Changes in the concentrations of brain natriuretic peptide (Nt-pro-BNP) in the blood in the regulation of hemodynamic reactions in practically healthy people living in the Arctic

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Introduction. Numerous studies have proven the relationship between the content of brain natriuretic peptide (BNP) in the blood and the problems of cardiovascular insufficiency [1-6]. Previously, we found that the concentrations of Nt-pro-BNP in the blood of practically healthy people are lower than in patients with coronary heart disease and hypertension, increase with age, in Arctic residents they are higher than in people living in the northern territories equated to the regions of the Far North [7]. Elevated concentrations of Nt-pro-BNP in the blood (more than 200 fmol/ml) were associated with increased concentrations of proinflammatory cytokines.
The aim of this study was to study the role of changes in the concentrations of Nt-pro-BNP in the blood in the regulation of hemodynamic reactions in practically adults living and working in the Arctic. To solve these issues, a comparative study of the concentrations of biologically active components of blood serum involved in the regulation of vascular tone was carried out in individuals with elevated and physiological concentrations of Nt-pro-BNP in the blood.
MATERIALS AND METHODS. 111 adults (46-55 years old) of practically healthy persons living and working on the Svalbard peninsula, as well as in the villages of Revda and Lovozero of the Murmansk region, including 66 women and 45 men, were examined. The comparison group included 118 healthy adults born and living in the Primorsky district of the Arkhangelsk region, 59 women and 59 men aged 46-55. The examination was carried out in June-July 2017-2021, in the morning hours (8.00-10.00) with the consent of volunteers and in accordance with the requirements of the Helsinki Declaration of the World Medical Association on Ethical Principles of Medical Research (2000), and also approved and approved by the Commission on Biomedical Ethics at the IFPA FGBUN FITSKIA UrO RAS (Protocol no.8 from 30.03.2022).
The content of BNP in the blood was determined by its N-terminal fragment (Nt-pro-BNP), which has a long half-life and is not exposed to endopeptidases [8]. The enzyme immunoassay method for determining the BNP content with Biomedica reagents (Austria) was used on an automatic enzyme immunoassay analyzer Evolis from Bio-RAD (Germany).
The complex of immunological examination included the study of hemograms in blood smears stained by the Romanovsky–Giemse method, the content of lymphocyte phenotypes in the blood (CD3+, CD4+, CD8+, CD10+, CD16+, CD19+, CD23+, CD25+, CD71+) in an indirect immunoperoxidase reaction using monoclonal antibodies ("Sorbent", Moscow) and by flow cytometry using the Epics XL apparatus of Beckman Coulter (USA) with Beckman Coulter Immunotech reagents (France).
Concentrations of endothelin-1, total NO, endogenous NO2, nitrate (NO3) (RnDSystems, USA), cortisol, norepinephrine, epinephrine (Bender Medsystems, USA) were studied in blood serum by enzyme immunoassay on an automatic enzyme immunoassay analyzer "Evolis" (Bio-RAD, Germany) with appropriate reagents. Austria).
The mathematical analysis of the results of the study was carried out using the application software package "Microsoft Excel 2010" and "Statistica 7.0" ("StatSoft", USA). The laws of distribution of values of immunological parameters were checked using the Pearson statistical criterion. Verification of the null hypothesis about the equality of all averages in the studied groups was carried out using a one-factor analysis of variance. Under conditions of non-compliance of the data with the law of normal distribution, the comparison of two different groups by quantitative characteristics was carried out using the nonparametric Mann-Whitney criterion. For each of these indicators, the parameters of descriptive statistics are calculated (M is the arithmetic mean, σ is the standard deviation, m is the standard error of the mean, Md is the median, R is the span, W is the coefficient of variation, the boundaries of the 95% confidence interval). The critical significance level (p) was considered 0.05.

Results.
Table 1 presents the average data of the parameters studied in the work in practically healthy adult women and men living in the Arctic and in the territory equated to the regions of the Far North.

Table 1. Levels of immunocompetent cells and cytokines in peripheral blood, depending on the concentration of Nt-pro-BNP in practically healthy individuals at the time of examination, M±m

 

Content	Women  (n=125)		Men (n=104)
	North  (n=59)	Arctic  (n=66)	North (n=59)	Arctic (n=45)
Nt-pro-BNP, fmol/ml	72,65±15,23	228,54±29,86***	76,57±18,33	198,42±22,71***
Leukocytes,109 cells/l	8,17±0,56	6,25±0,64**	8,11±0,81	6,24±0,72**
Neutrophils, 109 cells/l	5,06±0,41	3,43±0,43**	4,57±0,47	3,53±0,46**
Lymphocytes, 109 cells/l	2,66±0,19	2,14±0,17*	2,96±0,29	2,28±0,81*
Monocytes, 109 cells/l	0,35±0,05	0,63±0,04	0,55±0,15	0,65±0,14
Mature CD3+, 109 cells/l	0,63±0,04	0,51±0,05**	0,71±0,10	0,44±0,06***
CD25+, 109 cells/l	0,68±0,04	0,49±0,06**	0,62±0,06	0,41±0,05***
CD71+, 109 cells/l	0,45±0,03	0,32±0,04**	0,54±0,09	0,45±0,06*
HLADR II, 109 cells/l	0,75±0,06	0,64±0,05**	0,68±0,08	0,55±0,07**
CD10+, 109 cells/l	0,58±0,04	0,45±0,03***	0,41±0,06	0,38±0,04***
CD4+, 109 cells/l	0,56±0,04	0,44±0,03***	0,67±0,08	0,43±0,05***
CD8+, 109 cells/l	0,51±0,05	0,37±0,04***	0,63±0,07	0,42±0,06***
CD95+, 109 cells/l	0,42±0,13	0,41±0,14	0,56±0,10	0,39±0,07*
CD19+, 109 cells/l	0,54±0,05	0,48 ±0,04	0,68±0,08	0,51±0,07
CD23+, 109 cells/l	0,70±0,04	0,64 ±0,06	0,47±0,11	0,41±0,12
Endothelin-1, fmol/ml	0,75±0,08	1,91±0,11***	0,69±0,06	1,95±0,13***
NO,  mkmol/l	21,35±1,19	20,22±1,14*	28,32±1,21	26,24±1,17 *
NO2 , mkmol/l	17,65±1,33	16,23±1,67	15,63±1,42	13,28 ±1,36
NO3, mkmol/l	10,23±0,64	10,42±0,75	16,22±063	13,44±0,72*
Norepinephrine, ng/ml	223,68±22,34	419,52±65,34**	211,42±24,15	422,36±73,6**
Adrenaline, ng/ml	49,58±0,71	62,35±0,83**	51,34±0,85	56,41±0,95
Cortisol, ng/ml	223,68±22,34	429,52±65,34**	211,42±24,15	431,36±73,62**

Note: *p<0.05; **p<0.01; ***p<0.001 – the reliability of differences when compared with indicators for people living in the North

As can be seen from the data presented in Table 1, with an increase in the concentration of Nt-pro-BNP in the blood, the content of circulating leukocytes is lower, mainly due to neutrophil granulocytes of monocytes (p<0.01). It can be clearly assumed that this happens as a result of the redistribution of cells from the circulating pool to the marginal one.
Elevated concentrations of Nt-pro-BNP in the blood (more than 200 fmol/ml) were detected in 32.43% (36 people) among Arctic residents and in 27.11% (32 people) residents of territories equated to the regions of the Far North. On average, elevated propeptide concentrations were found in 32.80% among women (41 women) and in 25.96% (27 men). Comparative average data on serum concentrations of vasomotor substances in residents of the Arctic and territories equated to the regions of the Far North are presented in Table 2.

Table 2. Concentrations of biologically active vasomotor components and leukocytes depending on the concentration in the blood of Nt-pro-BNP, M±m

Studied parameters	Women (n=125)		Men ( n=104)
	<200 fmol/ml (n=84)	>200 fmol/ml (n=41)	<200 fmol/ml (n=77)	>200 fmol/ml (n=27)
Nt-pro-BNP, fmol/ml	78,79±20,47	333,81±80,09	70,12±15,26	262,97,93±73,52
Endothelin-1, fmol/ml	1,72±0,08	1,45±0,06**	1,74±0,15	1,05±0,09**
NO,  mkmol/l	23,42±1,28	20,56±136*	25,83±1,67	23,74±1,23*
NO2 , mkmol/l	19,61±1,36	15,69±1,58*	16,76±1,34	13,24 ±1,46*
NO3, mkmol/l	9,82±0,37	12,46±0,59	16,25±0,63**	14,31±0,55**
Norepinephrine, ng/ml	253,24±35,43	476,47±55,48**	225,72±42,28	457,56±48,62**
Adrenaline, ng/ml	64,28±6,57	51,35±7,45	69,34±5,85	52,41±0,95
Cortisol, ng/ml	245,42±42,54	468,66±55,83**	241,73±38,22	462,23±56,84**
Leukocytes,109 cells/l	8,46±0,62	5,78±0,76**	8,69±0,75	5,84±0,85**
Neutrophils, 109 cells/l	5,23±0,61	3,26±0,79**	5,28±0,68	3,25±0,82**
Lymphocytes, 109 cells/l	2,83±0,23	2,21±0,42	2,98±0,57	2,26±0,74
Monocytes, 109 cells/l	0,35±0,09	0,25±0,06	0,42±0,11	0,26±0,08
Mature CD3+, 109 cells/l	0,75±0,07	0,49±0,12**	0,71±0,13	0,55±0,08**
CD25+, 109 cells/l	0,77±0,09	0,45±0,11**	0,67±0,12	0,39±0,08***
CD71+, 109 cells/l	0,49±0,07	0,31±0,05**	0,51±0,08	0,41±0,12*
HLADR II, 109 cells/l	0,64±0,09	0,52±0,06**	0,71±0,12	0,56±0,11**
CD10+, 109 cells/l	0,61±0,05	0,43±0,07***	0,47±0,12	0,32±0,08***
CD4+, 109 cells/l	0,64±0,07	0,42±0,09***	0,68±0,09	0,41±0,07***
CD8+, 109 cells/l	0,58±0,08	0,35±0,09***	0,69±0,08	0,39±0,12***

Note: *p<0.05; **p<0.01; ***p<0.001 – the reliability of differences when compared with the indicators in individuals with a concentration of Nt-pro-BNP<200 fmol/ml in the blood.

At elevated concentrations of Nt-pro-BNP in the blood, the revealed activation of the redistribution of leukocytes from the circulating pool to the marginal one persists. On average, regardless of gender, individuals with elevated concentrations of Nt-pro-BNP (257.35±43.26 fmol/ml) have higher levels of norepinephrine (469.35±43.51 and 239.48±31.16 pg/ml; p<0.001) and cortisol (465.45±43.82 and 243.53±34.51 nmol/l; p<0.001). Elevated propeptide concentrations are distinguished by the absence of increased levels of endothelin-1 (1.25±0.06 and 1.73±0.09 fmol/ml; p<0.01) and adrenaline (51.88±5.21 and 66.81±6.53 pg/ml; p<0.05). The migration of neutrophil granulocytes from the circulating pool to the marginal one at elevated concentrations of Nt-pro-BNP persists; the migration activity of lymphocytes and monocytes is markedly reduced. So, an increase above the physiological limits of Nt-pro-BNP concentrations is associated with higher levels of norepinephrine and cortisol against the background of less pronounced endothelin-1 and adrenaline reactions, as well as the redistribution of lymphocytes and monocytes from the circulating pool to the marginal one.

Discussion.
A change in the ratio of circulating and wall pools is the main signal for the development of a hemodynamic reaction. Glucocorticoids ensure the preservation of the optimal level of circulating cells by increasing the content of neutrophils, erythrocytes and platelets by moving them from the marginal pool to the pool of circulating cells [9, 10]. Migration and perfusion of cells is ensured by slowing down the blood flow rate in the capillary network, which creates the possibility of cell adhesion to the capillary wall with its subsequent exit beyond the vascular bed [11, 12]. Neutrophil granulocytes are the first to appear in the focus of preventive reactions [13, 14]. The adhesive activity of lymphocytes at relatively high concentrations of Nt-pro-BNP in the blood is also noticeably higher, which is manifested by a decrease in their circulating concentrations, mainly mature and differentiated phenotypes. Serotonin, histamine, prostaglandins, kinins and acetylcholine released during adhesion and aggregation of blood cells [15], the content of which is noticeably higher in people living and working in the Arctic [16-18], ensure the migration of leukocytes through the vascular wall into tissues.

The endothelial mechanisms with the secretion of the vasoconstrictor endothelin-1 and nitrogen oxides are involved in the regulation of microcirculation most early [19]. The cycle of nitric oxide NO-NO2-NO3-NO, forms a wave of smooth muscle cell peristalsis, the phase of suction of the intercellular medium; in the absence of nitric oxide secretion, the endothelium constantly secretes endothelin vasoconstrictors. Increased shear stress and hypoxia stimulate the secretion of nitric oxide [20]. The release of vasodilators provides an increase in the lumen of blood vessels and locally increases volumetric blood flow with a slowdown in the rate of blood flow in the capillary network. When the blood flow slows down, the partial pressure of O2 decreases and pCO2 increases, there is a risk of hypoxia, respiratory and circulatory acidosis with a decrease in the pH of the cytosol, which leads to a violation of the function of the ATP-dependent proton pump responsible for maintaining the electrochemical gradient. The most frequent manifestations of insufficient regulation of the state of the microcirculatory bed is a deficiency of endothelium-dependent vasodilation as a result of a shift in the balance of synthesis of nitric oxide and vasoconstrictors towards the dominance of vasoconstrictors, primarily endothelin-1. Probably, the fact that endotheliocytes provide a cyclic effect of vasodilators and constant secretion of endothelin is important in this. Endothelin-1 has a powerful vasoconstrictive effect [21, 22]. The endothelium of the veins produces significantly more endothelins than the endothelium of the arteries [23]. With an increase in hydrodynamic pressure in the metabolic capillaries, the hydrophilic medium of blood plasma, overcoming the gradient of low albumin pressure, diffuses into the interstitial tissue and exits the vascular bed. Such situations may occur normally during pregnancy [24], they also develop with hypoxia, acidosis and dyslipoproteinemia. The increase in the permeability of the vascular wall begins during the first stage of short-term narrowing of microvessels and an increase in venous outflow with the participation of serotonin; in the phase of slowing blood flow, plasma exudation occurs through the walls of postcapillary venules. Plasma exudation is achieved by narrowing of postcapillary venules and expansion of terminal arterioles; under physiological conditions, much more fluid passes through the venular wall and the venular end of the capillary than through its arterial end. In all likelihood, an increase in Nt-pro-BNP concentrations causes the expansion of terminal arterioles, exhibiting vasadilation properties through stimulation of active energy-dependent transport of Na and K ions.

Endothelin-1, unlike other endothelins, can be synthesized not only by endotheliocytes, but also in vascular smooth muscle cells, neurons, astrocytes, hepatocytes, mesangiocytes, Sertoli cells, endotheliocytes of mammary glands, uterus, as well as tissue basophils [25]. The effects of endothelins are determined by the type of cellular receptor: receptors A and B2 mediate vasoconstriction by activating membrane phospholipase C; receptor B1, stimulates the synthesis and secretion of NO, natriuretic peptide and prostacyclin [24]. Increased concentrations of norepinephrine, increasing the heart rate and minute cardiac output, form the tension of the vascular network [26]. The secretion of catecholamines is induced by depletion of energy resources, disruption of the ATP-dependent proton pump and a decrease in intracellular Ph.
More than 90% of blood adrenaline is secreted in the chromaffin tissue of the adrenal medulla. Only cholinergic neurons, whose mediator is acetylcholine, participate in the innervation of the adrenal medulla. Acetylcholine performs the function of modulating synaptic transmission by changing the presynaptic level of Ca2+ and regulating the entry of calcium into the nerve terminal [27].
It is known that at least 90% of norepinephrine present in the blood is released from the presynaptic nerve endings by sympathetic nerves and only 7% of it is supplied to the circulation by the adrenal medulla. Norepinephrine, released during a nerve impulse from presynaptic nerve endings, acts on norepinephrine-sensitive adenylate cyclase of the cell membrane of the adrenoreceptor system, which leads to increased formation of intracellular 3-5-cyclic adenosine monophosphate signal conduction caused by the effector. Physiological stimuli of norepinephrine secretion are not only acetylcholine, but also serotonin, histamine, bradykinin, and angiotensin. The predominant increase in norepinephrine concentrations in the blood against the background of elevated levels of Nt-pro-BNP indicates that this reaction is provided by sympathetic influence.

Glucocorticoids provide the transition of urgent adaptive reactions carried out by catecholamines and prolong them. Under the influence of glucocorticoids, the number of receptors on the cell increases and their sensitivity to physiologically active substances, including catecholamines. The glomerular zone of the adrenal glands secretes aldosterone, which is regulated by the renin-angiotensin system, ACTH, dopamine, and depends on the potassium content. The bundle zone secretes mainly glucocorticoids. The mesh zone secretes glucocorticoids and androgens, is under the control of ACTH. As a rule, the activation of secretion to some extent concerns all three zones of the adrenal glands. Cortisol can bind to mineralocorticoid receptors, and significant concentrations of it can give mineralocorticoid effects. Due to the mineralocorticoid activity of cortisol, permease is synthesized in the epithelial cells of the distal tubules of the kidneys, which retains sodium and water in the body; in response to this, potassium excretion is increased a second time. Northerners have fairly high concentrations of aldosterone (up to 80.7ng% in men, up to 54.5ng% in women [28]. The main regulator of aldosterone secretion is the renin-angiotensin system with the production of angiotensin I and II, depending on the volume of circulating blood and sodium content. It is known that aldosterone ensures the preservation of sodium in the intercellular medium, which contains 7 water molecules in its hydrate shell, and BNP initiates the secretion of sodium against a density gradient. However, increased reabsorption of sodium and water in the renal tubules can lead to hypervolemia and hypertension, and increased excretion of potassium and hydrogen ions cause the risk of hypokalemia and metabolic alkalosis. An increase in pressure in the left atrium with hypervolemia and blood pressure increases the threshold of excitability of osmoreceptors and reduces the sensitivity of osmoregulation of the renin-angiotensin system, which in turn stimulates the secretion of antidiuretic hormone. The integration of the regulation mechanisms of these systems ensures the maintenance of plasma osmolarity in a very narrow range (285±5.0 mosm/kg).
Relatively high concentrations of glucocorticoids in the blood, a fairly significant proportion of people with elevated levels of cortisol, as well as the dependence of its content on a sharp change in photoperiodicity and seasonality in the north has been repeatedly confirmed and is a proven fact [29]. The cortisol content in the blood of those born in the north has a clear orientation to the upper limits: in 72% of the cortisol concentration above 400 nmmol/ l, the level of cortisol-resistant lymphocytes is also high (71.3± 2.8 vs. 59±78%), performing regulatory and effector functions, we have established the dependence of the level of cortisol-resistant lymphocytes on the concentration in blood cortisol [30]. Probably, one of the conditions for the survival of an organism under the stress of regulatory systems is the ability to develop an optimal adoptive response even at relatively high concentrations of glucocorticoids in the blood. Glucocorticoids not only mobilize plastic functions, creating a fund of free amino acids in favor of the formation of fats and carbohydrates, but also prevent the development of excessive tissue reactions.

So, an increase in sympathetic influence with an increase in the content of norepinephrine in the blood, an increase in blood pressure, shock and minute volumes of the heart, which occur at the same time, can lead to an increase in hydrodynamic pressure in various parts of the circulatory system. An increase in the hydrodynamic pressure above the membrane increases filtration and changes the volume of the intercellular medium pool. To prevent the loss of the intercellular pool, the effect of BNP is activated, initiating the secretion of sodium against the concentration gradient. The effect of natriuretic peptide is associated with simultaneous activation of norepinephrine and cortisol secretion. Unbalanced and prolonged activity of cortisol and norepinephrine secretion is a risk of disruption of the mechanisms for maintaining the osmolarity of the internal environment of the body in a very narrow range.
The main feature of the reactions of the cardiovascular system of a person living under the influence of polar climatic and geophysical factors is hyperfunction [31]. The implementation of thermoregulation is carried out by increasing the functions of external respiration and the cardiovascular system. Hyperfunction of external respiration causes an increased load on the small circulatory system by a spastic reaction of the pulmonary vessels to reduce heat transfer and increase the intensity of blood flow, to enhance water and gas exchange. The constrictor reaction of the surface vessels to prevent heat loss by convection and radiation may create a risk of increased peripheral resistance and hypertension in the large circulatory circle. Thus, conditions are created for increased load of the right heart and left ventricle. In Northerners, the density of the capillary network is increased to protect against tissue hypoxia and improve tissue supply [32].

Practically healthy individuals living in unfavorable climatic conditions for humans in the north have a lower life expectancy of erythrocytes, the average hemoglobin content in them with an increase in the concentration of fetal hemoglobin [33-35]. There is an increase in the microviscosity of the lipids of the erythrocyte membrane with an increase in cholesterol and monounsaturated fatty acids, which slows down the release of O2 from the erythrocyte, worsens the rheological properties of blood and reduces the rate of deoxygenation of intracellular hemoglobin [36]. The development of northern tissue hypoxia is characterized by changes at all stages of oxygen delivery, from external respiration to its consumption by tissues. In the Northerners, the reserve possibilities of regulating the permeability of capillaries for protein and fluid are reduced, and with age, the intake of protein and fluid from the blood into the tissues significantly prevails over the activity of excretion [37]. Changes in vascular permeability and erythrocytes can cause microcirculation disorders with increased aggregation activity of all blood cells, as well as create a risk of trophic capillary insufficiency and low tissue oxygenation efficiency [38]. Such changes in the microcirculatory bed lead to a redistribution of blood flows in microvessels dominated by the shunt component and to a significant decrease in nutritional perfusion. While energy consumption for life support in the North is significantly increased [39].

Conclusion.
People living in the Arctic and territories equated to the regions of the Far North have a higher content of natriuretic peptide precursor in venous peripheral blood. Elevated concentrations of Nt-pro-BNP in the blood of Arctic residents are associated with simultaneously higher levels of norepinephrine and cortisol against the background of less pronounced concentrations of adrenaline and endothelin-1, as well as the redistribution of lymphocytes and monocytes from the circulating pool to the marginal one. The established features of hemodynamic reaction regulation are more pronounced in adult Arctic residents and women.

 

 

About the authors

Liliya K. Dobrodeeva

N. Laverov Federal Center for Integrated Arctic Research

Email: dobrodeevalk@mail.ru
ORCID iD: 0000-0003-3211-7716
SPIN-code: 4518-6925
Scopus Author ID: 6603579532
ResearcherId: J-3753-2018

Dr. Sci. (Med.), professor, chief research associate

Russian Federation, Arkhangelsk

Samodova Samodova

N. Laverov Federal Center for Integrated Arctic Research of the Ural Branch of the Russian Academy of Sciences. Archangelsk, Russian Federation

Author for correspondence.
Email: annapoletaeva2008@yandex.ru
ORCID iD: 0000-0001-9835-8083

Candidate of Biological Sciences, a leading researcher, head of the laboratory of regulatory mechanisms of immunity Institute of Physiology of Natural Adaptations of the Federal State Budgetary Institution of Science of the Federal Center for Complex Studying the Arctic. Acad. N.P. Laverova Uro Ran.

Russian Federation

Svetlana N. Balashova

N. Laverov Federal Center for Integrated Arctic Research

Email: ifpa-svetlana@mail.ru
ORCID iD: 0000-0003-4828-6485
SPIN-code: 3475-3251
Scopus Author ID: 57191543951
ResearcherId: Q-4942-2017

Cand. Sci. (Med.), senior research associate

Russian Federation, Arkhangelsk

Ksenia O. Pashinskaya

N. Laverov Federal Center for Integrated Arctic Research

Email: nefksu@mail.ru
ORCID iD: 0000-0001-6774-4598
SPIN-code: 2201-0289
Scopus Author ID: 57261870200
ResearcherId: AAM-3348-2020

junior research associate

Russian Federation, Arkhangelsk

References

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