Hormonal basis of seasonal metabolic changes in mammalian species.

Seasonal changes in external conditions (photoperiod, meteorological conditions, diet) cause adaptive changes in both energy and substrate metabolism in the animals of mammalian species. In summer, long days and a rich diet contribute to relative elevation in the levels of thyroid hormones (TH), but warmer weather lowers their levels. In winter, short days and a poor diet inhibit TH synthesis, but low temperatures increase their secretion. In addition, the results of our meta-analyses revealed a significant role of atmospheric pressure in circannual fluctuations of metabolic parameters in humans. The changes in photoperiod are generally viewed as a major factor contributing to seasonal rhythm regulation However, numerous data show that season-dependent metabolic changes in mammals could be also accounted for by meteorological factors and diet.

Dependence of Seasonal Dynamics in Healthy People's Circulating Lipids and Carbohydrates on Regional Climate: Meta-Analysis.

We analyzed the seasonal dynamics of lipid profile, glucose, and insulin in healthy subjects from 29 studies conducted in 23 regions, located in different climate zones ranging from subarctic to tropical. Our meta-analysis showed that people have higher the level of TC (total cholesterol), LDL (low-density lipoprotein), HDL (high-density lipoprotein), FBG (fasting blood glucose) in winter than in summer regardless of gender. Regional climate had a significant impact on the seasonal dynamics of lipid profile and glucose. TC, HDL, FBG seasonal fluctuations were more prominent in a climate that had a marked increase in average monthly atmospheric pressure in winter compared with summer as opposed to a climate where atmospheric pressure did not vary significantly in winter and summer. In a climate with humid winters, TC seasonal changes were significantly greater than in the regions with humid summers, most likely due to LDL seasonal changes, since HDL seasonal dynamics with peaks in winter were more prominent in the regions with humid summers. The level of triglycerides had prominent seasonal dynamics with peak values in winter only in the regions with a large difference in winter and summer air temperatures. The results of our current and prior meta-analysis allow for the conclusion that the seasonal dynamics of circulating lipids and glucose are frequently linked to the seasonal dynamics of thyroid-stimulating hormone and hematocrit. Dependence of the seasonal changes in the biochemical parameters on annual fluctuations in air temperature, atmospheric pressure and relative humidity is more obvious than on photoperiod changes. Supplementary Information: The online version contains supplementary material available at 10.1007/s12291-022-01064-6.

Dependence of seasonal dynamics of hemorrhagic and ischemic strokes on the climate of a region: A meta-analysis.

BACKGROUND: Cardiovascular events occur more often in winter than in summer; however, the dependence of strokes on various meteorological factors remains unclear. AIMS: The purpose of this meta-analysis was to determine the dependence of the circannual dynamics of hospitalizations for hemorrhagic stroke and ischemic stroke on seasonal fluctuations in meteorological factors. SUMMARY OF REVIEW AND CONCLUSIONS: For our meta-analysis, we selected 20 and 26 publications examining the seasonal dynamics of hemorrhagic stroke and ischemic stroke, respectively . The meta-analysis showed that hemorrhagic stroke is less likely to occur in summer than in other seasons and does not depend on a region's climate. The seasonal dynamics of ischemic stroke are not clearly expressed and are determined by the characteristics of a region's climate. In a climate without pronounced seasonal dynamics of atmospheric pressure and in wet winters, the vector of ischemic stroke incidents will not be expressed or slightly shifted toward winter. Low atmospheric pressure in summer is associated with an increased likelihood of ischemic stroke during this season compared to winter. There was also a relation between ischemic stroke risk with high relative humidity and a significant decrease in ρO2 in summer, but there is not enough evidence regarding this association. We did not reveal dependence of the seasonal dynamics of strokes on the amplitude of annual fluctuations in air temperature.

Seasonal variations in levels of human thyroid-stimulating hormone and thyroid hormones: a meta-analysis.

Seasonal dynamics in biological functions of mammals is regulated by melatonin-mediated circannual fluctuations in the secretion of thyroid-stimulating hormone (TSH) and thyroid hormones. Most anatomical and molecular structures responsive to photoperiod and melatonin secretion changes and the associated receptors are preserved in modern humans. This work aimed to determine the seasonal dynamics of TSH and thyroid hormone levels (total triiodothyronine (T3), free triiodothyronine (FT3), thyroxine (T4), free thyroxine (FT4) and to investigate the dependence of these variations on gender, age and amplitude of meteorological fluctuations. A meta-analysis of 13 panel and 7 cross-sectional studies was performed using Review Manager 5.3 (Cochrane Library). We found that circulating TSH levels were higher in winter than in other seasons, and FT4 levels were higher in autumn than in winter. T4 level had no pronounced seasonal dynamics. The level of circulating T3 was significantly higher in winter than in summer and FT3 levels were lower in summer than in autumn and spring. In addition, analysis of TSH seasonal dynamics (winter vs summer) accounting for gender differences showed pronounced increases in TSH levels during winter in women, but not in men; and also significant increases in FT4 levels during summer in men, but not in women. Seasonal dynamics of FT3 and T4 did not depend on gender. Seasonal dynamics of TSH did not change with respect to age. We also found that the extent of the seasonal dynamics of TSH is influenced by the extent of the annual dynamics of the partial density of oxygen in the air, as well as the magnitude of the annual dynamic of meteorological factors that determine it (atmospheric pressure and relative humidity).

[Changes in the autonomic control of the cardiovascular system in human aging. meta-analysis.]

It is known that with the aging, the adaptive capabilities of his body decrease. This is due to both changes in autonomic regulation and morphological remodeling of the cardiovascular system. To assess age-related changes in the autonomic nervous and cardiovascular systems, a meta-analysis was carried out, which examined changes in the aging of hemodynamic parameters [blood pressure (BP) and heart rate (HR)], heart rate variability (HRV), catecholamine concentrations, electrical activity of muscle sympathetic nerves (MSHA) , as well as the magnitude of the BR. The results of 32 works from the PubMed database were analyzed, in which healthy people of different age groups (27±5 and 64±5 years) were compared by the studied indicators. As a result of a meta-analysis, it was found that in older people compared with young people, the BP is higher, HR remains unchanged, but HRV and BR significantly decrease, the sympathetic-vagal balance shifts toward an increase in sympathetic effects on heart function, MSNA and plasma noradrenaline level increase. In the elderly people a loosening in autonomic control with an increase in sympathetic nervous activity causes an increase in the baseline of BP and its increase in conditions of stress. These changes are the cause of a decrease in the adaptive abilities of the old person and a substrate for the development of cardiovascular pathologies.

[Dose-dependent effects of melatonin on the functioning of the cardiovascular system and on the behavior of normotensive rats of different ages.]

The purpose of the work on normotensive rats of different age groups (3, 15 and 22 months) to study the synchronism between the functioning of the cardiovascular system and the locomotor activity of animals in the «open field¼ test by a single injection of exogenous melatonin in different doses (1 and 10 mg/kg). Studies have revealed the unidirectional dose-dependent effect of exogenous melatonin on the locomotor activity of rats of different ages and the age-dependent effect of melatonin on the parameters of the cardiovascular system. It shows the possibility desynchronization of the circadian rhythms of locomotor activity and the functioning of the cardiovascular system with aging, which can lead to a discrepancy between hemodynamic parameters and the level of locomotor activity.

[Effects of hyper- and hypothermia on hemodynamic parameters in people of different age groups. Meta-analysis.]

Age-related changes in thermoregulation occur due to the deterioration of the adaptive capacity of the cardiovascular system caused by remodeling of the vascular wall and myocardium, capillary density reduction, changes in the synthesis and clearance of neurotransmitters and vasoactive substances, as well as the inhibition of the vegetative mechanisms of hemodynamic parameters regulation. A common way to simulate hyper- and hypothermal conditions is to use a suit with tubes to fill with water at different temperatures. The purpose of this work is to conduct a meta-analysis of the hemodynamic parameters shifts when modeling hyper- and hypothermia using such a suit in people of different age groups. As a result of the meta-analysis, it was found that heating the whole body is accompanied by a decrease in blood pressure (BP) and an increase in heart rate (HR). The reaction of hemodynamic parameters to hyperthermia does not significantly change with aging. Cooling of the whole body is accompanied by an increase in BP without changing the HR. In hypothermia, the amplitude of the elevation of the systolic BP is greater in older people.

[ADRENERGIC AND IMIDAZOLINE MECHANISMS OF CIRCULATION CENTRAL REGULATION IN RATS OF DIFFERENT LINES].

The purpose of this work was a comparative analysis of the brain adrenergic and imidazoline receptors activation effects in laboratory rats with normal and elevated activity of the sympathetic nervous system. The experiments were carried out on male rats of Wistar and Wistar-Kyoto lines and spontaneously hypertensive (SHR) line. In freely moving rats the mean arterial pressure, heart beat-to-beat interval and cardiochronotropic component of baroreceptor reflex were recorded and analyzed at rest and emotional stress, caused by a conditioned signal. Agonist of imidazoline and adrenergic receptor clonidine, a primary agonist of imidazoline receptor moxonidine, selective alpha 2-adrenoreceptor blocker yohimbine and blocker of imidazoline and alpha - adrenergic receptor efaroksan were used for neurochemical analysis of adrenergic and imidazoline systems role in mechanisms of regulation of blood circulation. Our data have shown, that if adrenergic systems of the brain provide its participation in the long-term regulation of blood pressure, stimulation of imidazoline receptors activate the central link of baroreceptor reflex arc at the level of the medulla oblongata and also strengthening the processes of its suprabulbar modulation, caused by emotional stress.