In the experimental groups of animals the effect of a long-term action of monosodium glutamate (MSG) on thymus gland, аs well as at the stages of its withdrawal was studied. The experimental animals were divided into six groups, depending on the term of decapitation. There was studied the effect on the body the 2-, 4-, 6-, 8-week administration of MSG in a dose of 30 mg/kg of rat body weight, which was dissolved in 0,5 mg of dechlorinated tap drinking water at room temperature. For a duration of 2, 4, 6 and 8 weeks the control rats were administered a placebo (0.5 mg of dechlorinated tap water at room temperature) while the diet remained standard.
The results of the conducted morphological study indicate that when MSG is administered to white male rats of reproductive age in a dose of 30 mg/kg of body weight, the structural reorganization of the thymus gland is identified. Already a 2-week feeding of the animals with MSG leads to thickening of the capsule of the thymus gland, which reaches its maximum size during the 6th week of the experiment (up to 98.16±1.35 µm – р<0.001) and even when 4 weeks passed after discontinuation of MSG, the thickness of the thymus capsule of the experimental animals decreases only to 80.96±1.21 µm – р<0.05. Thickening of the capsule occurs as a result of swelling and delamination of collagen fibers. The cortical septa are also thickened, but at the same time the differentiation of the organ into cortical and medullary substances is preserved. However, the electron microscope analysis test showed that the structure of thymocytes and epithelioreticulocytes of the experimental animals of E-II groups did not change during the 2nd week of the experiment. At this stage of the experiment (the 2nd week), the number of thymocytes increases in almost the same amount both in the cortical and medullary substances of the thymus lobules (by 11.7 % and 11.6 % respectively – р<0.05). However, from the 4th week of the experiment, a decrease in the number of thymocytes was identified, mainly in the medullary substance of the thymus lobules. The formation of irreversible changes when introducing MSG to the experimental animals is proved by a negative trend, namely, a decrease in the number of thymocytes in the medullary substance of the organ even 2-4 weeks after the withdrawal of the food additive (a decrease by 22.1 % and 26.5 %, respectively).
Already from the 2nd week of the experiment, changes in the vascular bed of the thymus are identified. Blood vessels inside the lobules of the organ, as well as in the surrounding connective tissue, are dilated and filled with blood. Already from the 2nd week of introducing MSG to the animals of the E-I group, a significant increase in the indicator of the outer diameter of the arteries wss identified (up to 53.04±1.05 μm in comparison with the animals of the control group К-І – р<0.05). The internal diameter of the arteries also increased and was significantly different from this indicator in the K-I group of rats (it was 26.87±1.12 μm – р<0.05). The area of the tunica media and the lumen of the arteries increases significantly, as well as the outer diameter of hemocapillaries in both the cortical and medullary substances of the thymus lobules of the animals involved in the experiment in the E-I group.
Already after 2 weeks of feeding the rats with MSG, their body weight increased by 5.4% (р<0.05) in comparison with the animals of the control K-I group. After the 8-week introduction of MSG, the body weight of the rats increases by 26.2% (p<0.001). After 2-4 weeks since the withdrawal of MSG, on the contrary, the weight of the experimental animals increased by 0.4% compared to the 8th week of the experiment (E-IV group), and by 26.6% compared to the indicator of the control K-V and K -VI groups (p<0.001). Therefore, in addition to the direct negative destructive effect of MSG on the structures of the thymus and its vascular bed, MSG-induced obesity and dyslipidemia also negatively affect the structures of the vascular components of the experimental animals’ thymus gland. However, the correlation between the change in the number of thymocytes in the cortical and medullary parts of the thymus and the increased body weight of the rats confirms the role of immune system disorders in causing an increase in body weight and obesity with long-term administration of MSG in a dose of 30 mg/kg of body weight of the experimental animals.
Key words: monosodium glutamate, white male rats, thymus gland, immune system, immunity, morphometry, inflammatory and degenerative changes, trophic status, body composition, weight gain, obesity, lipid metabolism, adipose tissue.
