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UDC 612.015.32:159.972-092.4
INFLUENCE OF EXPERIMENTAL CHRONIC STRESS ON THE STATE OF CARBOHYDRATE EXCHANGE IN RATS WITH DIFFERENT CHARACTERISTICS OF BEHAVIOR
1 P.K. Anokhin Research Institute of Normal Physiology, Moscow
2 A.I. Yevdokimov Moscow State University of Medicine and Dentistry, Moscow
3 I.M. Sechenov First Moscow State Medical University, Moscow
A.Yu. Abramova12, A.S. Pertsov3, E.V. Koplik1, S.S. Pertsov12
The research objective was to study the effect of chronic stress on blood glucose concentration in rats with various behavioral parameters in the open-field test. Daily 4-hour immobilization of animals in plastic tubes for 8 days served as a model of negative emotiogenic exposure. it was revealed, that the dynamics of glucose level during chronic stress depends on initial behavioral characteristics of the rats. Post-stress hyperglycemia in active animals was most pronounced after a single stress, in passive - by the 3rd day of repeated stress exposures. The specifics of abnormalities in carbohydrate metabolism during chronic stress in behaviorally passive and active specimens illustrates the importance of an individual approach to studying the systemic organization of physiological functions.
Keywords: chronic stress, rats, open-field behavior, carbohydrate metabolism.
Introduction
Sharp or protracted conflict situations caused by the inability to meet the leading biological and social needs of a person lead to the development of stress and related psychosomatic diseases [1, 2]. There is a convincing evidence pointing to the presence of significant individual differences in the resistance of mammals to the negative consequences of emotional loads [1, 3, 4, 5]. In experimental studies, it was established that the reliable criterion for the sensitivity of rats to stress are the features of their behavior in the "open field" test [6]. In particular, according to the survival rate under stressful effects, behaviorally active rats with high orienting and research activity are more stable than passive animals. An individual approach to studying the systemic mechanisms of the regulation of vital processes in mammals is of particular importance in terms of developing new methods of personalized medicine for the prevention and/or correction of post-stress dysfunction [7, 8].
Stress load in a person often leads to the development of metabolic disorders, in particular, to a violation of the metabolism of carbohydrates. A direct relationship between the effect of stress factors and the persistent increase in blood glucose levels with the subsequent formation of diabetes mellitus is shown [9, 10]. However, the specificity of changes in carbohydrate metabolism in individuals with different prognostic resistance to stress is not known. The nature of fluctuations in glucose levels in mammals in the dynamics of multiple stress loads has not been sufficiently studied.
Research objective
The aim of the work was to study the nature
of the effect of chronic stress on carbohydrate metabolism in behaviorally passive and active rats with different sensitivity to the development of negative effects of emotional loads.
Materials and methods
The experiments were performed in 76 Wistar male rats weighing 255.6 ± 2.8 g. The animals were kept in cages (4-5 individuals in each) at a temperature of 20-22 °C on a standard diet in artificial lighting conditions (9:00 -21:00 - light, 21:00-9:00 -darkness). All animals were pre-tested in an open field with the definition of behavioral indicators for 3 minutes [6]. To calculate the activity index of rats, the sum of the number of crossed peripheral and central sectors, peripheral and central racks, as well as the objects studied, was divided by the sum of the latent periods of the first movement and exit into the center of the open field. Depending on the initial behavior parameters in the "open field" test, the rats were divided into passive (n = 40) and active (n = 36), differing in the average activity index: 0.44 ± 0.02 and 2.73 ± 0.55 respectively.
The animals were immobilized daily in individual plastic containers for 4 hours at the same time of day (10:00-14:00). The glucose concentration in the blood of the rats was determined using a glucometer (Contour TS, Bayer) in the control, as well as on the 1st, 3rd and 8 th days of repeated immobilization stress. Previous studies have shown that changes in a number of physiological indices in animals on this model of stress load are expressed precisely in these time periods [11, 12]. In addition, it was found that the most significant violations of physiological functions are
observed at the end of the anxiety stage (39 hours after the emotional stress), and at the beginning of the stage of resistance (the 4th day) and 7 days after the exposure, compensatory processes appear in the body [13, 14].
To perform a comparative analysis of the results and to assess the reliability of intergroup differences, non-parametric tests were used - the Wilcoxon T-test and the Mann-Whitney U-test (Statistica StatSoft 6.1). Differences were considered statistically significant at a value of p <0.05.
Results and discussion
In the initial state, the blood glucose concentration of the behaviorally active rats was by 7.6% less than in passive animals (p <0.05, Table 1). The revealed differences in the basal level of glucose in the blood of rats with different parameters of behavior broaden the information about the characteristics of the parameters of carbohydrate metabolism. It was found, in particular, that the expression of glucose transporters mediating the transfer of glucose through the BBB to neurons and glial tissue depends on the sex and age of the animals [15].
Table 1
The concentration of glucose in the blood of rats under control conditions and at different time stages of chronic stress (mol /l, M±m)
Rats Control Repeated immobilization stress
1st day 3rd day 8th day
Passive 6,43±0,37 6,87±0,40 7,46±0,27 * 6,67±0,35
Active 5,94±0,17 + 7,14±0,22 * 6,49±0,32 + 6,14±0,37
Note. *p<0.05 compared with the control; +p <0.05 compared with passive rats.
Passive individuals were characterized by an increase in blood glucose after a single and especially triple immobilization stress (by 6.8 and 16.0% [p<0.05], respectively, compared with the control). By the 8th day of multiple stressful effects, the level of glucose in these animals decreased somewhat in comparison with that in previous periods, but exceeded the initial value.
The dynamics of glucose concentration in blood of behaviorally active rats subjected to repeated stress loads differed from that of passive individuals. The most pronounced increase in glucose content in active animals was observed after a single immobilization (by 20.2%, p <0.05 compared to the control, table). By the 3rd and 8 th day of daily stress, glucose levels in these rats progressively decreased compared to the 1st day of observations (by 9.1 and 14.0%, respectively), but remained above the initial value. It should be noted that on the 3rd day of the study, the analyzed parameter in active individuals was significantly less than in passive animals (by 13.0%, p <0.05).
It was found that multiple stressful effects on the model of daily 4-hour immobilization in rats are accompanied by the development of hy-perglycemia. This complements the results of our previous experiments demonstrating the nature of fluctuations in blood glucose levels in animals with different behavioral activity after acute stress loading caused by 1-hour immobilization [16].
At present, there is convincing evidence that stress effects of different duration and intensity have a specific effect on the metabolic rate. It was found that acute stress leads to an increase in blood glucose levels [17, 18]. Chronic stressful effects also cause changes in carbohydrate metabolism,
which is accompanied by a high risk of developing type 2 diabetes mellitus (metabolic syndrome) [19] with concomitant psychoneuroimmune disorders [20]. It is important that the severity of metabolic abnormalities under prolonged stress may differ depending on the strength and/or frequency of presentation of the stress factor [21]. Possible pathophysiological mechanisms underlying the metabolic stress effects include, in particular, changes in the activity of the renin-angiotensin system [22], disruption of the functions of the main enzymes of glucose metabolism and a decrease in the sensitivity of insulin receptors in the CNS [23], the involvement of neuropeptides (for example, hypothalamic orexin) [24].
In our studies, for the first time, specific features of the dynamics of carbohydrate metabolism in rats with different parameters of behavior in the "open field" test, with different prognostic resistance to negative consequences of stress, were revealed. Passive animals, predisposed to stress, show the most significant increase in blood glucose levels on the 3rd day of a daily 4-hour immobilization. Unlike these individuals, in active rats resistant to negative emotional stress, the degree of hyperglycemia was highest after a single stressful effect. Despite a slight decrease in the glucose content in the blood of rats with different behavioral characteristics by the 8th day of multiple stress loads (compared with that in previous periods), the studied index remained above the basal level.
The presented data broadens the modern understanding of the specificity of metabolic processes in mammals. Previously, there were described gender differences in the effects of stress, as a factor in the development of metabolic syndrome. For ex-
ample, it is shown that acute stress exerts a more pronounced effect on biochemical blood indices in male rats than in females [25]. A model of chronic psychosocial stress has been developed, in which "subordinates" are predisposed to metabolic disorders, while "dominant" animals are characterized by a normal metabolic phenotype [26].
Conclusion
Thus, there were revealed the characteristics of the parameters of carbohydrate metabolism in animals with different parameters of behavior in the open field, which have different sensitivity to the development of negative consequences of emotional effects. It was found that repeated stress loads on the model of daily 4-hour immobilization are accompanied by the development of hyperglycemia. The increase in the concentration of blood glucose in active animals is most pronounced after a single immobilization, and in passive - by the 3-rd day of repeated stress effects. The obtained data illustrate the importance of an individual approach to the study of the patho-physiological mechanisms of the development of stress-induced disorders.
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Contacts
Corresponding author: Pertsov Sergey Sergeyev-ich, Doctor of Medical Sciences, Corresponding Member of the Russian Academy of Sciences, Professor, Head of the Department of Normal Physiology and Medical Physics of the A.I. Yevdokimov Moscow State University of Medicine and Dentistry, Moscow.
125315, Moscow, ul. Baltiyskaya, 8. Tel.: (495) 6096700. E-mail: s.pertsov@mail.ru
Abramova Anastasia Yuryevna, Candidate of Medical Sciences, senior lecturer the Department of Normal Physiology and Medical Physics of the A.I. Yevdokimov Moscow State University of Medicine and Dentistry, Moscow. 127473, Moscow, ul. Delegatskaya, 20 (1). Tel.: (495) 6012245. E-mail: msmsu@msmsu.ru
Koplik Yelena Vladimirovna, leading research worker of P.K. Anokhin Research Institute of Normal Physiology, Moscow. 125315, Moscow, ul. Baltiyskaya, 8. Tel.: (495) 6012245. E-mail: nphys@nphys.ru
