Effects Of Exhaustive Exercise On Hypothalamic Monoamine Neurotransmitters And Related Parameters Of Rats In The Heat

Objective:To get a deep understanding of hyperthermia induced exercise fatigue(HIEF) through investigating exercise performance, thermoregulation and hypothalamic monoamine neurotransmitters changes of exercising rats in the heat.Methods:After six days adaptive treadmill training,24 male Sprague-Dawley rats were randomly assigned to 3 groups:Control group(C, N=8), Exercise group(E, N=8) and Heated exercise group(HE, N=8).Rats of E and HE group ran to exhaustion on a treadmill(28m/min) respectively in a temperate environment (23℃,-50%RH) and a high ambient temperature environment(33℃,-50%RH). Rats of E and HE group were killed immediately as soon as they ran to exhaustion and those of C group were killed without exercise and heat exposure. Rectal temperature(Tr) and time to exhaustion were recorded and samples were collected for measuring the levels of hypothalamic monoamine neurotransmitters, serum prolactin(PRL) and MDA, T-SOD, GSH, T-AOC in brain tissue.Results:High ambient temperature greatly decreased the time to exhaustion of rats in HE group (56.87±13.03min) compared to those in E group(152.13±11.84min, P<0.01), but significantly increased the Tr in HE group(40.40±0.35℃) compared to E group(39.70±0.21℃, P<0.01); The PRL level of HE group was greatly higher than that of E and C group (P<0.01), but there was no clear difference between the latter two groups (P>0.05); Compared to C group, levels of 5-HT,5-HIAA, DOPAC,5-HT/DA ratio in E group were greatly increased (P<0.01) and levels of NE and DA were greatly decreased(P<0.01); Levels of 5-HT and 5-HT/DA ratio were significantly increased in HE group compared to C group, but no significant difference was found between other parameters which changed similarly as those in E group. Further, levels of NE, DOPAC and 5-HIAA in group changed more significantly than those in HE group(P<0.05 or P<0.01). There was no significant difference among levels of T-SOD, GSH, T-AOC in all three groups (P>0.05), but levels of MDA in E and HE group were greatly increased compare to C group(P<0.05 or P<0.01), especially in HE group(P<0.01). Conclusions:During exercise in the heat, exercise performance of rats was greatly decreased and at the same time Tr was significantly increased which may mainly accelerate the onset of fatigue; Dynamic changes of Hypothalamic monoamine neurotransmitters and free radical metabolism may play important roles in exercise-induced fatigue in the heat, but the exact mechanism still needs further investigations.