СЕЗОННЫЕ ИЗМЕНЕНИЯ ГОРМОНАЛЬНЫХ ПОКАЗАТЕЛЕЙ ЩИТОВИДНОЙ ЖЕЛЕЗЫ У ДЕТЕЙ В УСЛОВИЯХ ВЫСОКИХ ШИРОТ

СЕЗОННЫЕ ИЗМЕНЕНИЯ ГОРМОНАЛЬНЫХ ПОКАЗАТЕЛЕЙ ЩИТОВИДНОЙ ЖЕЛЕЗЫ У ДЕТЕЙ В УСЛОВИЯХ ВЫСОКИХ ШИРОТ

Научная статья

Кубасов Р.В.^1, *, Кубасова Е.Д.², Калинин А.Г.³, Лупачев В.В.⁴, Мартынова Н.А.⁵

¹ ORCID: 0000-0003-1698-6479;

² ORCID: 0000-0001-9683-7814;

³ ORCID: 0000-0002-0425-6359;

⁴ ORCID: 0000-0002-8837-1177;

⁵ ORCID: 0000-0001-9581-379X;

^1-5 Северный государственный медицинский университет; Архангельск, Россия

* Корреспондирующий автор (romanas2001[at]gmail.com)

Аннотация

Регуляторные системы организма нуждаются в адаптивных изменениях к контрастным условиям при проживании на высокоширотных территориях. Целью нашего исследования явилось определение особенностей изменений гормональных показателей щитовидной железы в зависимости от сезонной продолжительности светового дня у детей мужского пола, проживающих в северных высокоширотных регионах России. Обследованы 242 мальчика в возрасте 10-16 лет, родившихся и постоянно проживающих на северных территориях Архангельской области. В сыворотке крови у них определены гормоны тиреоидной системы регуляции (тиреотропный гормон, тироксин и трийодтиронин) четырежды, в течение года, в зависимости от продолжительности светового дня. Определены сезонные особенности содержания гормонов. В период минимальной продолжительности светового дня (декабрь) концентрация тироксина была минимальной, а трийодтиронина - максимальной. В период максимальной продолжительности светового дня (июнь) определены максимальные концентрации тироксина и минимальные трийодтиронина. У обследованных мальчиков установлена факторная зависимость содержания в сыворотке крови уровней гормонов (тироксин, трийодтиронин,) от продолжительности светового дня, причем у детей во второй половине полового созревания эта зависимость более выраженная. Пик секреции тироксина у обследованных детей наблюдался в летний-осенний период, в пик трийодтиронина – зимний-весенний периоды. Продолжительность светового дня установлена, как один из факторов, влияющих на содержание сывороточных тиреоидных гормонов.

Ключевые слова: тиреоидное звено эндокринной регуляции, годовые ритмы, фотопериодичность, адаптация.

SEASONAL CHANGES OF THE THYROID HORMONAL LEVELS IN CHILDREN IN TERMS OF HIGHER LATITUDES

Research article

Kubasov R.V.^1, *, Kubasova E.D.², Kalinin A.G.³, Lupachev V.V.⁴, Martynova N.A.⁵

¹ ORCID: 0000-0003-1698-6479;

² ORCID: 0000-0001-9683-7814;

³ ORCID: 0000-0002-0425-6359;

⁴ ORCID: 0000-0002-8837-1177;

⁵ ORCID: 0000-0001-9581-379X;

^1-5 Northern State Medical University, Arkhangelsk, Russia

* Corresponding author (romanas2001[at]gmail.com)

Abstract

The regulatory systems of the organism need in adaptive changes to contrast conditions when living in the higher latitudes territories. The aim of our investigation was to determine the features of thyroid hormone level changes, depending on the seasonal daylight duration in male children living in the North region of Russia. 242 boys aged 10-16 years, born and permanently residing in the northern territories of the Arkhangelsk region, were examined. Hormones of the thyroid regulation system (thyroid-stimulating hormone, thyroxine and triiodothyronine) were detected in their blood serum four times during the year, depending on the daylight duration. Seasonal features of hormone content have been determined. During the period of minimum daylight hours (December), the concentration of thyroxine was minimal, and triiodothyronine was maximal. During the period of maximum daylight duration (June), the highest concentrations of thyroxine and lowest triiodothyronine were determined. The examined boys had a factor dependence of the serum levels of hormones (thyroxine, triiodothyronine) depending on the length of daylight, but in children in the second half of puberty, this dependence is more pronounced. The peak of thyroxine secretion was detected in summer-autumn, but the peak of triiodothyronine secretion was determined in winter-spring. The duration of daylight is established as one of the factors affecting the content of serum thyroid hormones.

Keywords: thyroid endocrine link, circannual rhythms, photoperiodic, adaptation.

Introduction

The study of changes in the functioning of the regulatory systems of the organism when adapting to natural factors is an urgent task in environmental physiology [1], [2], [3]. The need for an integrated approach when considering the adaptation of the body to the uncomfortable factors of the environment indicates the need for cooperation of research in various areas, the development of integrated parameters indicating the level of adaptation of the entire living system [4], [5] This task is much more complicated when it comes to the need to consider living systems in dynamics, the ratio of components in which varies according to the rhythm of the geophysical cycles of the environment. The rhythm of functioning is a fundamental property of a living organism, each physiological function of which is organized in time [6], [7]. Among the vast range of biological rhythms stand out circannual, infradian, circadian, which are rigidly synchronized with the periods of the geophysical environment [8], [9]. Daylight hours are one of the most stable values because they are the same at the same latitude during the same periods of the year. In high latitude areas photoperiodic dependence is one of the main rhythm-forming factors affecting the vital activity of the organism, including the human [10].

The endocrine system is the most important regulatory link that supports homeostasis [11]. When living in the Northern territories due to contrast changes in the duration of daylight there is an imbalance of endocrine functions [12].

The problem of studying the characteristics of endocrine processes, the dynamics of intra-and intersystem interactions becomes even more multifaceted when it comes to the growing body of children and adolescents. Conditions of the North impose additional requirements on the child's body, contributing to the development of disadaptation reactions [13]. The study of children and adolescents is relevant because it is at this age that the formation of the main regulatory systems takes place, which in the future will determine the nature of adaptation to uncomfortable living conditions [14].

Presented in the scientific literature information about the influence of photoperiods on the function of the pituitary – peripheral gland relates primarily to the adult population. Information about the formation of the hormonal profile in children and circannual dynamics are mostly represented by authors who have studied it in mid-latitude areas with mild, relatively benign climates depending on the season of the year [15], [16].

In connection with the above, the aim of our study was to determine the features of thyroid hormone level changes, depending on the seasonal daylight duration in male children living in the North region of Russia.

Materials and Methods

Within the year, four times (September, December, March, June) the same group of healthy boys and adolescents aged 10 to 16 years, born and permanently living in the Arkhangelsk region (Russian Federation) was examined. The study area is located at 61° north latitudes, and it refers to the transition zone between territories with uncomfortable (Arctic) living conditions and moderate latitudes. All children at the time of examination had no acute diseases and chronic somatic pathology. The total sample size was 562 persons. During the year, depending on the length of the light day, the following periods were considered in the territory where the studies were conducted: the period of the minimum duration of the light day (DLD) – 5 hours 35 minutes, December 21-22, the increase in the DLD – 13 hours 30 minutes, March 28-29, the maximal DLD – 19 hours 05 minutes, June 16-17, the decrease in the DLD – 12 hours 00 minutes, September 23-24.

Blood sampling from the ulnar vein at 8.30-9.00 a.m. on an empty stomach was performed in all examined patients. In blood serum, by radioimmunoassay analysis, determined the levels of pituitary thyroid stimulating hormone (TSH) and thyroid gland hormones: total thyroxine (T₄), total triiodothyronine (T₃) using commercial reagent kits “Immunotech” Czech Republic.

The variability in the distribution of different stages of sexual development within the same age was quite wide: in the same age periods, different children could be at least at two adjacent stages of puberty. Therefore, to assess seasonal changes in hormone levels, two groups were identified: the beginning of puberty (stage I and II of sexual development – 1 group) and puberty itself (stage III and IV of sexual development – 2 group).

Statistical processing of the obtained results, evaluation of the distribution of indicators, determination of the boundaries of the normal distribution was carried out. The critical significance level (p) was taken as 0.05 when testing statistical hypotheses. An average value, standard deviations were taken into account. To test the statistical hypothesis of the mean difference, we used ANOVA (Analysis of Variations).

Results The study revealed clear changes in the levels of hormones studied during the year (table. 1).  

Table 1 – Circannual changes of thyroid hormones in boys living in Archangelsk region Russia

Season (count of samples)	Means of hormones (1 and 2 groups of sexual development)
	TSH (unit/l)		T4 (nmol/l)		T3 (nmol/l)
December (n=69/67)	2,00±0,79	1,91±0,83	99,75±13,75	81,86±13,94	1,85±0,35	1,80±0,27
March (n=68/78)	2,01±0,69	2,25±0,89	96,51±14,59	87,99±13,89	1,93±0,34	1,94±0,33
June (n=66/71)	2,13±0,57	1,75±0,57	103,41±19,18	92,48±16,01	1,66±0,18	1,42±0,24
September (n=68/75)	1,97±0,68	1,81±0,79	101,97±17,95	86,70±11,27	1,68±0,39	1,84±0,32
Statistic differences of mean between groups (p)	All > 0,05	All > 0,05	Mar-Jun=0,023 Other > 0,05	Dec-Jun=0,03 Other > 0,05	Dec-Jun=0,006 Mar-Sep=0,014 Other > 0,05	Dec-Jun<0,001 Mar-Jun<0,001 Sep-Jun<0,001 Other > 0,05

In the pituitary-thyroid system, the most significant seasonal differences were found in the concentrations of thyroxine and triiodothyronine. In children, both at the beginning of puberty (group 1) and during the height of puberty (group 2), the maximum concentration of T₄ was determined in June and the minimum for group 1 – in March, for group 2 – in December. The highest average T₃ concentration for both the first and second group of children was determined in March. The minimum level of T₃ in group 1 children was determined in June and September and in group 2 children in June. Changes in the concentration of TSH during the year are less significant, and in children of group 1 the annual dynamics is more flattened than in boys of group 2, in which the highest values are determined in March.

According to the results of multiple regression analysis, it was found that with age, as puberty in boys, the factor of light day duration (Day-Light Duration – DLD) affects a thyroid hormone in the blood serum. Thus, in children in the early stages of puberty DLD has a significant effect on the concentration of T₃. In children of the older group, DLD has a significant effect on the concentration of TSH, T₄ and T₃.

Discussion

Among climatic and geographic conditions of the place of residence, affecting the thyroid endocrine link, for the Northern territories of one of the most significant factors can be considered as contrast photoperiodism. Especially demonstrative in this respect are the summer (June) and winter (December) periods, when there are maximum differences in the light regime. In addition, the length of daylight is a relatively constant, stable indicator, its influence is equally repeated every year at the same time [17], [18]. At the latitude where the studies were conducted (61°n) the difference in daylight hours between June (18 hours 40 minutes) and December (5 hours 35 minutes) was 13 hours 05 minutes, i.e. there is a significant difference in light conditions in the opposite periods of the year.

The study of endocrine parameters and interhormonal relationships during the year revealed the circannular dynamics, as well as to prove the presence of a significant impact of such a factor as the length of the day (Day Light Duration – DLD) and the degree of its influence on hormonal parameters.

In the examined children, an annual dynamic is observed for peripheral thyroid hormones, and in the older group of children the circannual differences are more clearly expressed. The highest concentrations of T₃ were determined in the period of minimum daylight hours (December) and increase in March, but minimal levels of T₃ was in the period of maximal daylight hours (June). The opposite dynamics of changes in concentrations was determined for thyroxine: i.e. the maximal levels of T₄ was detected during the longest daylight hours (June), and minimum – in December. Finally, annual changes in TSH are not so significant.

Thus, it was observed heterogeneity of changes in the levels of the studied hormones inside the pituitary – peripheral gland. A similar result was showed by other researchers [19], [20].

The role of the pituitary-thyroid system in the processes of adaptation of the body to changing environmental conditions is particularly evident in the winter. It is at this time to maintain homeostasis there is a need to increase the basic metabolism [21], [22], which is mainly carried out by means of triiodothyronine. And T₃ is formed mainly by peripheral conversion from T₄. Apparently, this explains the significant increase in winter – spring level of triiodothyronine, and a decrease in thyroxine is associated with increased conversion to T₃. In June, on the contrary, the peaks of thyroid hormone concentrations are changing opposite – determined by the minimum content of T₃ with a simultaneous maximum of T₄.

As you know, thyroid hormones are necessary to ensure the processes of growth and development of the body, differentiation of tissues, regulation of metabolism and energy, maintaining a certain level of activity of the functional systems of the body, the development of adaptive reactions [23], [24], [25]. TSH is the main, central regulating link of secretion of thyroid hormones, therefore, any changes in its concentration can lead to large-scale restructuring of the functioning of all systems of vital activity of the body, a disturbance of homeostasis [26], [27]. This may explain the lack of significant changes in TSH levels during the year.

Thus, the maintenance of homeostasis in winter is provided by the activation of the peripheral link of the pituitary – thyroid gland, through enhanced conversion of thyroxine into triiodothyronine.

Conclusions

• Boys of the higher latitude territory were found to have circannual changes in the blood serum of thyroid hormones (thyroxine, triiodothyronine).
• The peak of triiodothyronine secretion was determined in winter-spring; but the peak of thyroxine secretion was detected in summer-autumn.
• Factor dependence of the content of hormone levels on the duration of daylight hours was established, and in children in the second half of puberty this dependence is more significant.

Конфликт интересов Не указан.

Conflict of Interest None declared.

 

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