Jozef Török

Endothelium-dependent relaxation in rabbit aorta after cold storage

The extent of preservation of endothelial, smooth muscle and neurogenic function following cold storage was studied in rabbit thoracic aorta. Relaxation responses to acetylcholine and sodium nitroprusside were compared between fresh aortic rings and rings that had been stored in a refrigerator for 2-8 days at 4 degrees C. In fresh aortic rings, the addition of acetylcholine to precontracted vessels resulted in dose-dependent relaxation. The magnitude of relaxation was gradually decreased after 4-8 days of cold storage. Relaxation in response to sodium nitroprusside did not change. Following cold storage contractions of aortic rings in response to noradrenaline and phenylephrine were not reduced. Contractile responses induced by transmural nerve stimulation were gradually attenuated with the length of cold storage. Electron microscopy after 4 days showed partial damage of endothelial cells (slightly vacuolized mitochondria). After 8 days, endothelial cells were destroyed; only membranous material was present. The structure of smooth muscle cells was only partially changed even after 8 days. Sympathetic nerve endings on the 4th day were partially, but on the 8th day completely destroyed. These results suggest that after cold storage of rabbit aorta, the gradual reduction of endothelium-dependent relaxation is probably caused by a decrease in production of the endothelium-derived relaxing factor due to the destruction of endothelial cells.

Impaired Endothelial Function of Thoracic Aorta in Hereditary Hypertriglyceridemic Rats

Abstract: Objective—Hereditary hypertriglyceridemia (hHTG) in rats was found to be associated with metabolic abnormalities and elevation of blood pressure. There is controversy regarding the relation between hHTG and vascular function. The aim of this study was to determine the reactivity and accompanying structural changes in thoracic aorta from hereditary hypertriglyceridemic rats and hHTG rats that were given, for a long time, NG‐nitro‐l‐arginine methyl ester (L‐NAME) with and without simultaneous captopril treatment. Methods—Isolated rings of thoracic aorta were mounted in organ chambers for isometric tension recording or for measurement of endothelium‐dependent relaxation. Morphological changes of thoracic aorta (wall thickness, diameter) were measured using light microscopy. Results—Endothelium‐dependent relaxation (EDR) to acetylcholine (ACh, 10−5 M) was significantly attenuated in the hHTG group compared to control Wistar rats (59.3 ± 8.5% vs. 95.8 ± 6.5%, p < 0.001), but normalized after pretreatment with captopril. EDR to ACh was further inhibited in hHTG rats treated with L‐NAME (36.0 ± 2.3%, p < 0.001). Maximum residual relaxation was only partly restored with captopril treatment (72.4 ± 5.8%, p < 0.001). Hypertriglyceridemia did not significantly alter the sensitivity of the thoracic aorta to exogenous noradrenaline. The diameter/wall thickness (D/W) ratio in aortas of control Wistar rats averaged 16.25 ± 0.57. This ratio was significantly lower in hHTG rats (12.52 ± 0.38, p < 0.01) and was not altered after treatment with captopril. In the hHTG rats treated with L‐NAME, the D/W ratio was further significantly decreased (8.25 ± 0.30, p < 0.001). Simultaneous captopril treatment attenuated the decrement of this ratio (9.80 ± 0.75, p < 0.05). Conclusions—Results showed that hHTG is accompanied by functional and morphological alterations in the rat thoracic aorta. These changes in hHTG and in hHTG rats treated with L‐NAME could be, at least in part, protected by captopril treatment.

Developmental dynamics of endothelial and neurogenic control of canine thoracic aorta

The purpose of the study was to confront the range of endothelial relaxation and neurogenic contraction of the thoracic aorta in fetuses (1 week before birth), puppies (1, 2, 4 and 6 weeks old), and in adult dogs. Isometric tension of aortic rings was monitored in organ bath. Acetylcholine-induced dose-dependent relaxation of aortic rings precontracted by phenylephrine was pronounced already in fetuses and puppies and significantly larger than in adults. Indomethacin, a cyclooxygenase inhibitor, did not affect the magnitude of aortic relaxation to acetylcholine. Transmural nerve stimulation induced but very slight contractions of the thoracic aorta in fetuses, while in puppies the extent of contractions was increasing with increasing age, reaching its maximum in adults. Contractile responses of aortic rings induced by KCl were fully detectable in fetuses and puppies and increased with increasing age of the animals. Thus in ontogenesis, the extent of endothelium-dependent relaxation and neurogenic contraction of the thoracic aorta displayed an opposite trend. The acetylcholine-induced relaxation was fully operative already in fetuses and puppies and its extent was declining toward adulthood, whereas the neurogenic contraction was hardly detectable in fetuses, increasing in puppies, and showed the highest values in adults.

Beneficial effect of pentaerythrityl tetranitrate on functional and morphological changes in the rat thoracic aorta evoked by long-term nitric oxide synthase inhibition

The present study examined whether pentaerythrityl tetranitrate (PETN), a tolerance-devoid exogenous donor of nitric oxide (NO), could attenuate functional and morphological changes in the rat thoracic aorta evoked by 6-week NO synthase inhibition by NG-nitro-L-arginine methyl ester (L-NAME). Systolic blood pressure in L-NAME + PETN-treated rats (163 +/- 1 mm Hg) was significantly lower than in L-NAME-treated rats (172 +/- 2 mm Hg) but was still higher than in age-matched controls (126 +/- 2 mm Hg). Six weeks of treatment of rats with L-NAME significantly inhibited endothelium-dependent relaxation of the isolated thoracic aorta induced by acetylcholine. The inhibitory effect of L-NAME was entirely reversed by the simultaneous treatment with PETN. The enhancing effect of L-NAME on noradrenaline-induced contraction was antagonised by long-term treatment with PETN. Wall thickness, cross-sectional area and wall/diameter ratio of the thoracic aorta in L-NAME-treated rats were markedly increased. In the L-NAME + PETN-treated rats, the increment of these parameters was significantly lower. The results suggest that PETN administered to rats during development of NO-deficient hypertension prevented functional impairment and at the same time reduced structural changes in the thoracic aorta induced by long-term inhibition of NO synthase.

Diminished Contractile Responses of Isolated Conduit Arteries in Two Rat Models of Hypertension

Hypertension is accompanied by thickening of arteries, resulting in marked changes in their passive and active mechanical properties. The aim of this study was to demonstrate that the large conduit arteries from hypertensive individuals may not exhibit enhanced contractions in vitro, as is often claimed. Mechanical responses to vasoconstrictor stimuli were measured under isometric conditions using ring arterial segments isolated from spontaneously hypertensive rats, N(omega)-nitro-L-arginine methyl ester (L-NAME)-treated Wistar rats, and untreated Wistar rats serving as normotensive control. We found that thoracic aortas from both types of hypertensive rats had a greater sensitivity but diminished maximal developed tension in response to noradrenaline, when compared with that from normotensive rats. In superior mesenteric arteries, the sensitivity to noradrenaline was similar in all examined rat groups but in L-NAME-treated rats, these arteries exhibited decreased active force when stimulated with high noradrenaline concentrations, or with 100 mM KCl. These results indicate that hypertension leads to specific biomechanical alterations in diverse arterial types which are reflected in different modifications in their contractile properties.

Cardiovascular effects of high-fructose intake in rats with nitric oxide deficiency

ABSTRACT The aim of this study was to evaluate the involvement of nitric oxide (NO) system damage in the deleterious effects of high-fructose intake in rats. Fructose was administered as 10% solution in drinking water to twelve-week-old male Wistar rats for the period of 8 weeks. Blood pressure was measured by tail-cuff plethysmography. After sacrificing the rats at the end of the treatment, relative weights of heart and liver and biochemical parameters in blood plasma were determined. Reactivity of isolated conduit arteries was measured using a force-displacement transducer for recording isometric tension. Fructose drinking rats had increased blood pressure and impaired acetylcholine-induced relaxation of the thoracic aorta in comparison with control rats drinking just tap water. Relative liver weight and plasma concentrations of glucose and triglycerides were also elevated after fructose administration. In a further group of Wistar rats, inhibition of NO production by administration of NG-nitro-L-arginine methyl ester (L-NAME; 40 mg/kg/day) was performed throughout fructose intake. L-NAME treatment itself induces increase in blood pressure and relative heart weight as well as impairment in arterial relaxation and contractility. However, in these rats, fructose administration did not cause further elevation of blood pressure and other abnormalities observed in rats receiving fructose without L-NAME. Our results showed that in the state of NO deficiency (induced by L-NAME administration) fructose does not induce cardiovascular and metabolic alterations which develop in rats with a functional NO system. This indicates that impairment of the NO system may participate in many of the adverse effects induced by high-fructose intake.

Agmatine Modulation of Noradrenergic Neurotransmission in Isolated Rat Blood Vessels.

Agmatine, a vasoactive metabolite of L-arginine, is widely distributed in mammalian tissues including blood vessels. Agmatine binding to imidazoline and α₂-adrenoceptors induces a variety of physiological and pharmacological effects. We investigated the effect of agmatine on contractile responses of the rat pulmonary artery and portal vein induced by electrical stimulation of perivascular nerves and by exogenous adrenergic substances. Experiments were performed on isolated segments of rat main pulmonary artery and its extralobular branches, and portal vein suspended in organ bath containing modified Krebs bicarbonate solution and connected to a force-displacement transducer for isometric tension recording. Electrical field stimulation (EFS) produced tetrodotoxin-sensitive contractile responses of pulmonary artery and portal vein. Besides the well known vasorelaxant actions, we found that agmatine also produced a concentration-dependent inhibition of neurogenic contractions induced by EFS in pulmonary arteries; however, the agmatine treatment did not influence the responses to exogenous noradrenaline. The inhibitory effect on EFS-induced contractions was not abolished by the α₂-adrenoceptor antagonist rauwolscine. In portal vein, in contrast, agmatine increased spontaneous mechanical contractions and enhanced the contractions induced by EFS. The results suggest that agmatine can significantly influence vascular function of pulmonary arteries and portal veins by modulating sympathetically mediated vascular contractions by pre- and postsynaptic mechanisms.

PROTEIN REMODELING OF THE HEART VENTRICLES IN HEREDITARY HYPERTRIGLYCERIDEMIC RAT: EFFECT OF ACE-INHIBITION

The aim of this study was to determine whether protein remodeling of the heart ventricles and remodeling of the aorta were present in hereditary hypertriglyceridemic (hHTG) rats and whether treatment with the angiotensin-converting enzyme inhibitor, captopril could prevent these alterations. Three groups of rats were investigated in a four week experiment control Wistar /C/rats, hHTg rats, hHTg rats given captopril (100 mg/kg/day) (hHTg + CAP). In the hHTg group, the increased systolic blood pressure (SBP) was associated with hypertrophy of the LV and RV. Protein profile analysis revealed an enhancement of metabolic protein concentration in both ventricles. The concentration of total collagenous proteins was not changed in either ventricles. However, alterations in composition of cardiac collagen were detected, characterized by higher concentration of hydroxyproline in pepsin-insoluble fraction and lower concentration of hydroxyproline in pepsin soluble faction in the LV. Hypertrophy of aorta, associated with the reduction of nitric oxide dependent relaxation, was also present in hHTG rats. Captopril normalized SBP, reduced left ventricular hypertrophy (LVH), diminished metabolic protein concentration in both ventricles, and improved NO-dependent relaxation of the aorta. Furthermore, captopril partially reversed alterations in hydroxyproline concentration in soluble and insoluble collagenous fractions of the LV. We conclude that hypertrophy of both ventricles and the aorta are present in hHTG rats, along with protein remodeling of both ventricles. Captopril partially prevented left ventricular hypertrophy development and protein remodeling of the myocardium.