The question was addressed whether short-term (4 hour) NO deficiency, inducing an increase in blood pressure in anaesthetized dogs, does influence proteosynthesis in the myocardium and coronary arteries. A potentially positive answer was to be followed by the study of the supporting role of ornithine decarboxylase for the polyamines pathway. NG-nitro-L-arginine-methyl ester (L-NAME) (50 mg/kg per hour) was administered i.v. to inhibit NO synthase. After the first L-NAME dose diastolic blood pressure increased from 131.8 ±2.0 to 149.4 ±3.9 mm Hg (p< 0.001) and was maintained at about this level till the end of the experiment. Systolic blood pressure only increased after the first dose (from 150.8 ±1.1 to 175.0 ±5.8 mm Hg, p<0.01), returning thereafter to the control level. Similarly, the heart rate declined only after the first dose (from 190.4±5.3 to 147.6±4.5 beats/min, p<0.01). Total RNA concentrations increased in the left cardiac ventricle (LV), the left anterior descending coronary artery (LADCA) and left circumflex coronary artery (LCCA) by 15.9 ±0.7, 29.7 ±1.3 and 17.6 ±1.0%, p<0.05, respectively. The same applied to [14C]leucine incorporation (by 86.5 ±5.0, 33.5 ±2.6, 29.3±4.1 %, p<0.05, respectively). The above parameters indicated an increase of proteosynthesis in the LV myocardium and both coronary arteries LADCA and LCCA after short-term NO deficiency. Surprisingly, the ornithine decarboxylase activity in the LV myocardium decreased significantly by 40.2± 1.6 % (p<0.01) but the changes were not significant in the coronary arteries. This unexpected finding makes the role of polyamines in increasing proteosynthesis during a pressure overload due to NO deficiency questionable.
The metabolites of arginine were recently shown to be involved in cardiovascular control. The study addresses the general cardiovascular response of anaesthetized rats to agmatine, a decarboxylated arginine. The relation between two arginine metabolic pathways governed by arginine decarboxylase and nitric oxide synthase was investigated. Intravenous administration of agmatine 30 and 60 μM/0.1 ml saline elicited remarkable hypotension of 42.6±4.6 and 70.9±6.5 mm Hg, respectively. The hypotension was characterized by long duration with half-time of return 171.6±2.9 and 229.2±3.8 s, respectively. The time of total blood pressure (BP) recovery was about 10 min. Dose-dependent relaxation to agmatine was also found in aorta rings in vitro. Both doses of agmatine administered 60-180 min after NO synthase inhibition (L-NAME 40 mg/kg i.v.) caused greater hypotension 59.0±7.6 and 95.8±8.8 mm Hg (P<0.01 both) compared to animals with intact NO synthase, but this was accompanied by a significant shortening of the half-time of BP return. If agmatine was administered to hypertensive NO-deficient rats (treated with 40 mg/kg/day L-NAME for 4 weeks), similar significant enhancement of hypotension was observed at both agmatine doses, again with a significant shortening of half-time of BP return. It can be summarized that the long-lasting hypotension elicited by agmatine was amplified after acute or chronic NO synthase inhibition, indicating a feedback relation between the two metabolic pathways of arginine.
Data concerning the effect of NO on the function and structure of the heart are controversiaL We have studied two main questions: (i) Does the heart muscle reflect the hypertension induced by long-term inhibition of NO synthase? (ii) Since the arginine-NO pathway is also operative in the autonomic nervous system, the second goal was to ascertain the possible changes of the adrenergic nervous system in the heart after long-term NO synthase inhibition. Wistar rats were administered L-NAME in drinking water (50 mg/kg bw/day) for 8 weeks. Systolic blood pressure and heart rate were monitored weekly. The heart/body weight ratio were determined at the end of experiment The adrenergic nerve terminals visualized by histochemistry were counted according to Haug’s point counting method. Blood pressure increased significantly in L-NAME-treated rats. No changes were found in the heart rate. Heart/body weight ratio increased markedly. Surprisingly, the density of adrenergic nerve terminals did not alter accordingly. The density of adrenergic nerve terminals in the left ventricle and septum decreased but no significant changes were found in the left atrium and the right ventricle. Hypertension due to NO deficiency induced cardiac hypertrophy that was characterized by a decline in the density of adrenergic innervation of the overloaded left ventricle and septum.
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.
Morphometry of cardiomyocytes and capillary domains in the left ventricle myocardium was performed in control rats and in rats treated with nitro-L-arginine methyl ester 50 mg/kg/day p.o. for a period of 8 weeks. The myocardial hypertrophy accompanying the NO-deficient hypertension induced by chronic inhibition of NO synthase is characterized by an increase in thickness of myocardial fibres and by relative rarefaction of the capillary bed, e.g. an alteration in myocardial structure which is typical for pressure overload hypertrophy.
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.
Coronary and carotid artery structure was studied in rats in order to analyze the processes in the cardiovascular system in NO-deficient hypertension model. Long-term inhibition of NO synthase was induced by L-nitro arginine methyl ester (L-NAME, 50 mg/kg/day p.o.) for a period of 8 weeks. An increase in blood pressure and heart/body weight ratio confirmed the reliability of the model. The wall thickness as well as the calculated wall area of the coronary artery increased by 70 % and 50 %, respectively, in comparison to control vessels. The wall thickness and the calculated wall area of the carotid artery increased by 73 % and 70 %, respectively. Further analysis indicated that both the tunica intima and tunica media in the coronary and the carotid artery increased quantitatively in a similar manner. Remarkable differences were found in the contribution of cellular and noncellular components in the tunica media of the coronary and carotid arteries of experimental animals. The calculated extracellular area increased by 116 % in comparison to the control coronary artery and by 97 % in comparison to the control carotid artery. The increase in extracellular matrix of the tunica media of coronary and carotid arteries seems to be basic cause of the remodelling of the vessels studied.
This review compares the geometry of conduit coronary arteries in man and animals, namely the wall/diameter ratio (1:7.4 and 1:15 respectively). The left and right ventricle volume determines the geometry (segment length and diameter) of both branches of the left coronary artery: ramus interventricularis anterior and ramus circumflexus; the range of deformation of the latter was substantially smaller. The heterogeneity of deformation was also found along the ramus interventricularis anterior, the deformation decreasing towards the apex. The above relations have consequences (i) on the haemodynamics (passive changes in conduit segment resistance), (ii) the deformation of coronary arteries triggers metabolic processes in the coronary wall. Four hours' lasting cardiac volume or pressure overload brought about an increase in the RNA content not only in the myocardium, but also in the coronary artery. The process is reversible. Moreover, the range of the RNA increase is in full concert with the heterogeneous deformability of the respective segment of the coronary tree.