| Background:Stress is the body's response, caused by all kinds of harmful or over-strong stimulates, such as environmental heat stress, or high temperature could result in different physiological , biochemical and histological changes in the body, Reinforcement lipid peroxidation ,and lead to atrophy of thymus gland and lymph, even metabolic dysfunction, and functional prostration in tissue and organs.Thymus gland is an important immune organ in the body, and the place where the T cells grow and maturate; it's the central part in the whole immune system. But various kinds of stresses, such as serious infection, injury, high temperature, lack of oxygen, radiation and oxygenized stress etc, can cause the damage to thymus gland, then leading to the atrophy and affecting the differentiation , growth of the thymus cells, causing the death of thymus cells.Through the development of immune nutrition, L-Arg is very noticeable with its unique physiological and pharmacological effect. With 2 bases, L-Arg is the strongest alkalescence amino acid in the semi-essential amino acid, it's indispensable only when the body is not mature or experiences severe stress, such as disease, hunger, infection, injury and over burdened with nitrogen, it helps the combination of protein, and adjust the immunity of the body. There are quite many reports on the protective effect of L-Arg on the heat stress injured the immune organ of body China and abroad, but the specific mechanisms still needs further research and discussion.Objective:Observe the physiological reflection of rats in heat stress, measure the thymus and spleen index and release of Cortisol in the hypothalamic-pituitary-adrenal axis, and survey cell membrane fluidity, and discuss the possible mechanisms of supplementing L-Arg could protect the damaged immune organ of rats after stress heat. Method:According to three factors model, randomly divide 144 male SD mice in puberty into 3 groups . Group A: Water supplementation Group B: L-Arg-supplemented (1.5g/kg.bw) Group C: VE-fed(300mg/kg). Put the 3 groups of mice into 41°C animal heat lab till 13th morning, ( dry ball 41 °C, wet ball 33.5 °C, relative humidity 60%), and heat stress the mice in different groups, 1 and 2h, then divide each group into normal temperature contrast group and 0, 4, 8h group after heat stress, 6 mice in each group. Measure and compare the physiological indexes of each group in different environments, such as weight, rectal temperature, thymus gland and spleen index; anesthetize the animals, get some blood from the abdomen artery, then measure the activity of SOD in blood serum with xanthine oxidase, the content of MDA in blood serum with Thio-malonylurea, and the consistency of serum cortisol with radioimmunoassay , as well as the macrophage membrane fluidity with confocal laser microscopy (fluorescence redistribution after photobleaching). Results:1. Physiological index changes: No distinct difference in the rectal temperature changes among groups (P>0.05), L-Arg supplemented group increases more weight than the water supplementation group (P<0.05), no distinct difference in the index of thymus gland and spleen (P>0.05); rectal temperature increases in all groups after heat stress (P<0.05), weight decrease is subject to the heat stress time (P<0.05), thymus gland and spleen index is greatly lower than normal temperature group (P<0.05); within same period heat stress, there is no distinct difference among the weight-decrease groups(P>0.05), thymus gland and spleen index of L-Arg supplemented group is higher than water supplementation group(P<0.05), whereas there is no noticeable difference between L-Arg supplement and VE-fed group(P>0.05); thymus gland and spleen index of water supplementation group after2h heat stress is significantly lower than lh(P0.05). After heat stress, all the thymus gland and spleen indexes at 3 time periods in each group are lower than normal temperature group (P<0.05), the two indexes reach the lowest point at 4h, and gradually rise up after 8h, but still lower than normal temperature contrast group (P<0.05).2. Changes of serum cortisol: No noticeable changes in the content of serum cortisol under normal temperature (P>0.05); the content of serum cortisol in each group after heat stress is significantly higher than normal temperature group (P<0.05), and reaches the highest at 4h, then gradually goes down after 8h, but still higher than normal temperature contrast group (P<0.05); the content of serum cortisol of L-Arg supplemented group is obviously lower than the VE fed and water supplementation group (P<0.05); the content of serum cortisol of VE fed and water supplementation group after 2h heat stress raises distinctly than lh(P<0.05), no distinct raise in L-Arg supplemented group(P>0.05).3. Changes of fluidity of macrophage membrane: No obvious difference in the changes of the fluidity of macrophage membrane in each group under normal temperature (P>0.05); no sharp increase of the fluidity of macrophage membrane in the water supplementation group after heat stress (P>0.05), the fluidity of L-Arg supplemented group and VE-fed group is significantly higher than water supplementation group (P<0.05), but no big difference between L-Arg supplemented and VE-fed group (P>0.05).4. Changes of SOD and MDA: No distinct changes in the content of the serum SOD and MDA in each group under normal temperature (P>0.05); the content of serum SOD and MDA in each group has an significant raise after heat stress (P<0.05), the serum SOD content of L-Arg supplemented group and VE-fed group is higher than water supplementation group (P<0.05), but MDA content is lower than water supplementation group (P<0.05), however, there is no significant difference in the serum SOD and MDA changes of L-Arg supplemented and VE-fed groups(P>0.05). Conclusion:1. Under normal temperature, there is no distinct change in weight, rectal temperature,thymus gland and spleen index of each group of mouse.2. Heat stress could cause acute atrophy in the thymus gland and spleen, supplementing proper amount of L-Arg has a preventively protective effect to the thymus gland, and lessens atrophy of thymus gland and spleen during heat stress.3. The protective mechanism of L-Arg works on thymus gland might be in these ways:(1) Control the cortical excreted from the hypothalamic-pituitary-adrenal axis, thus alleviate the repression on the immunity.(2) Improve the immunity of the heat stressed body by increasing the fluidity of macrophage membrane.4. Proper amount of L-Arg in advance could alleviate the damage and affect of heat stress, and in some way protect the body. |
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