We hypothesized that hypertension-related myocardial remodeling characterized by hypertrophy and fibrosis might be accompanied by cell-to-cell gap junction alterations that may account for increased arrhythmogenesis. Intercellular junctions and expression of gap junction protein connexin-43 were analyzed in rat heart tissues from both spontaneous (SHR) and L-NAME model of hypertension. Isolated heart preparation was used to examine susceptibility of the heart to lethal ventricular fibrillation induced by low potassium perfusion. Ultrastructure observation revealed enhanced neoformation of side-to-side type while internalization of end-to-end type (intercalated disc-related) of gap junctions prevailed in the myocardium of rats suffering from either spontaneous or L-NAME-induced hypertension. In parallel, immunolabeling showed increased number of connexin-43 positive gap junctions in lateral cell membrane surfaces, particularly in SHR. Besides, focal loss of immunopositive signal was observed more frequently in hearts of rats treated with L-NAME. There was a significantly higher incidence of hypokalemia-induced ventricular fibrillation in hypertensive compared to normotensive rat hearts. We conclude that adaptation of the heart to hypertension-induced mechanical overload results in maladaptive gap junction remodeling that consequently promotes development of fatal arrhythmias., M. Fialová, K. Dlugošová, L. Okrouhlicová, F. Kristek, M. Manoach, N. Tribulová., and Obsahuje bibliografii a biblioigrafické údaje
We studied the effects of the H2S donor Na2S on the mean arterial blood pressure (MAP) and heart and breathing rates of anesthetized Wistar rats in the presence and absence of captopril. Bolus administration of Na2S (1-4 μmol/kg) into the right jugular vein transiently decreased heart and increased breathing rates; at 8-30 μmol/kg, Na2S had a biphasic effect, transiently decreasing and increasing MAP, while transiently decreasing heart rate and increasing and decreasing breathing rate. These results may indicate independent mechanisms by which H2S influences MAP and heart and breathing rates. The effect of Na2S in decreasing MAP was less pronounced in the presence of captopril (2 μmol/l), which may indicate that the renin-angiotensin system is partially involved in the Na2S effect. Captopril decreased H2S-induced NO release from S-nitrosoglutathione, which may be related to some biological activities of H2S. These results contribute to the understanding of the effects of H2S on the cardiovascular system., M. Drobná, A. Misak, T. Holland, F. Kristek, M. Grman, L. Tomasova, A. Berenyiova, S. Cacanyiova, K. Ondrias., and Obsahuje bibliografii
We evaluated the effects of N G -nitro-L-arginine methylester (L-NAME) (50 mg/kg/day) and 7-nitroindazole (7NI) (10 mg/kg/day) administered from 10th-16th week of age either individually or together on cardiovascular system of Wistar rats and SHR. Systolic blood pressure (sBP) was measured weekly by the plethysmographic method. For morphological studies, the animals (n=10) were perfused with a fixative (120 mm Hg), and thoracic aorta and carotid and co ronary arteries were processed for electron microscopy. For functional investigation (n=10), aortic rings were used in an or gan bath. In Wistar rats, L-NAME evoked an increase of sBP; hype rtrophy of the heart and arterial walls; an increase in cross-sectional areas (CSA) of endothelial cells (EC), muscle cells (SMC), extracellular matrix (ECM), and a decrease in acetylcholin e-induced endothelial-dependent relaxation (EDR). 7NI evoked sBP-independent hypotrophy of the heart and arterial walls, a decrease in CSA of EC and SMC without affecting the CSA of ECM, and a mild decrease in acetylcholine-induced EDR. 7NI and L-NAME administered together evoked lower effect on BP and trophicity of the heart and all arteries, and a similar de crease in acetylcholine-induced EDR compared to L-NAME alone. In SHR, 7NI did not evoke any effect on the studied parameters., F. Kristek, M. Drobna, S. Cacanyiova., and Obsahuje bibliografii
Structural changes of thoracic aorta (TA), carotid (CA) and iliac artery (IA) were assessed in Wistar and spontaneously hypertensive rats (SHR) aged 3, 17, and 52 weeks. Systolic blood pressure (sBP) was measured by plethysmography weekly. After perfusion fixation the arteries were processed for electron microscopy. The wall thickness (WT), cross-sectional area (CSA), inner diameter (ID), and WT/ID in all arteries and volume densities of endothelial cells (ECs), muscle cells (SMCs), and extracellular matrix (ECM) in TA were measured and their CSAs were calculated. In 3-week-old SHR compared to Wistar rats, sBP did not differ; in the TA, all parameters (WT, CSA, ID, WT/ID, CSA of SMCs, CSA of ECs, and CSA of ECM) were decreased; in CA, WT and CSA did not differ, ID was decreased, and WT/ID was increased; in IA, WT, CSA, and ID were increased. In 17- and 52-week-old SHRs, sBP and all parameters in all arteries were increased, only ID in IE in 52-week-old SHRs and CSA of ECs in the TA in 17-week-old SHRs did not change. Disproportionality between BP increase and structural alterations during ontogeny in SHR could reflect the flexibility of the arterial tree to the different needs of supplied areas.
Two exogenous NO donors were used to act as substitutes for impaired endogenous nitric oxide (NO) production due to inhibition of NO synthase in rats. Six weeks' lasting inhibition of NO synthase by NG-nitro-L-arginine methyl ester (L-NAME) induced stabilized hypertension. Simultaneously administered isosorbide-5-mononitrate did not prevent the development of hypertension. Molsidomine, administered concomitantly with L-NAME, significantly attenuated the BP increase. However, BP was still found to be moderately increased compared to the initial values. Remarkable alterations in the geometry of the aorta, carotid and coronary artery found in NO-deficient hypertension were prevented in rats administered L-NAME plus molsidomine at the same time. In spite of 6 weeks' lasting inhibition of NOS, the NOS activators acetylcholine and bradykinin induced BP decrease; the maximum hypotensive value did not differ from the values recorded in the controls or in animals treated with L-NAME plus molsidomine. Notably enough, the hypotension was similar to that found in rats administered L-NAME alone for six weeks. After NO synthase inhibition, Isosorbide-5-mononitrate does not substitute and molsidomine substitute only partially the impaired endogenous NO production., M. Gerová, F. Kristek., and Obsahuje bibliografii
Numerous studies concerning the cardiovascular system in SHR often yield controversial data. The background of this diversity has various roots, ranging from different vascular segments or areas studied up to the different age of experimental animals. Our study aimed to follow the BP as an integrated response of vascular system. This approach was justified since stabilized cardiac output in SHR was proved till 1 year of age. The groups of male SHR (aged 3, 5, 9, 17 and 52 weeks) and age-matched Wistar rats were used. Significant basal BP difference between SHR and Wistar rats was found at 9 weeks of age and continued till the age of 52 weeks, reaching 189.6±11.9 mm Hg in SHR and 117.3±6.9 mm Hg in Wistar rats (P<0.01). The significant difference in BP increase to two doses of noradrenaline (0.1μg and 1 μg) between SHR and control rats was also found at the age of 9 weeks. At 52 weeks the BP increment to two doses of noradrenaline was in SHR 19.7±2.0 mm Hg and 60.5±3.9 mm Hg and in Wistar rats 7.4±1.9 mm Hg and 40.5±3.2 mm Hg (P<0.01). The hypotensive response to acetylcholine (0.1 μg, 1 μg and 10 μ) in SHR was enhanced at 17 weeks of age only and this amplification persisted till the age of 52 weeks. In 52-week-old SHR the hypotensive response to three doses was 69.9±10.2 mm Hg, 87.5±11.8 mm Hg and 103.4±10.6 mm Hg, while in Wistar rats it was 37.4 4.2 mm Hg P<0.0), 62.3±3.5 mm Hg (P<0.01) and 73.5±2.8 mm Hg (P<0.05). In conclusion, the efficiency of cardiovascular system of SHR to respond to noradrenaline was already enhanced from 9 weeks of age, whereas the response to acetylcholine was not augmented before the age of 17 weeks., M. Gerová, F. Kristek., and Obsahuje bibliografii a bibliografické údaje
We studied the effects of long-term administration of molsidomine and pentaerythrityl tetranitrate (PETN) on the cardiovascular system of spontaneously hypertensive rats (SHR). One control and three experimental groups of 10-week-old animals were used: 1) control Wistar rats, 2) SHR, 3) SHR treated with molsidomine in tap water (100 mg/kg/day, by gavage), and 4) SHR treated with PETN in tap water (200 mg/kg/day, by gavage). After six weeks, the content of cGMP in platelets and NO synthase (NOS) activity in aortas were evaluated in the experimental groups. For morphological evaluation the rats were perfused at 120 mm Hg with a glutaraldehyde fixative and the arteries were processed for electron microscopy. Blood pressure and heart weight/body weight ratio (HW/BW) were increased in all experimental groups with respect to the controls. HW/BW was lower in the molsidomine group in comparison to both SHR and PETN-treated group. The platelet content of cGMP was increased and the activity of NOS in the aortas was decreased in the molsidomine and PETN-treated groups. Wall thickness and cross-sectional area of thoracic aorta, carotid artery and coronary artery were increased similarly in all experimental groups compared to the controls, but there were no differences among the experimental groups. We summarize that long-term administration of exogenous NO donors did not improve pathological changes of the cardiovascular system in SHR., F. Kristek, V. Fáberová, I. Varga., and Obsahuje bibliografii
The heart weight and the structure of coronary and carotid arteries were studied in NO-deficient hypertension. Wistar rats were administered L-NAME (50 mg/kg/day) in drinking water for a period of 8 weeks. The blood pressure and heart rate were recorded weekly. In one group of control and experimental animals the heart weight was assessed and the heart/body weight ratio (relative heart weight) was calculated. In the other group of control and experimental animals, the cardiovascular system was perfused by a fixative under constant perfusion pressure. The inner circumference and the wall thickness (tunica intima and tunica media) of the coronary (septal branch) and carotid artery were measured using light microscopy and the wall/diameter ratio was calculated. Inhibition of NO synthase induced a significant increase in blood pressure (187.2±4.2 mm Hg compared to 131.4±1.9 mm Hg in the controls, p<0.01). The heart rate decreased (334.4±7.0 beats/min compared to 352.6±4.1 beats/min in the controls, p<0.05). The heart weight increased in NO-deficient rats (132±0.08 g versus 1.10±0.03 g, p<0.05); the heart/body weight index increased remarkably (3.09±0.15 compared to 2.10±0.04 in the controls, p<0.01). Morphometry of the septal branch of the left coronary artery indicated a decrease of the inner circumference (664±24 /um versus 832±30 //m, p<0.01), the increased wall thickness (21.15±0.84 jtm compared to 12.47±0.62 Jim in the controls, p<0.01) and the remarkably changed wall/diameter ratio (1:10 versus 1:21 in the controls). Similar alterations were found in the carotid arteries: the inner circumference was decreased (2456±39 Jim versus 2732±66 /¿m, p<0.01), the wall thickness increased (45.14±0.41 jim compared to 26.08±1.23 fim, p<0.01) and the wall/diameter ratio was changed to 1:17 in comparison with 133 in the controls. In conclusion, cardiac hypertrophy and structural alterations of the coronary artery and carotid artery accompany NO-deficient hypertension.
Nitric oxide concentration in the periendothelial area of the femoral vein in anaesthetized dogs was measured directly with a catheter- protected porphyrinic sensor. A 2- to 4-fold increase occurred in the basal NO concentration of 90±12 nM after acetylcholine injection (1-1.5 ,wg/kg). A linear correlation was found between femoral artery blood flow and NO concentration in the periendothelial area of the femoral vein. Noradrenaline decreased NO levels below the detection limit of the porphyrinic sensor (10 nM).
• NO concentration was measured in the periendothelial area of the femoral artery by Malinski’s porphyrinic • NO sensor in seven anaesthetized dogs. The basal concentration was 154.2 ±5.6 nM and two-minute intraarterial infusions of acetylcholine (3-4 /tg/ml/min) or bradykinin (30 - 40 ng/ml/min) increased this value significantly to 204.3±16.4 and 266.5±16.4 nM (P<0.01), respectively. Inhibition of »NO synthase by L-NAME (50 mg/kg) declined the basal • NO concentration only to 137.2±3.3 nM (PcO.Ol). Subsequent administration of acetylcholine and bradykinin attenuated significantly the increase in • NO concentration. Surprisingly, both agonists still induced a significant increase of *NO concentration by 125.3±8.3 and 156.6±26.9 nM, respectively (PcO.Ol). One of the possible explanations may be that besides arginine-citrulline plus the • NO pathway other sources of • NO could be involved in the high level of • NO after • NO synthase blockade by L-NAME.