STRUCTURAL CHANGES OF HEART IN EXPERIMENTAL ANIMALS IN MODELLING OF DIFFERENT VERSIONS OF ACUTE STRESS AND OPPORTUNITIES FOR MEDICAL CORRECTION

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1 UDC : STRUCTURAL CHANGES OF HEART IN EXPERIMENTAL ANIMALS IN MODELLING OF DIFFERENT VERSIONS OF ACUTE STRESS AND OPPORTUNITIES FOR MEDICAL CORRECTION V.R.Veber, P.M.Gubskaya, V.S.Bondarenko Yaroslav-the-Wise Novgorod State University, We studied the characteristics of cardiac remodeling in Wistar rats in the simulation of different variants of acute stress. The results showed an independent contribution of the parasympathetic nervous system in the development of structural changes in the myocardium. Changes of the extracellular matrix are more characteristic for the cholinergic stress, particularly an increase of extracellular spaces and to a greater extent in the right ventricle of the heart. Keywords: myocardium, Wistar rats,,, betaxolol, acute stress, left ventricle, right ventricle В работе изучена особенность ремоделирования сердца у крыс линии Вистар при моделировании различных вариантов острого стресса. Результаты исследования показали самостоятельный вклад парасимпатической нервной системы в развитие структурных изменений в миокарде. Для холинергического стресса в большей степени характерны изменения внеклеточного матрикса, особенно увеличение внеклеточных пространств, причем в большей степени в правом желудочке сердца. Ключевые слова: миокард, крысы линии Вистар, адреналин, прозерин, бетаксолол, острый стресс, левый желудочек, правый желудочек 39

2 At the heart of this work there are representations based on a large clinical experience, that during acute cardiac episodes the stress felt by patients may be revealed by different autonomic accompaniment: by predominance of adrenergic influences (classical view about endogenous and exogenous stress), significant activation of both sympathetic and parasympathetic parts of autonomic nervous system during stress and the third version is not ruled out, where cholinergic influences dominate during stress. However there are single studies on this subject in the literature [1-3]. We can assume that the different vegetative maintenance of stress leads to different variants of the structural remodeling of the heart and blood vessels. The study of these problems is extremely difficult in the clinic, so the myocardial remodeling during various vegetative variants of acute stress was investigated in the experiment. Objective. To study features of cardiac remodeling in Wistar rats in the modelling of different variants of acute stress and to examine the preventive role of selective beta-blocker betaxolol. Materials and methods The experiments were performed on male Wistar rats of similar age and weight, in accordance with the European Convention for the Protection of Animals used in the experiment (Directive 86/609/EES). Acute experiment was conducted on five series of rats, on 20 rats of similar age and weight in each series (Table 1). performed 2 hours after drug administration. The control series consisted of rats of the same age and weight which for 1 month were held in ordinary conditions without medication and exposure to stress. After material sampling the identification of left ventricular myocardial mass (MM) and right ventricular myocardial mass (MM) on the torsion scales, the calculation of myocardial mass index (weight of myocardium / weight of the rat, mg/g) of each ventricle were performed. Pieces of tissue were fixed in % neutral formalin, dehydrated at ascending alcohols and embedded in paraffincelloidin. Paraffin sections for morphological studies were stained with hematoxylin and eosin and Van Gieson. Using the grid of GG Avtandilov morphometry was carried out at 45 fields of vision in each ventricle at each experimental series. We estimated quantity (in volume percentage, % vol.) of cardiomyocytes, collagen, blood vessels and the volume of extracellular space, as well as the percentage of various structural elements to each other. Statistical analysis was performed using the program «Statistica 6,0». Results and discussion Different variants of the structural changes of the myocardium were obtained in experiment on Wistar rats during the modelling of three variants of stress with a predominance of adrenergic, cholinergic and mixed effects. For all three variants of stress (with a predominance of adrenergic, cholinergic and mixed effects) marked changes in myocardium of both ventricles were revealed [4-7]. Characteristics of the experimental unit Table 1 I model II model III model Adrenaline 50mkg/kg betaxolol 50 mkg/kg 0,4 mg/kg betaxolol 0,4 mg/kg Control group 50mkg/kg Three models of acute stress were created in the experiment: I model with a predominance of adrenergic influences (single intraperitoneal injection of adrenalin in a dose of 50mkg/kg); II model with a predominance of cholinergic effects of single intraperitoneal injection of the anticholinesterase drug in a dose of ) and III model with the simultaneous activation of adrenergic and cholinergic effects (a single intraperitoneal injection of both at a dose of 50mkg/kg and at a dose of). After 2, 6 and 24 hours and in 1 month after drug administration under ether anesthesia decollation and taking biopsy specimens for research were carried out. In the IV series of experiments simultaneously injected intraperitoneally a single dose of epinephrine and betaxolol (at doses of 50mkg/kg and 0.4 mg/kg, respectively), V series coadministration of and betaxolol (at doses of and 0.4 mg/kg, respectively). In series IV and V of the experiment decollation and biopsy specimens were It is known that myocardial remodeling begins with changes in the extracellular matrix. What happens in the simulation of different variants of stress? The results showed that in all of three models of stress the volume of the ECS changes significantly (Fig.1). In the most pronounced increase in ECS compared to control was noted in III model of stress after 6 hours (from 9,5 ± 0,8% vol. to 13,62 ± 1,26% vol., respectively, p < 0,05 ) and after 24 hours in II model of stress (up to 12,6 ± 0,67% vol., p < 0,05). In the the most significant changes in II model of stress (after a single injection of ) noted after 2 hours (6,58 ± 0,64% vol. in control up to 14,7 ± 0,80.%, p < 0,001), draws the attention an asynchronism of changes in and. Such significant differences under the influence of of changes of extracellular space in the right and the left ventricle tell us about expressed violations of liquid space, and, consequently, about violation of the 40

3 ,6,27 * 8,7 13,62 * 12,62 * 12,6 *,5 * 8, ,7 * 9,69 * 11,5 * 11,1 *,6 * 12,7 *,43 * ,6 5,5 * 2,8 * 4,35 * 3,9 * ,5 8,3 * 6,2 * 5,4 * 4,1 * 4,7 * 0 0 Fig.1. Change in volume of extracellular space (% vol.) in the myocardium of the leftand right ventricles under the influence of (I stress model), of (II model of stress) and the after simultaneous administration of and (III model of stress) liquid exchange and create a pronounced dissonance in the work of the heart as an integrated system. Particularly interesting that in 1 month after a single injection of drugs the full recovery of the extracellular matrix in the does not occur, in the the situation is similar, and only in 3-rd model the volume of ECS in 1 month comparable with the initial parameters of the control series (9,5 ± 0,8% vol. in control and 8,79 ± 0,79% vol. 1 month after drug administration, p > 0.05). Another component of the extracellular matrix is collagen (Fig.2). Compared with the control significant increase in the density of collagen (in 3 times) in the observed after 2 h in III model of stress (8,27 ± 0,67% vol. and 24,44 ± 1,35% vol., respectively, p < 0,05) and after 6 h in I stress model (24,3 ± 1,66% vol., p < 0,05), in the most significant swelling of collagen is observed in the I model of stress in 2hours after the injection of (25,8 ± 1,39% vol. compared to 5,07 ± 0,51% vol.in the control series, p < 0 05), and III models of stress (21,19 ± 0,96% vol. compared to5,07 ± 0,51% vol. in the control series, p < 0,05). With the achievement of the maximum increase in density of collagen after 24 hours after administration of (30,5 ± 1,98% vol., p < 0,05). On the basis of the results of our investigation, we can assume that and the parasympathetic nervous system along with sympathoadrenal promotes the earliest changes in the extracellular matrix. Furthermore it is known that the parasympathetic nervous system promotes production of collagen by fibroblasts [8], being a stimulator of fibrogenesis. Stimulating effect on fibroblasts, apparently, may be double, as part of sympathoadrenal level and from the parasympathetic level of autonomic nervous system, since in the course of the experiment most severe changes were revealed the in left ventricular myocardium in acute stress (after 24 hours) with the simultaneous injection of and, less pronounced - in a separate administration of and. In the the most pronounced changes in collagen were observed only with administration of. Even a single injection of and in doses that do not cause myocardial necrosis, led to myocardial remodeling, which lasted a day or even one month after a single injection of drugs. In the analysis of long-term effects (one month after a single injection of drugs) a marked increase in the density of collagen was noted in both ventricles in all of three models of stress, especially pronounced in III (simultaneous administration of and ) model of stress (from 5,07 ± 0,51 to.% in the control to 20,83 ± 1,30% vol. after a single injection of drugs in, p> 0,05, and 8,27 ± 0,67% vol. in the control to 24,09 ± 1,48 vol.% after a single injection of drugs in the, p > 0.05), which is a manifestation of fibrosis. In 2 hours after drug administration the most significant decrease in the density of the CMC (Fig.3) in the was noted in III model of stress (from 77,25 ± 1,43% vol. in the control series and up to 59,71 ± 2,29% vol. after 2 hours, p < 0,05) and in of II model of stress (from 78,56 ± 1,06% vol. in the control series to 59,6 ± 2,3% vol. after 2 h, p < 0 05). Authentic decrease in the density of CMC compared with control in persists and in a month after a single injection of drugs in all 3 models of stress, but is most pronounced in III model co-administration of, and. 41

4 ,5 * ,44 * 20,5 * 17,69 * 8,27 24,3 * 14,49 * 13,6 * 24,09 * 21,25 * 18,5 * 15,6 * 18,4 *, ,8 * 21,19 * 16,9 * 5,07 22,6 * 21,9 * 15,2 * 20,83 * 16,39 * 14,9 * 13,6 * 12,5 * 5 5 Fig.2. Change in the density of collagen (in % vol.) in the myocardium of the left and right ventricles under the influence of (I stress model), (II model of stress) and the simultaneous administration of and (III model of stress) 85 82, ,25 72,7 * 69,9 * 70,9 * 67,3 * 64,9 * 65,3 * 65,7 * 64,66 * 64,31 * 59,7 * ,56 74,8 * 66,2 * 64,47 * 60,8 * 62,19 * 59,6 * 74,8 * 72,6 * 69,7 * 69,21 * 65,21 * 57,4 * Fig.3. Change in the density of cardiomyocytes (in % vol.) in the myocardium of the left and right ventricles under the influence of and 42

5 The results showed that the independent contribution of the parasympathetic nervous system in the development of structural changes in the myocardium, no less than when the activation of the sympathoadrenal, and for the cholinergic stress changes in the extracellular matrix are more characteristic (significant increase in of ECS under the influence of, especially in the ). Since it is known that beta - blockers have protective effect when the action of mediators of the sympathetic nervous system on the myocardium is going on, it is certainly interesting if they have protective action in the predominance of cholinergic stress support? Experimental study has shown that betaxolol, despite the reduction of pathological effects on the myocardium of and, does not prevent the development of structural changes in the myocardium completely. Under the influence of simultaneous administration of betaxolol and in 2 hours the density of the CMC in the did not significantly change (77,25 ± 1,43% vol. in control and 77,54 ± 1,55% vol. after drug administration, p = 0.891). In the right ventricle compared with the control series with simultaneous administration of betaxolol and in 2 hours there was a significant decrease in the density of the CMC (from 78,56 ± 1,06% vol. up to 73,91 ± 1,62% vol., respectively, p = 0.018). Thus, the protective effect of betaxolol on the CMC of the right ventricle is less pronounced than in the left ventricle. The density of collagen in the compared with the control in 2 hours after the simultaneous administration of and betaxolol significantly increased (from 8,27 ± 0,67% vol. up to 11,92 ± 1,06 on.%, p = 0,001). Similar changes were noted in, but more significant swelling of collagen in the also draws attention compared with (5,07 ± 0,51% vol. in control and 16,59 ± 1,82% vol. with simultaneous injection of adrenalin and betaxolol, p = 0,001). The volume of of ECS in the compared with the control series in 2 hours after the injection of and betaxolol significantly decreased (from 9,5 ± 0,8% vol. tocontrol to 5,84 ± 0,86% vol. after drug administration, p = 0,002). In the there were no significant differences between the volume of ECS in the control series and in 2 hours after administration of and betaxolol (6,58 ± 0,64% vol. and 6,04 ± 0,70% vol., respectively, p = 0.571). The results show that with simultaneous injection of and betaxolol the increase in the density of CMC in the left ventricle from 77,25 ± 1,43% vol. in the control to 82,38 ± 1,82% vol. on drugs (p < 0,05 ) is noted. In the situation is analogous to changes in : with simultaneous injection of and betaxolol CMC density was significantly increased from 78,56 ± 1,06% vol. in the control to 83,12 ± 1,35% vol. on drugs (p < 0 05). With the simultaneous injection of and betaxolol density of collagen in the was comparable with the values of the control series as in the (8,12 ± 1,32% vol. and8,27 ± 0,67% vol., respectively, p = 0,911), so in the (4,54 ± 0,38% vol. and 5,07 ± 0,51% vol., respectively, p = 0.407). Reliable changes in the volume of ECS in the myocardium under the simultaneous injection of with betaxolol were not detected (9,5 ± 0,8% vol. in control and 7,99 ± 0,86% vol. with administration of drugs, p > 0,05), and in the in 2 h after simultaneous administration of and betaxolol swelling of the extracellular space was marked (the volume of ECS grew from 6,58 ± 0,64% vol. in the control to,98 ± 1,25% vol. with administration of drugs, p < 0,05). That is, betaxolol does not prevent the development of swelling in the myocardium of ECS of. It should be noted that in the right ventricle with simultaneous injection of and betaxolol, betaxolol and adrenalin structural changes of the myocardium in animals are expressed more significantly than in the left one. Conclusions 1. In experiments on Wistar rats during the modeling of three variants of stress with a predominance of adrenergic, cholinergic and mixed influences there are various versions of structural changes in the myocardium. For all three models of acute stress the most pronounced changes are observed in the myocardium of the right ventricle. 2. Betaxolol in the experimental study, despite the reduction of pathological effects on the myocardium by and, do not fully prevent the structural changes in the myocardium. 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