The results of research conducted in the last decade testify to the leading role of the vascular endothelium in the regulation of the work of the cardiovascular system, the dynamics of the state of the vascular wall, and the regulation of vascular functions. The intima of vessels provides a dynamic balance between vasodilating and vasoconstrictive factors, regulates the growth and proliferation of subendothelial cells and non-cellular structures, affects vascular permeability [1]. Endothelial cell dysfunction is a characteristic feature of vascular disease and is characterized by a decrease in angiogenic potential and bioavailability of nitric oxide (NO), impaired vasodilation and increased inflammation [2]. The main role in vasodilation belongs to NO [3].
Research in recent years in the field of vascular physiology has shown that the NO molecule, which is synthesized by the vascular endothelium, has a wide range of bioregulatory effects. NO is an unstable short-lived molecule with a half-life of 2-30 seconds, followed by transformation into nitrite and nitrate and excretion in the urine. Both an excess and a deficiency of NO can be significant in the pathogenesis of many diseases, if we take into account its important role in the regulation of the activity of all cells, organs and systems and the vital activity of the organism as a whole in normal and pathological. Despite the enormous physiological importance of NO, the concentration dependence of its activity, basal concentrations, and how its levels fluctuate during certain pathological conditions [4], such as obesity and hypertension - the main components of metabolic syndrome remain unknown [5].
It is believed that vascular endothelium dysfunction plays a leading role in the formation and progression of hypertension. If in adults the issue of the regulatory influence of NO in hypertension is sufficiently studied, in pediatrics it remains open.

Abstract. Background. The issue of the pathogenetic influence of cortisol on the development of metabolic syn- drome (MS) in children is considered. The above-threshold values of cortisol are proposed to be taken as a marker of MS. The purpose was to study the relationship between blood cortisol and MS components in children. Materials and methods. We have examined 44 children with MS (study group; waist circumference > 90th percentile of the distribution according to age and sex) and 14 children without signs of MS (controls). The children of the study groups did not differ in age and gender. Anthropometric parameters (body weight, height, body mass index, neck, waist, and hip circumferences, waist/hip circumference index), blood cortisol and leptin, blood lipid and carbohydrate spectrum (total cholesterol, high- and low-density lipoprotein cholesterol, triglycerides, blood glucose, and insulin, HOMA-IR and glucose/insulin indices) were evaluated. The measurement of blood pressure with the calculation of the average level was conducted three times. The diagnosis of MS was formed according to the IDF guidelines, 2007. Results. It was found that the level of blood cortisol in children with MS (362.9 (255.5–634.1) μg/l) was 37.9 % lower than in controls (р > 0.05). The frequency of the above-threshold blood cortisol values in children of both groups was 31.8 and 50.0 %, respectively (р > 0.05). The study of dependence using the Spearman’s rank correlation coefficient between blood cortisol and anthropometric parameters (rmax = 0.16; p > 0.05), lipids (rmax = 0.4; р > 0.05), carbohydrate metabolism (rmax = 0.26; р > 0.05), and blood leptin (r = 0.19; р > 0.05) did not reveal any significance. A significant correlation was found between cortisol and systolic blood pressure. Conclusions. In chil- dren with MS, there was no significant difference in the level of blood cortisol compared to those without MS criteria. The association of blood cortisol and MS criteria other than systolic blood pressure has not been found. Although cortisol is important in the formation of systolic blood pressure, it cannot serve as a marker of MS in children since it is not a criterion-forming sign of MS.
Keywords: metabolic syndrome; cortisol; children