Features of the behavior of the rat with hereditarily determined arterial hypertension

The behaviour of spontaneously hypertensive rats (SHR strain), rats with inherited stress induced arterial hypertension (ISIAH, a new developed strain), and of their normotensive Wistar progenitors was studied. The open-field arena and a device for measuring the total activity in the home cage were used in the behavioural studies. The SHR were much more active in the open--field and home cage tests than the Wistar and ISIAH rats. The basal locomotor activity of the ISIAH strain was lower than that of the Wistar rats, but the ISIAH strain had an index of behavioural reactivity 2.7 fold higher than the Wistar or SHR strains. These behavioural characteristics corresponded to the hypertension patterns of the strains compared. Enhanced spontaneous locomotion of the SHR rats was associated with spontaneous increase in arterial blood pressure. The ISIAH rats showed low spontaneous locomotor activity, but high behavioural and blood pressure reactivity under conditions of mild emotional stress.     

Manifestation of oxidative stress in the pathogenesis of arterial hypertension in ISIAH rats.

The ISIAH rat strain with stress-sensitive arterial hypertension was intentionally selected to study the role of stress as a factor in the development of arterial hypertension. This study aimed to determine the role of reactive oxygen and nitrogen species (ROS and RNS) in the pathogenesis of hypertension in ISIAH rats. The nitric oxide concentrations measured by EPR were found to be significantly higher for hypertensive ISIAH rats compared with that for normotensive Wistar rats in both the aortic wall (2 times) and cerebellum (1.5 times). The activity of superoxide dismutase measured in the blood of ISIAH rats was found to be about 1.5 times lower compared with that of Wistar rats. These data support the suggestion that ROS and RNS, including superoxide radicals and nitric oxide, may play an important role in development of stress-induced hypertension in ISIAH rats. The tissue content of reduced thiols has been considered as a marker of oxidative damage. To study the tissue oxidative status we used an EPR method for quantitative determination of SH groups. The concentration of reduced thiols in the blood of ISIAH rats was much lower than that in Wistar rats (0.6 +/- 0.05 and 1.57 +/- 0.1 mM, respectively).     

Effect of chronic stress during prepubertal period of life on development of inherited arterial hypertension

The immediate and long-lasting effects of environmental stress during prepubertal life on arterial blood pressure (AP) were studied in rats with inherited stress-induced arterial hypertension (ISIAH) and normotensive Wistar rats. Two models of chronic stress (the 21st-32nd postnatal days) were used: repeated handling and unpredictable stress of daily exposures to a variety of mild physical or psychoemotional stressors. Chronic prepubertal stress did not affect the basal or stress-induced AP levels in young or adult Wistar rats. In ISIAH rats, chronic stress during the early phase of hypertension development did not accelerate its formation and did not augment its manifestation in adults. Moreover, the basal AP was decreased in young and adult ISIAH rats exposed to prepubertal stress as compared to the age-matched controls. AP elevation under acute stress conditions was lower in young ISIAH rats exposed to unpredictable stress. No long-lasting effect of prepubertal stress on acute stress-induced AP elevation in adults was found. The conclusion was drawn that moderate physical and psychoemotional training at prehypertensive stage can positively affect the development of inherited arterial hypertension.     

Genetic loci for spleen weight and blood pressure in ISIAH rats with inherited stress-induced arterial hypertension

Recently, the important role of the spleen’s function in hypertension development was demonstrated. In this study, the genetic control of absolute and relative spleen weight was investigated to reveal the genetic loci common for spleen traits and for arterial blood pressure at rest and under the emotional stress conditions in ISIAH rats with inherited stress-induced arterial hypertension. The search for genetic loci for absolute and relative spleen weight was performed on 6-month-old F₂ (ISIAH × WAG) hybrid males derived from a cross of hypertensive ISIAH and normotensive WAG rats. One significant QTL mapped on chromosome 1 and 5 suggestive loci were found for relative spleen weight. Four suggestive loci were detected for absolute spleen weight. All detected loci were novel. The significant QTL on chromosome 1 was common for relative spleen weight and arterial blood pressure at rest and under the emotional stress conditions in ISIAH rats. The results suggest that the manifestation of the stress-sensitive arterial hypertension in ISIAH rats may be related to the changes in genetic control of the spleen function.     

Disruption of latent inhibition in ISIAH rats with stress-sensitive arterial hypertension

Latent inhibition phenomenon is used in the study of processes of selective attention in the context reinforcing training. The purpose of this study was a comparative analysis of the ability to ignore irrelevant stimuli in hypertensive ISIAH rats and normotensive Wistar rats with different psychoemotional statuses. Latent inhibition was formed in the passive and active avoidance tasks the development of which was preceded by repeated presentation (pre-exposition) conditioned stimulus without reinforcement. In ISIAH rats, disruption of latent inhibition in both behavioural tasks was observed as compared with Wistar rats. These data suggest that the deficit of selection information in ISIAH rats is caused by congenital weakness of internal inhibition in the adaptation to anxiogenic stimuli.     

Expression of the renin angiotensin system genes in the kidney and heart of ISIAH hypertensive rats

The content of mRNA of renin-angiotensin system (RAS) genes was measured in the kidney and heart of hypertensive ISIAH and normotensive WAG rats using the real-time PCR. A statistically significant decrease in the mRNA level of RAS genes was registered in the kidney of ISIAH rats, including Ren (by 45%), Ace (43%), AT1A (34%), COX-2 (50%). The level of myocardial expression of AT1A decreased by 28% while Ace expression increased by 80%. These results suggest reduction of renal RAS basal activity in the hypertensive ISIAH rats, and therefore this strain of rats may be referred to the group of models of low-renin hypertension. The ISIAH rats were also characterized by a two-fold increase in the connective tissue sodium concentration and also by a small (but statistically significant) increase in plasma sodium concentration (139 ± 0.3 mmol/l versus 136 ± 0.25 mmol/l in WAG rats). These results together with a tendency to a decrease of plasma aldosterone level also support existence of a classical low-renin hypertension in the ISIAH rats. It is suggested that altered function of renal ion channels represents a basis for the development of low renin hypertension in the ISIAH rats. In addition, impairments in renal system of NO synthesis may also contribute to the pathogenesis of arterial hypertension in the ISIAH rats.     

A search for genetic loci responsible for emotional stress-induced arterial hypertension in the ISIAH rats

Hypertension is a widespread human disease caused by a complex interaction of a series of the genetic factors with both each other and the environmental conditions. In this study we aimed at determining the candidate genetic loci responsible for hypertension in the ISIAH rats and studying the dynamics of the relevant genetic and physiological mechanisms in rat ontogeny. The candidate genetic loci were identified from association of the microsatellite markers linked to these loci with arterial hypertension in rat F2 hybrids exposed to stress. Two populations of F2 hybrids of different age (3-4 and 6 months) were obtained by crossing hypertensive ISIAH and normotensive WAG rats. We present the results of cosegregation analysis for the following loci: the gene for the Na+, K(+)-ATPase alpha 1 subunit isoform (Atp1a1), the endothelin-2 gene (Edn2), the low affinity nerve growth factor receptor gene (Lngfr), and a region of chromosome 10 marked with the D10Rat58 microsatellile located 3 cM away of the aldolase C gene (AldC). The results obtained allowed us to localize the genes responsible for the stress-induced arterial hypertension in the ISIAH rats to the Atp1a1 locus (P < 0.05), chromosome 2 and to the Lngfr gene locus (P < 0.05), chromosome 10. The association of hypertensive status with the Lngfr gene was found only in young ISIAH rats whereas in adult rats of this line, hypertension was associated with the Atp1a1 locus.     

Chronic stress and forming of psychoemotional state during prepubertal period in rats

Immediate and long-lasting effects of chronic stress during prepubertal period (21-32 postnatal days) on anxiety- and depression-related behavior were studied in Wistar and ISIAH (inherited stress-induced arterial hypertension) rats. Significant interstrain differences were found. Both juvenile and adult ISIAH rats were less anxious in the elevated plus-maze and less depressed in the forced swimming test. Immediate effects of the prepubertal stress were similar in both rat strains and depended on the type of stimulation. Long-lasting effects were genotype-dependent. Chronic prepubertal handling exerted an anxiolytic effect in young ISIAH and Wistar rats and adult Wistar rats. Immediate anxiogenic effect of prepubertal unpredictable stress was preserved only in adult ISIAH rats. Depression-related behavior was intensified by the unpredictable stress in young animals, whereas the long-lasting effect was observed only in adult hypertensive rats.     

Function of hypothalamic-pituitary-adrenocortical system in hypertensive rats of ISIAH strain

Functional activity of hypothalamic-pituitary-adrenocortical axis has been studied under control and restraint stress conditions in rats with inherited stress-sensitive arterial hypertension (ISIAH strain) and in normotensive WAG (Wistar Albino Glaxo) strain. The levels of hypothalamic CRH-mRNA (in control and 2 hrs stress), pituitary and plasma ACTH and plasma corticosterone (in control and after 5, 15 or 30 min of restraint stress), were evaluated. Hypothalamic CRH-mRNA level was found to be approximately the same in the control rats of both strains. In control conditions, the pituitary and plasma ACTH content in ISIAH rats was significantly lower whereas the corticosterone level in the plasma differed from each other in both strain. The restraint stress resulted in a statistically significant increase of the CRH-mRNA in ISIAH rats and not in the WAG rats. Moreover, in spite of the lower ACTH level in stressed ISIAH rats, the corticosterone blood plasma concentration in hypetensive rats was significantly higher. The data obtained confirm the idea that the stress-dependent hypertension might be related to an enhanced sensitivity of the main endocrine links involved in the stress response organization.     

Analysis of polymorphic DNA markers cosegregation with arterial blood pressure in ISIAH hypertensive rats]

A search for DNA markers of hereditary arterial hypertension in ISIAH rats was performed by means of contemporary molecular genetic approaches. The backcross rat population used for the analyses was derived from a cross of the Wistar x ISIAH F1 progeny with the Wistar rats. Hybridization of the HaeIII-digested DNA samples with the (CAC)5 microsatellite probe revealed cosegregation of the basal arterial pressure value with the 4.8-kb polymorphic DNA fragment. Examination of the DNA polymorphism by means of polymerase chain reaction with arbitrary primers showed an association of the 700-bp polymorphic DNA fragment with the increase of arterial blood pressure under conditions of emotional stress.     

Activity of 11β-hydroxysteroid dehydrogenase of rat kidney and liver in inherited stress-induced arterial hypertension

11β-hydroxysteroid dehydrogenase (11β-HSD) catalyzing the interconversion of corticosterone and 11-dehydrocorticosterone is the key enzyme of glucocorticoid metabolism in rats. The activity of 11β-HSD in kidney of rats with inherited stress-induced arterial hypertension (ISIAH) was significantly (p < 0.05) higher than that in WAG rats. The opposite was observed in activity of liver 11β-HSD. No changes in the kidney 11β-HSD activity of both strains were observed under stress condition, however, the liver 11β-HSD activity in ISIAH rats was significantly (p < 0.05) higher as compared to basal level and stressed WAG rats. It is possible that the features of the 11β-HSD activity in ISIAH rats may reflect their hypertensive status.     

Renal and endocrine changes in rats with inherited stress-induced arterial hypertension (ISIAH)

Hypertensive inbred rats (ISIAH; inherited stress-induced arterial hypertension) present with baseline hypertension (>170 mmHg in adult rats), but attain substantially higher values upon mild emotional stress. We aimed to characterize key parameters related to hypertension in ISIAH. Kidneys, adrenals, and systemic endocrine parameters were studied in ISIAH of different ages and compared to normotensive Wistar albino Glaxo (WAG) rats. Native organs were obtained for Western and PCR analysis. Perfusion-fixed organs were prepared for histopathology and quantitative histochemistry. Plasma renin and adrenal hormones were measured. Renal morphology was unaltered in ISIAH. The hypothalamic-pituitary-adrenocortical (HPA) axis was constitutively upregulated with enlarged adrenal cortices and enhanced plasma corticosterone levels. Plasma renin activity was not different between groups, whereas aldosterone levels were in part reduced. Juxtaglomerular NO synthase type 1, cyclooxygenase type 2, and renin expression were significantly reduced, whereas tubular gene products related to sodium transport (bumetanide-sensitive Na, K, 2Cl cotransporter type 2; thiazide-sensitive Na, Cl cotransporter; epithelial Na channel-α; 11β-hydroxysteroid dehydrogenase type 2) were increased. These data suggest enhanced volume conservation by the kidney. Our data define ISIAH as an attractive model for the renal components determining salt and water homeostasis in hypertension. The specific condition of a basally stimulated HPA axis is highlighted, including the option to study effects superimposed by emotional stress.     

Genetic correlation between the arterial pressure response during emotional stress and the alpha1-adrenoreceptor concentration in brain regions]

Arterial blood pressure reactivity to the emotional stress and brain alpha 1-adrenoreceptors concentrations were studied in hypertensive (ISIAH strain) and normotensive (Wistar strain) rats and their F1 and F2 hybrids. Significant correlations between the stress-induced increase in the arterial blood pressure and the amount of alpha 1-adrenoreceptors in hypothalamus (+0.46) and medulla (+0.38) were found in the F2. This cosegregation may point to the significant role of genetically determined peculiarities of expression of alpha 1-adrenoreceptors in brain regions during pathogenesis of arterial hypertension in the ISIAH strain.     

Expression of the pro-opiomelanocortin gene in rats with inherited arterial hypertension]

Expression of pro-opiomelanocortin (POMC) gene in pituitary of rats from newly developed hypertensive strain (ISIAH strain) was studied by dot hybridization. The pUC8 plasmid containing 900 base pair (bp) segment or the human POMC gene corresponding to the major portion of the 3'-nontranslated mRNA region and 60 bp coding for the signal peptide, was used as a probe for hybridization. It was found that the expression of the POMC in pituitary of the hypertensive JSJAH rats was more than 3-fold gene lower as compared to normotensive Wistar strain. The latter is the original strain from which the ISIAH rats were bred. The mechanism of this phenomenon and its possible relation to the arterial hypertension are discussed.     

Effect of chronic stress in prepubertal period on sexual arousal in the male rats

Effects of two models of chronic stress were studied in adult male rats with inherited stress-induced arterial hypertension (ISIAH) and in Wistar rats. Intact males of both rat strains demonstrated a similar behavioural and hormonal activation in sexual arousal. Prepubertal chronic stress decreased the female-induced behavioural response and the effect depended on the character of stress and the animal genotype. No long-lasting effects of pre-pubertal stress on the plasma corticosterone level in males under sexual arousal were observed.     

Oxidative stress in pathogenesis of arterial hypertension in ISIAH rats]

The NO-synthase activity and the rate of NO production in the rat aortic wall and cerebellum were 2-1.5-fold higher in the ISIAH rats than in normotensive WAG rat strain. In contrast, the superoxide dismutase (SOD) activity was significantly reduced in the ISIAH rats. The blood level of reduced thiols was also much lower in the ISIAH rats. The findings suggest that oxidative stress may play a significant role in pathogenesis of stress-sensitive hypertension in the ISIAH rat strain.     

The electrical resistance of the lungs,intercostal muscles,and kidneys in hypertensive ISIAH rats

A comparative study of the bioelectrical impedance of normotensive and hypertensive animal tissues was carried out. It was found that the electrical resistance of kidneys, lungs, and intercostal muscles in rats with arterial hypertension (ISIAH strain) was significantly lower than in normotensive Wistar rats, which indicates that the volume of circulating blood and the total amount of fluid were increased in animals with arterial hypertension. The fact that the resistance of the conducting medium is decreased in arterial hypertension should be taken into account in the analysis of cardioelectric potentials on the body surface and electrocardiograms in conventional leads, as well as for the purposes of the development of heterogeneous torso models and for verification of recovery algorithms for electrical properties of chest tissues.     

A Search for Genetic Loci Responsible for Stress-Induced Arterial Hypertension in the ISIAH Rats

Hypertension is a widespread human disease caused by a complex interaction of a series of the genetic factors with both each other and the environmental conditions. In this study we aimed at determining the candidate genetic loci responsible for hypertension in the ISIAH rats and studying the dynamics of the relevant genetic and physiological mechanisms in rat ontogeny. The candidate genetic loci were identified from association of the microsatellite markers linked to these loci with arterial hypertension in rat F₂ hybrids exposed to stress. Two populations of F₂ hybrids of different age (3–4 and 6 months) were obtained by crossing hypertensive ISIAH and normotensive WAG rats. We present the results of cosegregation analysis for the following loci: the gene for the Na⁺, K⁺-ATPase alpha 1 subunit (Atp1a1), the endothelin-2 gene (Edn2), the low affinity nerve growth factor receptor gene (Lngfr), and a region of chromosome 10 marked with the D10Rat58 microsatellile located 3 cM away of the aldolase C gene (AldC). The results obtained allowed us to localize the genes responsible for the stress-induced arterial hypertension in the ISIAH rats to the Atp1a1locus (P < 0.05), chromosome 2 and to the Lngfr gene locus (P < 0.05), chromosome 10. The association of hypertensive status with the Lngfr gene was found only in young ISIAH rats whereas in adult rats of this strain, hypertension was associated with the Atp1a1locus.