title: Thermal adjustments to nonexertional heat stress in mature and senescent Fischer 344 rats.
abstract: The purpose of this study was to test the hypothesis that the rise in colonic temperature (Tc) during nonexertional heat stress is exaggerated in senescent (SEN, 24 mo, n = 12) vs. mature (MAT, 12 mo, n = 15) conscious unrestrained Fischer 344 rats. On 2 separate days (48 h apart) each SEN and MAT animal was exposed to an ambient temperature (Ta) of 42 degrees C (relative humidity 20%) until a Tc of 41 degrees C was attained and then cooled at a Ta of 26 degrees C until Tc returned to the initial control level. Control Tc was similar in the two groups for both trials. The rate of Tc change during heating was 63% greater (0.070 +/- 0.005 vs. 0.043 +/- 0.004 degrees C/min, P less than 0.05) and the time to 41 degrees C reduced by 36% (54 +/- 6 vs. 85 +/- 10 min, P less than 0.05) in MAT vs. SEN animals during the first exposure, although the cooling rate was slower in the MAT (0.048 +/- 0.004 degrees C/min) vs. SEN (0.062 +/- 0.006 degrees C/min) animals (P less than 0.05). The heating rate was unchanged in MAT animals between trials 1 and 2. However, SEN animals had a 95% increase in heating rate in trial 2 compared with trial 1 (P less than 0.05), and the corresponding time to 41 degrees C was decreased by 44% (P less than 0.05). As a result, rate of heating and time to 41 degrees C were similar in the two groups during trial 2. The cooling rate was similar between trials within each group.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Exercise and Sport Sciences, University of Arizona, Tucson 85721.
authors.forename: K C
authors.initials: KC
authors.lastname: Kregel
authors.forename: C M
authors.initials: CM
authors.lastname: Tipton
authors.forename: D R
authors.initials: DR
authors.lastname: Seals
mesh_terms: D000375:Aging / Q000502:physiology*; D000818:Animals; D001831:Body Temperature; D001833:Body Temperature Regulation / Q000502:physiology*; D005334:Fever / Q000503:physiopathology; D006358:Hot Temperature; D007700:Kinetics; D008297:Male; D051381:Rats; D011916:Rats, Inbred F344; D013312:Stress, Physiological / Q000503:physiopathology*; D015431:Weight Loss