Effects of Iron Nanoparticles Administration on Ischemia/Reperfusion Injury in Isolated Hearts of Male Wistar Rats.

Iron is an essential mineral participating in numerous biological processes in the organism under physiological conditions. However, it may be also involved in the pathological mechanisms activated in various cardiovascular diseases including myocardial ischemia/reperfusion (I/R) injury, due to its involvement in reactive oxygen species (ROS) production. Furthermore, iron has been reported to participate in the mechanisms of iron-dependent cell death defined as "ferroptosis". On the other hand, iron may be also involved in the adaptive processes of ischemic preconditioning (IPC). This study aimed to elucidate whether small amounts of iron may modify the cardiac response to I/R in isolated perfused rat hearts and their protection by IPC. Pretreatment of the hearts with iron nanoparticles 15 min prior to sustained ischemia (iron preconditioning, Fe-PC) did not attenuate post-I/R contractile dysfunction. Recovery of left ventricular developed pressure (LVDP) was significantly improved only in the group with combined pretreatment with iron and IPC. Similarly, the rates of contraction and relaxation [+/-(dP/dt)max] were almost completely restored in the group preconditioned with a combination of iron and IPC but not with iron alone. In addition, the severity of reperfusion arrhythmias was reduced only in the iron+IPC group. No changes in protein levels of "survival" kinases of the RISK pathway (Reperfusion Injury Salvage Kinase) were found except for reduced caspase 3 levels in both preconditioned groups. The results indicate that a failure to precondition rat hearts with iron may be associated with the absent upregulation of RISK proteins and the pro-ferroptotic effect manifested by reduced glutathione peroxidase 4 (GPX4) levels. However, combination with IPC suppressed the negative effects of iron resulting in cardioprotection.

Effect of iron oxide nanoparticles on vascular function and nitric oxide production in acute stress-exposed rats.

We investigated whether polyethylene glycol-coated Fe3O4 nanoparticles (IONs), acute stress and their combination modifies vascular functions, nitric oxide synthase (NOS) activity, mean arterial pressure (MAP) as well as hepcidin and ferritin H gene expressions in Wistar-Kyoto rats. Rats were divided into control, ION-treated rats (1 mg Fe/kg i.v.), repeated acute air-jet stress-exposed rats and IONs-and-stress co-exposed rats. Maximal acetylcholine (ACh)-induced and sodium nitroprusside (SNP)-induced relaxations in the femoral arteries did not differ among the groups. IONs alone significantly elevated the N?-nitro-L-arginine methyl ester (L-NAME)-sensitive component of ACh-induced relaxation and reduced the sensitivity of vascular smooth muscle cells to SNP. IONs alone also elevated NOS activity in the brainstem and hypothalamus, reduced NOS activity in the kidneys and had no effect in the liver. Acute stress alone failed to affect vascular function and NOS activities in all the tissues investigated but it elevated ferritin H expression in the liver. In the ION-and-stress group, NOS activity was elevated in the kidneys and liver, but reduced in the brainstem and hypothalamus vs. IONs alone. IONs also accentuated air-jet stress-induced MAP responses vs. stress alone. Interestingly, stress reduced ION-originated iron content in blood and liver while it was elevated in the kidneys. In conclusion, the results showed that 1) acute administration of IONs altered vascular function, increased L-NAME-sensitive component of ACh-induced relaxation and had tissue-dependent effects on NOS activity, 2) ION effects were considerably reduced by co-exposure to repeated acute stress, likely related to decrease of ION-originated iron in blood due to elevated decomposition and/or excretion.

High concentration of uric acid failed to affect endothelial function of small mesenteric arteries, femoral arteries and aortas from aged Wistar-Kyoto rats.

It is known that a high level of uric acid (UA) in plasma, hyperuricemia (HU), is associated with the increased risk of cardiovascular diseases (CVDs). Endothelial damage has been suggested as a potential mechanism involved in HU-induced CVDs, especially in patients with the accumulation of other cardiovascular risk factors. However, the role of UA in the pathogenesis of endothelial dysfunction is still a matter of debate. It is unclear whether UA is a causative risk factor in endothelial dysfunction, an inert marker or an endothelium-protective molecule with respect to its antioxidant properties. Of note, only a few studies have been conducted to investigate the effect of UA on vascular endothelium-dependent relaxation. Therefore, we have studied the acute in vitro effects of high UA concentrations on the endothelial function of arteries isolated from aged rats. Experiments were performed in small mesenteric arteries (SMAs), femoral arteries and thoracic aortas isolated from 68-week-old and 57-week-old male Wistar-Kyoto rats. Vascular reactivity was investigated in isometric conditions using the wire myograph and organ chamber. Acetylcholine (ACh) was used to investigate endothelium-dependent vasorelaxation. Then, UA was added to the myograph or organ chamber at 600 µmol/l (arteries from 68-week-old rats) or 1200 µmol/l (arteries from 57-week-old rats) and incubated for 1 h, and this was followed by determining the ACh concentration-response curve. UA had no significant effect on ACh-induced vasorelaxation and pD2 values in all investigated groups. Likewise, no significant differences in noradrenaline- (SMAs), serotonin- (femoral arteries) and phenylephrine-induced (aortas) vasoconstriction were observed after UA pre-incubation. In conclusion, high concentrations of UA administered acutely failed to affect endothelial function and did not provoke endothelial dysfunction in resistant mesenteric arteries, medium-sized and large arteries from aged rats.

Corrigendum to "(-)-Epicatechin Prevents Blood Pressure Increase and Reduces Locomotor Hyperactivity in Young Spontaneously Hypertensive Rats".

[This corrects the article DOI: 10.1155/2016/6949020.].

(-)-Epicatechin Prevents Blood Pressure Increase and Reduces Locomotor Hyperactivity in Young Spontaneously Hypertensive Rats.

This study investigated the effects of subchronic (-)-epicatechin (Epi) treatment on locomotor activity and hypertension development in young spontaneously hypertensive rats (SHR). Epi was administered in drinking water (100 mg/kg/day) for 2 weeks. Epi significantly prevented the development of hypertension (138 ± 2 versus 169 ± 5 mmHg, p < 0.001) and reduced total distance traveled in the open-field test (22 ± 2 versus 35 ± 4 m, p < 0.01). In blood, Epi significantly enhanced erythrocyte deformability, increased total antioxidant capacity, and decreased nitrotyrosine concentration. In the aorta, Epi significantly increased nitric oxide (NO) synthase (NOS) activity and elevated the NO-dependent vasorelaxation. In the left heart ventricle, Epi increased NOS activity without altering gene expressions of nNOS, iNOS, and eNOS. Moreover, Epi reduced superoxide production in the left heart ventricle and the aorta. In the brain, Epi increased nNOS gene expression (in the brainstem and cerebellum) and eNOS expression (in the cerebellum) but had no effect on overall NOS activity. In conclusion, Epi prevented the development of hypertension and reduced locomotor hyperactivity in young SHR. These effects resulted from improved cardiovascular NO bioavailability concurrently with increased erythrocyte deformability, without changes in NO production in the brain.

Blood pressure regulation in stress: focus on nitric oxide-dependent mechanisms.

Stress is considered a risk factor associated with the development of various civilization diseases including cardiovascular diseases, malignant tumors and mental disorders. Research investigating mechanisms involved in stress-induced hypertension have attracted much attention of physicians and researchers, however, there are still ambiguous results concerning a causal relationship between stress and long-term elevation of blood pressure (BP). Several studies have observed that mechanisms involved in the development of stress-induced hypertension include increased activity of sympathetic nervous system (SNS), glucocorticoid (GC) overload and altered endothelial function including decreased nitric oxide (NO) bioavailability. Nitric oxide is well known neurotransmitter, neuromodulator and vasodilator involved in regulation of neuroendocrine mechanisms and cardiovascular responses to stressors. Thus NO plays a crucial role in the regulation of the stress systems and thereby in the BP regulation in stress. Elevated NO synthesis, especially in the initial phase of stress, may be considered a stress-limiting mechanism, facilitating the recovery from stress to the resting levels via attenuation of both GC release and SNS activity as well as by increased NO-dependent vasorelaxation. On the other hand, reduced levels of NO were observed in the later phases of stress and in subjects with genetic predisposition to hypertension, irrespectively, in which reduced NO bioavailability may account for disruption of NO-mediated BP regulatory mechanisms and accentuated SNS and GC effects. This review summarizes current knowledge on the role of stress in development of hypertension with a special focus on the interactions among NO and other biological systems affecting blood pressure and vascular function.

Lack of reactive oxygen species deteriorates blood pressure regulation in acute stress.

This study investigated the contribution of reactive oxygen species (ROS) to blood pressure regulation in conscious adult male Wistar rats exposed to acute stress. Role of ROS was investigated in rats with temporally impaired principal blood pressure regulation systems using ganglionic blocker pentolinium (P, 5 mg/kg), angiotensin converting enzyme inhibitor captopril (C, 10 mg/kg), nitric oxide synthase inhibitor L-NAME (L, 30 mg/kg) and superoxide dismutase mimeticum tempol (T, 25 mg/kg). Mean arterial pressure (MAP) was measured by the carotid artery catheter and inhibitors were administered intravenously. MAP was disturbed by a 3-s air jet, which increased MAP by 35.2+/-3.0 % vs. basal MAP after the first exposure. Air jet increased MAP in captopril- and tempol-treated rats similarly as observed in saline-treated rats. In pentolinium-treated rats stress significantly decreased MAP vs. pre-stress value. In L-NAME-treated rats stress failed to affect MAP significantly. Treatment of rats with P+L+C resulted in stress-induced MAP decrease by 17.3+/-1.3 % vs. pre-stress value and settling time (20.1+/-4.2 s). In P+L+C+T-treated rats stress led to maximal MAP decrease by 26.4+/-2.2 % (p<0.005 vs. P+L+C) and prolongation of settling time to 32.6+/-3.3 s (p<0.05 vs. P+L+C). Area under the MAP curve was significantly smaller in P+L+C-treated rats compared to P+L+C+T-treated ones (167+/-43 vs. 433+/-69 a.u., p<0.008). In conclusion, in rats with temporally impaired blood pressure regulation, the lack of ROS resulted in greater stress-induced MAP alterations and prolongation of time required to reach new post-stress steady state.

Omega-3 fatty acids reduce lipopolysaccharide-induced abnormalities in expression of connexin-40 in aorta of hereditary hypertriglyceridemic rats.

Omega-3 fatty acids (omega3FA) are known to reduce hypertriglyceridemia- and inflammation-induced vascular wall diseases. However, mechanisms of their effects are not completely clear. We examined, whether 10-day omega3FA diet can reduce bacterial lipopolysaccharide-induced changes in expression of gap junction protein connexin40 (Cx40) in the aorta of hereditary hypertriglyceridemic (hHTG) rats. After administration of a single dose of lipopolysaccharide (LPS, 1 mg/kg, i.p.) to adult hHTG rats, animals were fed with omega3FA diet (30 mg/kg/day) for 10 days. LPS decreased Cx40 expression that was associated with reduced acetylcholine-induced relaxation of aorta. Omega3FA administration to LPS rats had partial anti-inflammatory effects, associated with increased Cx40 expression and improved endothelium dependent relaxation of the aorta. Our results suggest that 10-day omega3FA diet could protect endothelium-dependent relaxation of the aorta of hHTG rats against LPS-induced damage through the modulation of endothelial Cx40 expression.

Effect of maturation on the resistance of rat hearts against ischemia. Study of potential molecular mechanisms.

Reduced tolerance to ischemia/reperfusion (IR) injury has been shown in elder human and animal hearts, however, the onset of this unfavorable phenotype and cellular mechanisms behind remain unknown. Moreover, aging may interfere with the mechanisms of innate cardioprotection (preconditioning, PC) and cause defects in protective cell signaling. We studied the changes in myocardial function and response to ischemia, as well as selected proteins involved in "pro-survival" pathways in the hearts from juvenile (1.5 months), younger adult (3 months) and mature adult (6 months) male Wistar rats. In Langendorff-perfused hearts exposed to 30-min ischemia/2-h reperfusion with or without prior PC (one cycle of 5-min ischemia/5-min reperfusion), we measured occurrence of reperfusion-induced arrhythmias, recovery of contractile function (left ventricular developed pressure, LVDP, in % of pre-ischemic values), and size of infarction (IS, in % of area at risk size, TTC staining and computerized planimetry). In parallel groups, LV tissue was sampled for the detection of protein levels (WB) of Akt kinase (an effector of PI3-kinase), phosphorylated (activated) Akt (p-Akt), its target endothelial NO synthase (eNOS) and protein kinase Cepsilon (PKCepsilon) as components of "pro-survival" cascades. Maturation did not affect heart function, however, it impaired cardiac response to lethal IR injury (increased IS) and promoted arrhythmogenesis. PC reduced the occurrence of malignant arrhythmias, IS and improved LVDP recovery in the younger animals, while its efficacy was attenuated in the mature adults. Loss of PC protection was associated with age-dependent reduced Akt phosphorylation and levels of eNOS and PKCepsilon in the hearts of mature animals compared with the younger ones, as well as with a failure of PC to upregulate these proteins. Aging-related alterations in myocardial response to ischemia may be caused by dysfunction of proteins involved in protective cell signaling that may occur already during the process of maturation.

The effect of omega-3 fatty acids on expression of connexin-40 in Wistar rat aorta after lipopolysaccharide administration.

Connexin (Cx)-channels can represent one of targets of omega-3 fatty acids (n-3 PUFA) in protection of cardiovascular system against injury. We investigated the anti-inflammatory effect of 10-day n-3 PUFA intake (30 mg/kg/day for 10 days) on expression of Cx40 isoform in the aorta of Wistar rats injected with a single dose of lipopolysaccharide (LPS, 1 mg/kg, i.p.). LPS resulted in up-regulation of Cx40 expression in the aorta associated with reduced endothelium-dependent relaxation. LPS increased levels of inflammatory markers C-reactive protein and malondialdehyde in circulation as well as NOS activity and CD68 expression in aortic tissue indicating presence of moderate inflammation. N-3 PUFA supplementation decreased expression of both Cx40 and CD68 in aortic tissue and suppressed concentrations of C-reactive protein and malondialdehyde of endotoxemic rats. N-3 PUFA did not improve NO-dependent relaxation of aorta and NOS activity in LPS rats. The results indicate the involvement of Cx40 in development of LPS-induced endothelium-dependent functional impairment of the aorta and partial health benefits of n-3 PUFA diet associated with improved Cx40 expression.

Short-term administration of alibernet red wine extract failed to affect blood pressure and to improve endothelial function in young normotensive and spontaneously hypertensive rats.

As wine polyphenols were shown to possess many positive effects in mammals, including improvement of vascular function, this study investigated the effect of the Slovak Alibernet red wine extract (AWE) on blood pressure and vascular function in young normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats. Six weeks old, male, WKY and SHR were treated with AWE for three weeks at the dose of 24.2 mg/kg/day. Blood pressure (BP), determined by tail-cuff plethysmography, was significantly elevated in SHR vs. WKY and AWE failed to affect it. Lipid peroxidation was evaluated by determination of thiobarbituric acid-reactive substances. Vascular function was assessed in rings of the femoral artery using Mulvany-Halpern's myograph. Maximal endothelium-dependent acetylcholine (ACh)-induced relaxation was reduced in control SHR vs. WKY rats by approximately 9.3 %, which was associated with a significant decrease of its NO-independent component. AWE failed to affect maximal ACh-induced relaxation, both its NO-dependent and independent components, compared to controls of the same genotype. AWE however reduced lipid peroxidation in the left ventricle of both WKY and SHR and in the liver of SHR. In conclusion, three-week administration of AWE failed to reduce BP and to improve endothelial function in the femoral arteries of both genotypes investigated.

Endothelial dysfunction in femoral artery of the hypertensive rats is nitric oxide independent.

This study examined nitric oxide (NO) production, oxidative load and endothelium-dependent relaxation (NO-dependent and NO-independent) in adult male borderline hypertensive (BHR) and spontaneously hypertensive (SHR) rats as compared to normotensive Wistar-Kyoto (WKY) rats. Systolic blood pressure (BP) was determined by tail-cuff. NO production was determined by conversion of [(3)H]-L-arginine. Conjugated dienes (CD) and concentrations of thiobarbituric acid-reactive substances (TBARS) were measured for assessment of oxidative load. Vascular function was investigated in rings of the femoral artery (FA) using a wire myograph. BP of WKY, BHR and SHR was 106+/-2, 143+/-3 and 191+/-3 mm Hg, respectively (p<0.01 for each). Significant left ventricle (LV) hypertrophy and elevated levels of CD and TBARS in the LV were present in BHR and SHR as compared to WKY. NO production was elevated significantly in the aorta of BHR and SHR vs. WKY as well as in the LV of SHR vs. WKY. Acetylcholine (ACh)-induced relaxation of the FA was reduced significantly in both BHR and SHR vs. WKY. The NO-dependent component of ACh-induced relaxation had increasing tendency in hypertensive groups and it correlated positively with BP. The NO-independent component of vasorelaxation was reduced significantly in BHR and SHR vs. WKY and it correlated negatively with BP. In conclusion, the results showed that endothelial dysfunction in the experimental model of borderline hypertensive and hypertensive rats is NO-independent. The results suggest that borderline hypertension represents a risk of other cardiovascular disorders which is qualitatively similar to that of fully developed hypertension.

Impaired cardiac ischemic tolerance in spontaneously hypertensive rats is attenuated by adaptation to chronic and acute stress.

Chronic hypertension may have a negative impact on the myocardial response to ischemia. On the other hand, intrinsic ischemic tolerance may persist even in the pathologically altered hearts of hypertensive animals, and may be modified by short- or long-term adaptation to different stressful conditions. The effects of long-term limitation of living space (ie, crowding stress [CS]) and brief ischemia-induced stress on cardiac response to ischemia/reperfusion (I/R) injury are not yet fully characterized in hypertensive subjects. The present study was designed to test the influence of chronic and acute stress on the myocardial response to I/R in spontaneously hypertensive rats (SHR) compared with their effects in normotensive counterparts. In both groups, chronic, eight-week CS was induced by caging five rats per cage in cages designed for two rats (200 cm(2)/rat), while controls (C) were housed four to a cage in cages designed for six animals (480 cm(2)/rat). Acute stress was evoked by one cycle of I/R (5 min each, ischemic preconditioning) before sustained I/R in isolated Langendorff-perfused hearts of normotensive and SHR rats. At baseline conditions, the effects of CS were manifested only as a further increase in blood pressure in SHR, and by marked limitation of coronary perfusion in normotensive animals, while no changes in heart mechanical function were observed in any of the groups. Postischemic recovery of contractile function, severity of ventricular arrhythmias and lethal injury (infarction size) were worsened in the hypertrophied hearts of C-SHR compared with normotensive C. However, myo-cardial stunning and reperfusion-induced ventricular arrhythmias were attenuated by CS in SHR, which was different from deterioration of I/R injury in the hearts of normotensive animals. In contrast, ischemic preconditioning conferred an effective protection against I/R in both groups, although the extent of anti-infarct and anti-arrhythmic effects was lower in SHR. Both forms of stress may improve the altered response to ischemia in hypertensive subjects. In contrast to short-term preconditioning stress, chronic psychosocial stress was associated with a higher risk of lethal arrhythmias and contractile failure in normotensive animals exposed to an acute ischemic challenge.

[Assessment of vascular reactivity by wire myograph]. / Stanovenie cievnej reaktivity pomocou drôtikového myografu.

This paper describes the methodology and application of a wire myograph which has been used for the measurement of vascular reactivity. In an earlier years (pre-1970s) most of the information about the mechanical, morphological and pharmacological properties of vascular smooth muscle was confined only to larger arteries (mainly aorta). Whereas information about smaller arteries was purely inferred from perfusion experiments and histological examination. However, after mid-1970s Prof. Mulvany and Prof. Halpern developed and introduced an astonishing technique, a wire myography, to study the contractile responses of an isolated small resistance arteries (approximately 100-300 microm in internal diameter). This work describes some of the principles used in the investigation of the vessels, based on the use of the small vessel dual wire myograph. A dual myograph allows us simultaneous testing of two vessels. The technique allows segments of small arteries to be mounted as the ring preparations to the myograph chamber, and providing measurements of isometric responses. On the other hand, there are other techniques including an isobaric and isotonic mounting of arteries have been developed to date. The myograph has been used for the investigation of a variety of small and larger arteries and other tubular structures from a wide range of species. In the second part of this report we show an experimental example concerning measurement of endothelial functionality by technique described therein before.

[Endothelial (dys)function in the experimental model of primary hypertension]. / Endotelová (dys)funkcia v experimentálnom modeli esenciálnej hypertenzie.

A number of vascular diseases, including hypertension, are characterised by endothelial dysfunction caused by alterations in the production and action of the endothelium-derived relaxing (EDRFs) and/or endothelium-derived contracting (EDCFs) factors. The spontaneously hypertensive rat (SHR) is one of the most widely studied animal models for human essential hypertension. Several similarities between human primary hypertension and hypertension in the SHR have been pointed out in both the pathophysiology and the clinical course of the hypertensive disease. In human hypertension as well as in SHR, endothelium-dependent relaxation may be attenuated and this endothelial dysfunction contributes to the increased peripheral resistance. However, various results concerning endothelium-dependent relaxation, including impairment, no change and improvement have been reported in experimental hypertension. Endothelial dysfunction in hypertension has been linked to decrease in NO bioavailability, reflecting the impaired generation of NO and/or the enhanced inactivation of NO by reactive oxygen species. There is evidence that increased vascular oxidative stress is present in SHR. Thus, it has been proposed that oxidative inactivation of NO may account for the endothelial dysfunction seen in SHR. On the other hand, several studies demonstrate elevated basal NO synthesis in SHR rats which may be an adapting mechanism, preventing them from excessive blood pressure elevation. However, the role of NO in hypertension in SHR and in humans remains still controversial. We hypothesize that the vascular bed studied, the effect of age as well as methodological aspects, such as "precontraction" with different vasoconstrictors as well as antioxidants added to the solution for determination of the vasoreactivity may contribute to the discrepancies among studies. Nevertheless, the involvement of endothelial function in hypertension remains subject of debate and further research is needed to complete our knowledge on the role of NO, reactive oxygen species and other endothelial factors in the regulation of vascular and cardiac function.

Modulation of connexin-43 by omega-3 fatty acids in the aorta of old spontaneously hypertensive rats.

Hypertension alters expression of connexin-43 (Cx43) in cardiovascular system. The aim of the study was to investigate the effect of omega-3 polyunsaturated fatty acids (30 mg/day for 2 months) on expression of Cx43 in the aorta of 1-year-old male spontaneously hypertensive rats (SHR). Spatial distribution and expression of Cx43 in aortic wall of SHR and age-matched Lewis rats were determined by immunofluorescent method and Western blot. NO synthase (NOS) activity and endothelium-dependent relaxation of the aorta were measured as well. Immunofluorescent pattern of Cx43 was identified in endothelial and smooth muscle cells of the aorta of all experimental groups studied. However, local decrease in the number and intensity of fluorescent spots and reduced phosphorylation of Cx43 were observed in SHR in contrast to normotensive LEW. Omega-3 fatty acid diet increased Cx43 immunolabeling in endothelium and media of SHR comparing to untreated ones. Parallel, 3-fatty acids significantly elevated phosphorylation of Cx43 in the aorta of SHR (p<0.001). Despite the omega-3 fatty acids reduced blood pressure and stimulated aortic NOS activity in SHR, endothelium-dependent relaxation of the aorta did not significantly change. Results indicate that the aorta of old SHR might partially benefit from 3-PUFA supplementation due to increased Cx43 phosphorylation, NOS activity and decreased blood pressure.

Ultrastructural characteristics of aortic endothelial cells in borderline hypertensive rats exposed to chronic social stress.

Genetic predisposition and social stress may represent important risk factors in etiology of hypertension associated with endothelial dysfunction. Perturbations of endothelial structural integrity are also critical for the pathogenesis of vascular diseases. We examined effect of chronic social stress on structure of aortic endothelium in borderline hypertensive (BHR) and normotensive Wistar rats. Male BHR - offspring of Wistar mothers and SHR fathers and age-matched W were exposed to 6-week crowding stress (5 rats/cage, 200 cm2/rat). Aortic tissue was processed for electron microscopy and NO synthase activity measurement. Crowding stress significantly increased blood pressure in BHR compared to basal values (140+/-3 mm Hg vs. 130+/-3 mm Hg, p<0.05) and reduced enzyme activity by 37 % (p<0.01) in the aorta of BHR. Local slight structural alterations of endothelium were found in non-stressed BHR (p<0.001) when compared with Wistar rats. Chronic stress caused marked (p<0.005) subcellular injury of endothelial cells in aorta of BHR characterized by mitochondrial damage, presence of vacuoles, increased number of lysosomes, Weibel-Palade bodies, changes of intercellular connections and local disruption of endothelium, while only slight changes were seen in Wistar rats. Results suggest increased sensitivity of aortic endothelium of BHR to chronic crowding that may contribute to acceleration of arterial dysfunction.

Reduced connexin-43 expression in the aorta of prehypertensive rats.

Genetic component represents an important factor in the development of hypertension, which is known to be associated with changes in expression of vascular gap junction protein connexin 43 (Cx43). The aim of the study was to examine the distribution and expression of Cx43 in the aortic endothelium of adult normotensive Wistar rats (W), borderline hypertensive rats (BHR) and spontaneously hypertensive rats (SHR). Rings of the thoracic aorta were processed for immunofluorescence and Western blot analysis of endothelial Cx43 and for electron microscopy. Both, BHR and SHR exhibited significantly increased blood pressure vs. W (132+/-2 mm Hg and 185+/-3 mm Hg vs. 110+/-2 mm Hg). Reduced Cx43 immunofluorescence was observed in the endothelium of BHR and these alterations were more pronounced in SHR. Western blot analysis showed significant suppression of Cx43 expression in the aorta of both BHR (p<0.05) and SHR (p<0.001) vs. W. Electron microscopy revealed local subcellular alterations of interendothelial connections in BHR including extended tight junctions. These alterations were more frequent and marked in SHR. The results indicate that connexin 43 expression is reduced in the aortic endothelium already in prehypertensive period, which may affect cell-to-cell communication and thus participate in acceleration of hypertensive disease.

[The role of endothelium and nitric oxide in the regulation of vascular tone]. / Uloha endotelu a oxidu dusnatého v regulácii cievneho tonusu.

Vascular system is a large complex of tubes with different diameters which are able to perceive changes of endogenous milieu, to integrate and modulate signals of intercellular communication and to respond and adapt by a local production of different kinds of mediators affecting vascular structure and function. For a long time, it has been assumed that the main determinant of vasomotor function was the nervous system and the monolayer of endothelial cells was only a physical barrier between the vessel wall and blood. However, the first publications in 1960s and 70s indicated that endothelium is not only a passive barrier. Endothelium features autocrine, paracrine and endocrine activities. Vascular endothelium plays an important role in the regulation of vascular tone, blood pressure and blood flow beside central regulation of nervous system. The existence of endothelium-derived relaxing factor (EDRF) was found out by Furchgott and Zawadzki (1980) who showed that acetylcholine induced relaxation of the rabbit aorta only in the presence of intact endothelium. Nowadays, nitric oxide (NO), previously known as EDRF, is considered one of the crucial endothelium-derived vasorelaxing substances participating in the regulation of basal vascular tone, vascular resistance and thus in the regulation of blood pressure. Arterial bed is dilated continuously as a consequence of constant production of NO. Any damage of endothelium modifies regulatory functions of endothelial cells. These conditions are characterised as endothelial dysfunction associated with imbalance between vasodilating and vasoconstricting factors, pro- and anticoagulation factors and factors stimulating and inhibiting growth and proliferation of cells. However, cellular mechanisms which are involved in the development of endothelial dysfunction, are still not well-known.

Crowding-induced alterations in vascular system of Wistar-Kyoto rats: role of nitric oxide.

The aim of this study was to determine the effect of chronic crowding on the cardiovascular system of Wistar-Kyoto (WKY) rats. Rats were randomly divided into the control (480 cm(2) per rat) or crowded (200 cm(2) per rat) group for eight weeks. Body weight, blood pressure (BP), heart rate and plasma nitrate/nitrite levels of the crowded rats were not different from controls at the end of the experiment. Plasma corticosterone exhibited an increasing trend (5.7+/-1.8 vs. 12.6+/-3.7 ng/ml, p=0.08) while blood glucose was significantly reduced in the crowded rats in comparison with the controls. Nitric oxide (NO) synthase activity and nitrate/nitrite levels of the crowded rats were significantly elevated in the aorta by 80 % and 20 %, respectively, but unchanged in the left ventricle. Moreover, acetylcholine-induced relaxation was significantly increased in the crowded rats in both the femoral artery (61+/-5 % vs. 76+/-5 %, p<0.001) and mesenteric artery (51+/-6 % vs. 72+/-7 %, p<0.001). In conclusion, results suggest that chronic crowding may increase vasorelaxation and vascular NO production in normotensive rats. This may be considered as an adapting mechanism preventing the development of the stress-related elevation of BP. Additionally, results also suggest caution in the housing of rats because an inappropriate crowding may affect results of the experiment significantly.