The Research Of Mechanism Of Water,Salt Metabolism Of Rat After Heat Stress And Heat Acclimatization

Objective:Through observations on the change of exercise ability, body temperature and the fluid-regulation hormones with the rats undergoing thermal environment, in addition to that, the synthesis of AVP in the hypothalamus and AVPV2R and AQP2in the kidney also being followed, we want to study intensively on the mechanism of water-electrolyte metabolism in the condition of heat stress and heat acclimatization.Methods:1) Heat stress group:Male Wistar rats were randomly divided into normal exposure group (N) without any treatment, prolonged exercise at normal room temperature group (E), exposure at high temperature for60min group (H) and prolonged exercise at high temperature group (HE). Record the exhaustive time of group E and HE, weight loss, plasma osmotic pressure, and the serum AVP, ALD, ANP, Na+, K+concentration are recorded. The expression of hypothalamus AVP mRNA, kidney AVPV2R mRNA and its protein expression, phosphorylation of AQP2expression of kidney by immune fluorescence detection, expression of AQP2mRNA and protein were also detected respectively.2) Heat acclimation group:Male Wistar rats were randomly divided into4groups. All the rats exercise to exhaustion at thermal temperature environment on the15th day after exposure14days without any treatment at normal room temperature in Group (A),14days of training at normal room temperature in group (B),14days exposure to60min per day at high temperature in group (C), and14days of training at high temperature in group (D). The indicators were the same as the heat stress groups.Results:1. Heat stress group:The time duration of group D was shorter than that of the general temperature exhaustive one, and the rectal temperature arising obviously at the extreme level both in the group of heat exposure and exhaustive. Because of the short time exercise, the high temperature exhaustive group loses weight not so apparently compared to the other two heat stress groups. At the same time, the plasma osmotic pressure and concentration of the blood serum AVP and ALD increase, and that is contrary to ANP. The increasing Na+, decreasing K+and the increasing of the ratio of Na+/K+are also observed. The expression of AVP mRNA in the hypothalamus and AVPV2R mRNA in the kidney are reinforced. What's more, we have found increasing immune fluorescent expression of the phosphorylated AQP2and expression of AQP2mRNA in the kidney.2. Heat acclimation group:This group shows longer time duration, more weight losing, great increase of plasma osmotic pressure and a extreme rectal temperature. After undergoing heat acclimatization, the rats' concentration level of serum AVP has fallen down with ALD increasing, while there is little difference of ANP. We can see that the AVP mRNA express lower in the hypothalamus and enhancement of the expression of AVPV2R mRNA and AQP2mRNA are obvious, both of whose protein expressions have been found increased.Conclusions:1. The exercise ability of rats has been impaired in the thermal environment, with the body weight losing seriously and temperature rising at extreme level.2. Hypothalamus AVP mRNA and phosphorylation AQP2expression in kidney of unacclimated rats increase after exercising in high temperature, then the short-term regulation of AQP2play a main role.3. AVPV2R and AQP2protein expression increase of heat acclimatization rat, the long-term regulation of AQP2improve the body's water retention capacity.4. Hypothalamic osmoreceptors "set point" change after heat acclimatization, the change of plasma osmolality is inconsistent with the hypothalamic secretion of AVP.