, thermalac- climationaffectedsystemicBP. In normotensive strains, WKYandWIS, cold-acclimation in- creased BP, whereasheat-acclimation decreasedBP. Meanbody weightsin cold-acclimated rats were greater than those of heat-acclimatedones in all strains except for older adult WKY.For restraint stress, the consciousrat was pacedin a looselyfitting smallcage. Cold acclimated SHR (SHR-C) and WKY (WKY-C) were restrained at 10℃ and heat-acclimated SHR (SHR-H) and WKY (WKY-H) were restrained at 30℃. At the start of restraint, there was no significantdifferenceamongthe rectal temperaturesof these four groups. During the restraint stress, elevatedcore temperature was sustained and tail skin temperature decreased.Both values of rectal temperature(Tre) at the 30th min and increase of Tre (dTre) in the first 30th min during the restraint stress were in the order SHR-C>SHR- H>WKY-C>WKY-H. Valuesof Tre and dTre in cold-acclimated SHR were significantly greater than those in cold-acclimated WKY,and those valuesin heat-acclimated SHR were significantlygreater than those in heat-acclimatedWKY. Thermal acclimation,which started in one month old rats, scarcely affected developmentof hypertensionin SHR, whereasthermal acclimationproduceda significantdifferencebetween BPs in cold-and heat-acclimated normotensivestrains of rats. As for the influenceof thermalacclimationon the responsivenessof stress-inducedelavationof core temperatureto the restraint stress, the strain differencewas greater than the influenceof thermal acclimation.