Increase in the concentration of sEH protein in renal medulla of ISIAH rats with inherited stress-induced arterial hypertension

The concentration of soluble epoxide hydrolase (sEH) protein was studied in renal medulla of adult rats from hypertensive ISIAH strain and normotensive WAG strain. The sEH is a key enzyme in metabolism of epoxyeicosatrienoic acids capable of activating endothelial NO-synthase and nitrogen oxide formation, and therefore being vasodilators. An increase in the sEH protein concentration (that we found) allows one to assume that the oxidative stress is increased in the renal medulla of hypertensive rats, and the bloodflow is decreased.     

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 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.     

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.     

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.     

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.     

Noradrenaline synthesis during the first week of life and development of inherited stress-induced arterial hypertension in rats

Increasing of the noradrenaline synthesis with daily i.p. administration of synthetic noradrenaline precursor DL-Threo on the 21-25th day of life of the rats with inherited stress-induced arterial hypertension (ISIAH) resulted in a drop of basal and stress-induced blood pressure in adult animals with no changes in response of the hypothalamic-pituitary-adrenocortical system (HPAS). Reduction of the noradrenaline synthesis with daily i.p. administration of dopamine-hydroxylase inhibitor FLA-57 in 21-25th day old Wistar rats induced no arterial hypertension in adults but decreased their adrenocortical response to emotional stress. Noradrenaline deficit in the brain structures on the 4th week of life in rats seems to be associated with arterial hypertension only in presence of genetic defect determining this pathology. Changes in adult HPAS function due to shortage of noradrenaline in the brain in the end of the 1st month of life do not depend on hypertension.     

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).     

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.     

Brain adrenoreceptors in rats with inherited arterial hypertension due to emotional stress

For the study of genetic and physiological mechanisms of inherited stress-sensitive arterial hypertension, specific binding of ligands of alpha 1-, alpha 2- and beta-adrenoceptors was measured in 2 strains of rats: Wistar normotensive and ISSAH rats (rats with inherited stress-sensitive arterial hypertension). The maximal binding sites (Bmax) and apparent dissociation constants (Kd) were studied with the alpha 1-adrenergic antagonist 3H-prazosin, alpha 2-adrenergic agonist 3H-clonidine and 3H-dihydroalprenolol, a beta 1-receptor antagonist. Four brain regions were investigated: frontal cortex, hypothalamus, pons and medulla oblongata. In comparison with normotensive controls, hypertensive rats had significantly greater density of the alpha 1-adrenoceptors in the medulla oblongata. However, the number of hypothalamic alpha 1-adrenoceptors was significantly reduced in these animals. The same significantly lower alpha 2-adrenoreceptor density was found in the hypothalamus and the pons, and lower, beta-adrenoceptors density in the medulla oblongata. It was concluded that brain adrenoceptors are involved in the mechanisms of development of inherited stress-sensitive hypertensive syndrome.     

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.     

Functional activity of the structures of the medulla oblongata in rats with arterial hypertension of renal origin (histoenzymological research)

A quantitative histochemical study of succinate dehydrogenase (SDH) and NADH-dehydrogenase (NADH-D) activity in medulla oblongata structures was accomplished in rats with arterial renovascular hypertension of the "2 kidneys-2 clips" type lasting 5 months. The systolic arterial blood pressure measured by the tail-cuff method was 179 +/- 4 mm Hg in hypertensive rats versus 108 +/- 3 mm Hg in control. There was a significant elevation of SDH activity in the ventral reticular and commissural nuclei, while in the neurons of the vagus dorsal and ambiguous nuclei it was lowered. NADH-D activity was significantly increased in the neuropil of the hypoglossal nerve nucleus and reduced in its neurons. The general trend was also revealed toward reduction of the maximal and elevation of the minimal activities in other nuclei. These metabolic alterations reflect changes in the functional activity of vasomotor and other structures of the medulla oblongata in renovascular hypertension.     

Comparative analysis of conditioned passive avoidance retention in rats with different forms of inherited arterial hypertension

Comparing behavioral traits of anxiety in elevated plus-maze and retention of passive avoidance response in two rat strains with hereditary arterial hypertension ISIAH (inherited stress induced arterial hypertension) and SHR (spontaneously hypertensive rats) has shown the following. The SHR rats demonstrate impairment in retrieval of passive avoidance, hyperactivity and low anxiety. ISIAH rats showned better avoidance performance, average level of anxiety and activity. The interdependence of two pathologies: hypertension and memory impairment is discussed.     

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.