Heat exposure induces tissue stress in heat-intolerant, but not heat-tolerant, mice

Figures & data

Table I.  Thermal responses of TOL, MT, and INT mice in two heat tests.

	TOL	MT	INT
Heat 1
Baseline (°C)	37.3 ± 0.2	36.4 ± 0.2^§	36.6 ± 0.3
Peak (°C)*	40.0 ± 0.2	40.8 ± 0.3^§	42.0 ± 0.2^§∥
Rate to peak (°C/min)^†	0.015 ± 0.01	0.024 ± 0.003^§	0.033 ± 0.001^§∥
Recovery time to 37°C (min)^‡	15.8 ± 1.0	18.0 ± 1.8	22.8 ± 2.2
Minimum during recovery (°C)^¶	34.0 ± 0.2	33.4 ± 0.3	31.8 ± 0.5^§∥
Heat 2
Baseline (°C)	35.9 ± 0.3	36.1 ± 0.4	35.6 ± 0.2
Peak (°C)*	40.4 ± 0.2	40.8 ± 0.3^§	41.9 ± 0.2^§∥
Rate to peak (°C/min)^†	0.025 ± 0.001	0.025 ± 0.003	0.041 ± 0.003^§∥
Recovery time to 37°C (min)^‡	16.0 ± 1.1	19.3 ± 1.7	23.8 ± 1.8^§
Minimum during recovery (°C)^¶	33.8 ± 0.2	33.4 ± 0.5	32.8 ± 0.3
Heat stress index, HSI	1.24 ± 0.10	2.01 ± 0.05^§	3.09 ± 0.14^§∥

Notes: P < 0.05, ^§compared to TOL; ^∥compared to MT. ^§ P < 0.05, compared to TOL; ^∥ P < 0.05, compared to MT

* Three consecutive minute averages of Tc before the end of heat exposure

^† Difference between baseline and peak Tc divided by time taken

^‡ Time from end of heat exposure to Tc first returning to 37°C

^¶ Three consecutive minute averages of lowest Tc during recovery following heat exposure.

Figure 1.  Representative tracings of SBP and DBP (top), HR (middle), and Tc (bottom) in a conscious INT mouse before, during, and after heat exposure. The signals were recorded simultaneously in real time from a single experiment. The ambient temperature (Ta) was obtained inside a mouse cage.

Figure 2.  Comparison of MAP and HR at baseline, during heat exposure, and recovery in TOL, MT, and INT mice. Peak and recovery values were obtained when Tc reached the highest and lowest levels during and after heat exposure, respectively. *P < 0.05, compared to TOL.

Table II.  Plasma cytokines, 8-isoprostane, corticosterone, and SOD in control, TOL, MT, and INT mice.

	Control	TOL	MT	INT
IL-6 (pg/ml)	9.5 ± 0.1	9.1 ± 0.2	9.2 ± 0.2	9.2 ± 0.3
IL-12 (pg/ml)	141 ± 16	101 ± 9	115 ± 16	109 ± 17
VEGF (pg/ml)	7.1 ± 1.0	6.7 ± 0.9	9.1 ± 1.3	6.3 ± 0.5
8-Isoprostane (ng/ml)	2.0 ± 0.2	2.1 ± 0.4	2.2 ± 0.8	2.8 ± 0.5
Corticosterone (ng/ml)	27.6 ± 3.0	36.3 ± 5.2	31.8 ± 10.7	51.9 ± 7.2*
SOD (units/ml)	23.7 ± 1.0	26.0 ± 0.9	31.4 ± 2.8	25.1 ± 1.5

*P < 0.05, compared to control.

Figure 3.  Tissue HSP72 levels in control mice and in TOL, MT, and INT mice following heat stress. One-way ANOVA revealed significant (F (3, 37) = 4.9, 16.3, 8.7, 11.6, and 27; P = 0.006, 0.0001, 0.0002, 0.0001, and 0.0001 for liver, kidney, heart, gastrocnemius muscle, and soleus muscle, respectively). P < 0.05: *compared to control; †compared to TOL; #compared to MT.

Figure 4.  HSP90, GR, and HSF1 protein levels in liver, heart, and gastrocnemius muscle tissues of control mice and TOL and INT mice following heat stress. *P < 0.05, compared to control and TOL.

Figure 5.  HSP72, HSP90, GR, and HSF1 mRNA levels in liver, heart, and gastrocnemius muscle tissues of control mice and TOL and INT mice following heat stress. *P < 0.05, compared to control and TOL.