State of endothelial function, lipid spectrum and features of coronary vessels structure of rats with obesity and insulin resistance under iodine deficiency conditions

The most pronounced changes in carbohydrate homeostasis were observed in animals of the groups 2^nd and 5 ^th (Table 2). Thus, in rats of the 2^nd group there was found an increase in blood serum insulin level at 20.85% (P < 0.001), glucose - at 43.06% (P < 0.01), HbAlc - at 91.92% (P < 0.001) and HOMA-IR index - at 94.02% (P < 0.001) relative to control values. In animals of the 5^th group there was an increase in the concentration of insulin - at 54.16% (P < 0.001), glucose - at 64.58% (P < 0.01), HbA1c - in 2.05 times (P < 0.001) and HOMA- IR index - in 2.54 times (P < 0.001) relative to data in intact animals. In obesity there was found an increase in the concentration of insulin - at 20.85% (P < 0.01), glucose - at 33.79% (P < 0.01), HbA1c - at 35.65% (P < 0.05) and HOMA-IR index - at 64.14% (P < 0.01) relative to control data. Carbohydrate metabolism in rats on an iodine deficiency diet did not differ significantly from the control group.

The experiment there was determined an absolute increase in BMI in animals of all groups at 30.43 - 71.74% (most significantly in rats of group 3^rd - at 52.17%, P < 0.01 and group 6^th - at 71.74%, P < 0.01).

In animals, under conditions of insulin resistance (2^nd group), there were observed an increase (in 2.41 times) in blood serum level of endothelin-1 (P < 0.01), TC - at 33.06% (P < 0.05), TG - in 2,04 times (P < 0.01) and LDL - at 53.85% (P < 0.05) against the background of a decrease in HDL - at 50.96% (P < 0.01) relative to the data in the control group (Table 3). Under such conditions, the AI increased in 5.32 times (P < 0.01) relative to the basic data. It is known that insulin resistance causes changes in the activity of lipoprotein lipase and hepatic triglyceride lipase and stimulates the synthesis of TG from fructose in the liver, which reduces the synthesis of phospholipids, causes the accumulation of LDL and deficiency of HDL [12].

Morphological examination of the vessels of the myocardium of insulin-resistant rats in part of the capillaries revealed endothelial cells with hypercellularity.

Table 3. The content of endothelin-1 and indicators of lipid metabolismin rats with insulin resistance, obesity, iodine deficiency and the conditions of their combination (M ± m; n = 15)

The nuclei of such endothelial cells are irregularly shaped, slightly hyperchromic, in places layered on top of each other. Freely located erythrocytes are noted perivascularly around a part of capillaries. In arterioles and minor arteries like capillaries, endothelial hypercellularity is noted. The wall of part of such vessels is unevenly homogeneous, ith areas of enlightenment (Fig. 1A). This causes unevenness of its thickness and inner and outer surfaces. Endothelial hypercellularity and uneven thickening of the vessel wall are accompanied by a narrowing of their lumen.

Fig. 1. Myocardial arteries of the rat with insulin resistance (A) and obesity (B); 1 - plasma permeation of the artery wall of the muscular type, 2 - deformation of endothelial cells, 3 - vacuoles in the cytoplasm of endothelial cells of small arteries of the muscular type, 4 - vacuoles in the cytoplasm of smooth myocytes of the middle lining of the arteries. Staining: hematoxylin and eosin, 40Qx

In obese rats, unidirectional but more significant changes in the studied parameters were observed. Thus, in the blood serum of animals of the 3^th experimental group there was found an increase in the content of endothelin-1 - in 2.31 times (P < 0.001), TC - at 51.62% (P < 0.01), TG - in 2.67 times (P < 0.001), LDL - at 76.92% (P < 0.001) and AI - in 9.38 times (P < 0.01) against the background of a decrease in the content of HDL at 64.42% (P < 0.001) (Table 3). In obesity, some lipoproteins accumulate in adipocytes, which inhibits the increased synthesis of cholesterol in the liver. At the same time, the activity of LDL receptors in adipose tissue increases, and the reverse transport of TC in HDL decreases. Being overweight is characterized by a decrease in tolerance to exogenous lipids. A long and high hyperlipidemic reaction to food intake in response to fat load has been established [13].

In overweight animals in the minor arteries of the myocardium, the focal clarifications of the cytoplasm of the inner membrane cells are singly visualized due to the presence of small transparent vacuoles. This is accompanied by a slight protrusion of the cytoplasm to the lumen of the capillary. The nuclei of such endothelial cells retain an elongated character. Small- vacuolar enlightenments in a middle cover in smooth myocytes are visualized in vessels (see Fig. 1B). There is a slight growth of connective tissue fibers around single minor arteries.

Restriction of iodine supply in animals has led to an increase of endothelin-1 in blood serum - at 80.17% (P < 0.01), TC - at 26.61% (P < 0.05), TG - at 65.38% (P < 0.01), LDL at 46.15% (P < 0.01), AI - in 3.30 times (P < 0.05) and to a decrease in HDL concentration at 34.61% (P < 0.05) (Table 3). It is known that iodine deficiency contributes to the development of hypercholesterinemia due to increased reabsorption of TC in the intestine with a decrease in the catabolism of LDL, which is due to a decrease in the content of LDL receptors in the liver and increase of its serum content. Prolonged iodine deficiency leads to a violation of the HDL structure, the change in the reverse transport of TC, which is the main antiatherogenic process [14].

In the arterioles of the myocardium of obese rats there is a weak condensation of chromatin in the nuclei of endothelial cells, in some - edema and vacuolation of the cytoplasm of endothelial cells, single macrophages and lymphocytes periarterially. Minor arteries with the phenomena of edema and vacuolation of the cytoplasm of endothelial cells, which slightly penetrates into the lumen of blood vessels. The nuclei are somewhat hyperchromic, irregularly rounded. Other endothelial cells that do not experience edematous phenomena have spindle-shaped extensions along the nucleus wall. The minor veins of the myocardium in the lumen contain a moderate number of compact erythrocytes. Endotheliocytes with clear spindle-shaped homogeneous nuclei extended along the vessel wall, a small amount of cytoplasm without signs of vacuolation, clasmatosis.

Attention is drawn to the changes in the studied parameters in insulin-resistant animals having been on the iodine deficiency diet (5^th group). In rats of this group, signs of endothelial dysfunction increased, reflecting a threetimes increase in endothelin-1 level (P < 0.001). Dyslipidemia, which we've observed in insulin resistance against the background of iodine deficiency, was characterized by an increased content of LDL (twice, P < 0.01), TC (at 50.00%, P < 0.01) and TG (in 2.33 times, (P < 0.01), AI - in 7.49 times (P < 0.05) relative to control data (see Table 3). Such changes of the lipid spectrum of blood can be caused by deficiency of hormones of a thyroid gland and insulin resistance which causes a decrease in the activity of lipoprotein lipase, which in turn increases the flow of free fatty acids into the blood from adipose tissue. The level of HDL, which has anti-atherogenic properties, in the blood serum of animals with combined pathology is reduced [12].

In animals of the group 5^th, the studied parameters differed significantly from the data under conditions of isolated iodine deficiency (endothelin-1 concentration increased at 67.38%, P_{4 5} < 0.05; AI increased in 2.91 times, P4-5 < 0 .05) and insulin resistance (the content of TC - at 12.73%, P_2-5 < 0.05; HDL - at 57.35%, P_2-5 < 0.01 have increased), which confirms the potentiation of the negative impact on the cardiovascular system of combined endocrinopathy.

Vessels of the microcirculatory bed of the animals' myocardium of the experimental 5^th group are filled with erythrocytes, dilated (Fig. 2A). In the lumen of individual vessels, red blood cells are compact, the boundaries between them are not clearly defined. Erythrocytes are also visualized perivascularly. In a small number of vessels of the microcirculatory bed, along with erythrocytes, there are single leukocytes. Endothelial cells are focal with slightly vacuolated cytoplasm, nuclei are of irregular ovoid shape, in places they are layered on top of each other. In a wall of single arterioles and minor arteries zones of the strengthened eosinophilic coloring are found, with homogenization of a wall in the given areas, hyalinosis of an arteriole of the myocardium is observed (Fig. 2B).

Under conditions of animals' being on high-fat and iodine-deficient diets at the same time (experimental 6^th group), the content of endothelin-1 in the blood serum has increased by 2.50 times (P < 0.001) compared to data of intact animals. Under such conditions, the indices of the lipid spectrum of the blood had the following dynamics relative to the control data: the concentration of total cholesterol has increased at 71.77% (P < 0.01), TG - by 3.11 times (P < 0.001), and LDL - by 2.85 times (P < 0.001), the HDL content has decreased at 70.19% (P < 0.001) (see Table 3). Such changes in the lipid spectrum of the blood caused an increase in AI - by 13.89 times (P < 0.001) relative to control.

Fig 2. The myocardium of rat with insulin resistance under iodine deficiency (1 - granularity of the cytoplasm of cardiomyocytes, 2 - karyopyknosis of cardiomyocyte nuclei, 3 - the plethora of the microcirculatory bed, 4 - circular equable accumulation of glycoproteins in the wall of arteriole, 5 - myocardial interstitial edema, 6 - the plethora of vessels of the microcirculatory bed vessels). Staining: hematoxylin and eosin (A), PAS (B), 40Qx

Significant differences between the studied parameters in animals of groups 6^th, 3^rd and 4th were established. In particular, in the blood serum of obese rats under conditions of iodine deficiency the concentration of LDL cholesterol was higher at 60.87% (P_3-6 < 0.01) compared to data in animals with isolated obesity. There was higher TG level - in 2.13 times (P_4-6 < 0.001), LDL cholesterol at 94.74% (P_4-6 < 0.001), but lower HDL cholesterol at 54.41% (P_4-6 < 0.01) regarding data in animals with mono iodine deficiency. At the same time, the AI in rats of the 6^th group was higher at 48.08% (P_3-6 < 0.05) relative to the data under the conditions of obesity and in 4.20 times (P4-6 < 0 .01) - under the conditions of iodine deficiency. The higher serum endothelin-1 content is noteworthy at 39.40% (P_4-5 < 0.05) compared to animals with isolated iodine deprivation.

In obese rats, against the background of limited iodine supply, the vessels of the microcirculatory bed are dilated and overflown with erythrocytes, which are sometimes compactly located next to each other. Endotheliocytes are with nuclei elongated along the wall, there is a swelling of the cytoplasm of endotheliocytes. In a wall of some minor arteries there are small, and also average-sized transparent vacuoles (Fig. 3A). The presence of vacuoles of medium caliber leads to the displacement of the nucleus to the periphery of the cytoplasm of individual smooth myocytes. Along with this, local enlightenments with blurred borders and irregular shapes are visualized in the wall, as well as areas of homogeneous eosinophilia, which are caused by excessive accumulation of glycoproteins in the vessel wall (Fig. 3B).

Fig. 3. The myocardium of rat with insulin resistance under iodine deficiency (1 - vacuolation of smooth myocytes of the wall of minor arteries of muscular type, 2 - local enlightenment in the middle lining of arteries, 3 - dilation of the interstitium perivascularly, 4 - dilation of the interstitium between the cardiac muscle cells; 5 - glycoproteins in the arteriole wall, 6 - edema of the myocardial interstitium). Staining: hematoxylin and eosin (A), PAS (B), 40Qx

As a result of the correlation analysis between the concentration of endothelin-1 in the blood serum and AI (r = 0.56, P < 0.05), TC (r = 0.63, P < 0.01), there was established a significant, direct correlation. There was also a direct, significant correlation between the content of total cholesterol and BMI in the blood serum (r = 0.52, P < 0.05). Such data confirm the role of endothelial dysfunction among the main pathogenetic mechanisms of cardiovascular disease and a significant risk factor for thromboembolic complications (heart attack, stroke, etc.).

In general, the tendency to increase the content of endothelin-1 in the blood serum and proatherogenic fractions of the lipid profile, AI, in experimental animals that were on high- fat and high-carbohydrate, iodine-deficient diets, draws attention. Due to the fact that endothelin-1 controls vascular tone, local processes of hemostasis, cell proliferation, such an imbalance can be a trigger mechanism for changes in lipid metabolism and a predictor of atherosclerosis, as well as one of the links in vascular complications in coronavirus disease. These biochemical disorders were consistent with structural changes in myocardial vessels. It can be argued that hypothyroid dysfunction, which can develop in residents of goiter-endemic regions, will adversely affect the development of endothelial dysfunction and dyslipidemia, and iodine deficiency is a factor that potentiates comorbid structural-metabolic changes in the cardiovascular system.

endothelin myocardial vessel iodine deficiency

Conclusions

The development of insulin resistance, obesity and iodine deficiency is accompanied by the development of endothelial dysfunction and dyslipidemia. Burdening by insulin resistance and iodine deficiency obesity is accompanied by an increase of endothelin-1 level in blood serum at 67.38% (only in the insulin resistance against the background of iodine deficiency relative to monoiodine deficiency), TC (at 12.73 - 49.19%), TG (at 52.83% - in 2.13 times), LDL (60.87% - 94.74%) and AI (at 48.08% in 4.20 times) in relation to isolated models of insulin resistance, iodine deficiency and obesity. BMI substantially affects the concentration of total cholesterol in the blood serum of experimental animals (r = 0.52). As a result of correlation analysis, a direct, medium-strength correlation was found between the concentration of endothelin-1 in the serum and AI (r = 0.56), TC (r = 0.63).

Such changes were consistent with structural violations. Morphological examination of myocardial vessels in experimental rats revealed structural changes in the microcirculatory bed (in arterioles and minor arteries, like in capillaries, endothelial hypercellularity is noted, which with uneven thickening of the vessel wall causes narrowing of their lumen). The most pronounced changes in the structural organization of blood vessels were observed in combined endocrinopathies, which significantly increases the cardiovascular risks in such conditions. In general, comorbid pathologies are manifested by the increased endothelial dysfunction and proatherogenic changes in the blood lipid spectrum, which is confirmed by changes in the structural organization of myocardial vessels.

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