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.     

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.     

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.     

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.     

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.     

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.     

Endocrine-metabolic relations in rats with genetic arterial hypertension

Levels of triiodothyronine, thyroxine, insulin, glucose and free fatty acids in the blood; contents of adrenaline, noradrenaline in adrenals and glycogen in the liver; activity of phenylethanolamine-N-methyltransferase in adrenals, hexokinase and glucose-6-phosphatase in the liver were studied in male Wistar rats and rats with inherited stress-induced arterial hypertension /ISIAH/. It was found that genetically caused rise of hypophyseal-thyroid systems activity in ISIAH-rats leads to a decrease of insulin blood level, activation of lipolysis and breach of glucose tolerance.     

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.     

Model of emotional stress in rats

A new experimental rat model for suppression of release of arginine vasopressin (AVP) was evaluated. Release of AVP is potentiated by physiologic stimuli, but is suppressed by emotional stress. Rats were exposed to the aggressive behavior of other rats injected with 6-hydroxydopamine hydrochloride (6-OHDA) in both lateral ventricles and subjected to a pain stimulus applied to the tail. To ascertain whether emotional stress is induced by use of this method, plasma corticosterone, glucose, and AVP concentrations were measured in the stressed group of rats (n = 8) placed near a group of aggressive (fighting) rats. Characteristic changes in behavior, significant increases in plasma corticosterone and glucose values, and lack of increase in plasma AVP concentration in stressed rats confirmed that they experienced emotional stress. This new model meets the experimental requirements for suppression of AVP release in rats.     

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.     

Adrenaline-induced damage to the myocardium in rats with genetically determined arterial hypertension

Genetically hypertensive and normotensive rats were subjected to acute myocardial injury by a single subcutaneous injection of adrenaline (0.5 mg/100 g bw). The animals were sacrificed one day later. The lesions showed the signs of focal coagulative necrosis and intracellular myocytolysis. The damaged cardiomyocytes with high sarcolemmal permeability for blood plasma proteins were more widespread in the hypertensive versus normotensive rats. Intracellular myocytolysis, which is not associated with alterations in the cell membrane, was found in both experimental groups at an equal rate. The data agree with the concepts of alterations in biological membranes in genetically determined arterial 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).     

Impaired left ventricular filling due to right-to-left ventricular interaction in patients with pulmonary arterial hypertension

The aim of this study was to investigate the contribution of direct right-to-left ventricular interaction to left ventricular filling and stroke volume in 46 patients with pulmonary arterial hypertension (PAH) and 18 control subjects. Stroke volume, right and left ventricular volumes, left ventricular filling rate, and interventricular septum curvature were measured by magnetic resonance imaging and left atrial filling by transesophageal echocardiography. Stroke volume, left ventricular end-diastolic volume, and left ventricular peak filling rate were decreased in PAH patients compared with control subjects: 28 +/- 13 vs. 41 +/- 10 ml/m(2) (P < 0.001), 46 +/- 14 vs. 61 +/- 14 ml/m(2) (P < 0.001), and 216 +/- 90 vs. 541 +/- 248 ml/s (P < 0.001), respectively. Among PAH patients, stroke volume did not correlate to right ventricular end-diastolic volume or mean pulmonary arterial pressure but did correlate to left ventricular end-diastolic volume (r = 0.62, P < 0.001). Leftward interventricular septum curvature was correlated to left ventricular filling rate (r = 0.64, P < 0.001) and left ventricular end-diastolic volume (r = 0.65, P < 0.001). In contrast, left atrial filling was normal and not correlated to left ventricular end-diastolic volume. In PAH patients, ventricular interaction mediated by the interventricular septum impairs left ventricular filling, contributing to decreased stroke volume.     

Somatosympathetic reflex in rats with various models of arterial hypertension

Spontaneous and reflex activities of sympathetic nerve were compared in animals with arterial hypertension of different aetiology. Reflex discharges elicited by single-shock stimulation of afferent fibres were recorded. In acute experiences on anaesthetized rats with renovascular and spontaneous (SHR) model of arterial hypertension, electric basal and evoked activity (somatosympathetic reflex) in cervical sympathetic trunk were recorded. It is shown, that the spontaneous electric activity in sympathetic nerve of hypertensive rats is larger than spontaneous activity of normotensive control animals. The somatosympathetic reflex in hypertensive rats differs from that of control animals. In rats with renovascular model of hypertension, the reflex magnitude is reduced, and in the SHR the reflex is increased. Time characteristics of the reflex in hypertensive rats differed among them. It is suggested that functional activities of the brain stem in rats with different arterial hypertension model are unequal.     

Endocrine and lymphoid interrelations in rats with hereditary arterial hypertension

Functional state of the adrenals and structural organization of the thymus and lymph nodes in the rats with hereditary stress-induced arterial hypertension (HSIAH) have been investigated in the control and against the background of a prolonged staying under conditions of a moderate cold. In comparison with the initial population of Wistar rats, the test animals demonstrate an elevated level of corticosterone, decreased mass and size of the thymus, the size of the popliteal lymph nodes is increased at the expense of the structural components of the medulla. In 7 weeks of living in cold secretion of adrenal steroids in Wistar rats increases greatly and it is noticeably less in the HSIAH rats. Structural changes in the thymus are also insignificant, but reaction of the lymph nodes is important. Their size sharply diminishes at the expense of certain structural components of the medulla. A shift towards mature forms of the plasmocytic line cells takes place.