title: Cardiovascular-sympathetic 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 cardiovascular-sympathetic nervous system adjustments during nonexertional heat stress are exaggerated in senescent (S, 24 mo) vs. mature (M, 12 mo) conscious unrestrained Fischer 344 rats. During two separate trials (48 h apart), each animal was exposed to an ambient temperature (Ta) of 42 degrees C until a colonic temperature (Tco) of 41 degrees C was attained and then cooled at a Ta of 26 degrees C until Tco returned to the initial control level. Trial 1: heart rate (HR), mean arterial blood pressure (MAP), and arterial plasma concentrations of norepinephrine (NE), epinephrine (E), and lactate (La) were similar between the S and M groups during the baseline (control) period. The absolute increases in HR, MAP, NE, and E from the control period to the end of heating were of similar magnitudes between groups; however, La increased more in the S than M animals (P less than 0.05). During recovery, the declines toward control levels for all variables were similar or even more rapid in the S vs. M animals (P less than 0.05). Trial 2: the changes in HR and MAP during heating were similar to those observed in trial 1 in both groups. Generally, NE and E control levels were elevated in both groups compared with those in trial 1. The absolute increases in NE during heating were similar to trial 1 in both groups, whereas E increased to a greater extent than in trial 1 in the S animals (P less than 0.05).(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: D G
authors.initials: DG
authors.lastname: Johnson
authors.forename: C M
authors.initials: CM
authors.lastname: Tipton
authors.forename: D R
authors.initials: DR
authors.lastname: Seals
mesh_terms: D000064:Acclimatization; D000375:Aging; D000818:Animals; D001794:Blood Pressure; D001831:Body Temperature; D001833:Body Temperature Regulation; D002319:Cardiovascular System / Q000254:growth & development*; D004837:Epinephrine / Q000097:blood; D006339:Heart Rate; D006358:Hot Temperature; D007773:Lactates / Q000097:blood; D008297:Male; D009638:Norepinephrine / Q000097:blood; D051381:Rats; D011916:Rats, Inbred F344; D013312:Stress, Physiological / Q000503:physiopathology; D013564:Sympathetic Nervous System / Q000254:growth & development*
chemical_list: D007773:Lactates; D009638:Norepinephrine; D004837:Epinephrine