Noradrenaline-induced myocardial infarction in monkeys given an atherogenic diet

Mechanism of catecholamine-induced proliferation of vascular smooth muscle cells

BACKGROUND

Catecholamines have been shown to aggravate atherosclerosis in animals and humans, and abnormal proliferation of vascular smooth muscle cells (VSMC) is a key event in the early stage of atherosclerosis. Catecholamines may be involved in such cell growth. Therefore, a series of experiments using cultured VSMC was performed to elucidate their possible mitogenic effect.

METHODS AND RESULTS

We examined the mitogenic effect of catecholamines using rat aortic smooth muscle cells (VSMC) by measuring [3H]thymidine incorporation, checking with flow cytometry, and counting the cell number directly. Furthermore, the catecholamine-activated signal transduction pathway was assessed by measurement of the formation of inositol 1, 4, 5-triphosphate, intracellular Ca2+ concentration, mitogen-activated protein kinase (MAPK) activity, and mitogenic gene expression. Norepinephrine (NE) and phenylephrine stimulated [3H]thymidine incorporation and cell growth. Clonidine and isoproterenol showed little of such effects. Prazosin was more effective than either yohimbine or propranolol in suppressing the mitogenic effect of NE, indicating that catecholamine-induced VSMC proliferation is mediated by alpha 1-adrenoceptors. The alpha 1-adrenoceptor activation was coupled to pertussis toxin-insensitive Gq-protein and triggered phosphoinositide hydrolysis with subsequent activation of protein kinase C and MAPK in VSMC. In response to NE, both 42- and 44-kD MAPK were activated and tyrosine was phosphorylated. alpha 1-Adrenoceptor stimulation with NE also caused accumulation of c-fos, c-jun, and c-myc mRNA. Chloroethylclonidine completely blocked the alpha 1-adrenoceptor-mediated mitogenesis.

CONCLUSIONS

The effect of catecholamines appears to be mediated via the activation of the chloroethylclonidine-sensitive alpha 1-adrenoceptors that triggers the phosphoinositide hydrolysis and activates the MAPK pathway, leading to DNA synthesis and cell proliferation.

Adrenaline and noradrenaline as possible chemical mediators in the pathogenesis of arteriosclerosis

We studied the relationships between adrenaline and noradrenaline and factors associated with arteriosclerosis to determine whether catecholamines contribute to the atherogenetic process. We investigated the effects of adrenaline and noradrenaline on cultures of vessel wall cells from rats and analyzed plasma catecholamine levels in humans exposed to atherogenic risk factors, undergoing hemodialysis treatment or following myocardial infarction or stroke. I. Cultured endothelial and smooth muscle cells from vessel walls exhibited enhanced proliferation when exposed to adrenaline or noradrenaline. This indicates that catecholamines trigger the activation of vascular wall cells in vitro. Such activation, the unspecific mesenchymal reaction, is the predominant characteristic change in early atherogenesis. II. In individuals subjected to the atherogenic risk factors smoking, essential hypertension and mental stress, plasma adrenaline concentrations were statistically significantly elevated. Mental stress also caused significantly elevated plasma noradrenaline levels. Plasma noradrenaline concentrations were also elevated in smoking and hypertensive individuals when compared with certain controls, but the differences failed to be statistically significant. III. In dialysis patients, plasma adrenaline and noradrenaline concentrations showed a positive correlation with the activity of the sclerotic process; i.e., plasma catecholamine concentrations increased with the severity of the disease. IV. Patients with persisting arteriosclerotic vascular disease, i.e., patients who had had a myocardial infarction or stroke, had significantly elevated plasma adrenaline and/or noradrenaline levels as late as one year after the event. The results of our investigations suggest that adrenaline and noradrenaline may act as chemical mediators during atherogenesis in man, thus contributing to the development and subsequent complications of arteriosclerosis.

A possible role of catecholamines in atherogenesis and subsequent complications of atherosclerosis

Cultured smooth muscle cells (SMC) from rat aorta and endothelial cells (EC) from pig aorta were used to study the effect of the catecholamines epinephrine and norepinephrine on cell proliferation. Both stimulated growth of SMC and EC when added to the culture medium. Besides epinephrine and norepinephrine, dopamine and some of their metabolites also stimulated proliferation of cultured endothelial cells. Smooth muscle cells originating from rats being exposed to atherosclerotic risk factors, like diabetes, hypertension and balloon-injury, exhibited an increased susceptibility to these catecholamines compared to SMC from control animals. In comparison to normotensive control animals a 10-fold elevated plasma concentration of epinephrine was found in hypertensive rats. In man plasma epinephrine and norepinephrine concentration was determined in a healthy control group and in patients suffering from diabetes mellitus and coronary artery disease. Plasma epinephrine and norepinephrine levels were similar in patients suffering from diabetes mellitus compared to the control group. But in patients with coronary artery disease significantly higher plasma concentrations for epinephrine (p less than 0.001) and norepinephrine (p less than 0.01) were observed. These data support the hypothesis that catecholamines may play a role in the development and subsequent complications of atherosclerosis.

Catecholamine-induced aggravation of aortic and coronary atherosclerosis in monkeys

Advanced aortic and coronary atherosclerosis was produced in rhesus monkeys by means of two procedures' (a) high fat and cholesterol feeding for 7 months, and (b) this diet coupled with daily i.v. injection of adrenaline (50 micrograms/kg body weight). A total of 83% of the monkeys subjected to procedure (b) developed markedly advanced atherosclerosis in the form of fibrous plaques in the aorta and coronary artery, while these lesions were much less frequent in the other group. The ratio of total to free serum cholesterol, significantly increased and the aortic cholesterol content was very high in monkeys subjected to both the atherogenic diet and adrenaline injections. It is suggested that catecholamines cause vascular injury and, in the presence of hyperlipidaemia, cause accelerated and aggravated atherosclerosis.

Serum lipid profiles in patients of myocardial infarction in the Chandigarh area (Northern India)

To study the incidence of hyperlipoproteinaemia in patients with myocardial infarction (MI) in the Chandigarh area, estimations of various lipids have been carried out in 83 patients. A serial study has been carried out in 31 patients. Serum lipoproteins and uric acid were also estimated. Results show an incidence of only 18% hypercholesterolaemia in patients with MI and 15% in normal subjects. Age-wise distribution of hypercholesterolaemia was slightly higher in 41-60 years old patients when compared with other age groups. No other abnormality in lipid profile was observed. Hyperuricaemia was not observed. These results, therefore, differ markedly from those of similar studies published from the western world.

Systemic stress in the production of cardiac thrombosis in hypercholesterolaemic rats

An experimental study to elucidate the effects of feeding a high fat diet, hypercholesterolaemia and superadded acute and chronic stress on the production of cardiac thrombosis was carried out in rats. The high fat diet contained 25 percent butter rat providing 45 percent calories from fat which produced significant increase of serum cholesterol and other lipids. Acute stress was induced by two injections of adrenaline on a single day which caused a marked transient alteration of haemodynamics. Chronic stress was of two types, physical and metabolic. The physical stress was induced by repeated exposure of the rats to electric shock or roller drum exercise, while metabolic stress was caused by repeated injection of ACTH. Rats of both acute and chronic stress groups showed variable degree of medial degeneration, hyaline and fibrinoid intimal deposits and calcification in coronary arteries. Cardiac thrombi were seen in 30 percent animals subjected to adrenaline shock. Among the chronic stress procedure 17 percent rats exposed to electric shock and only one rat of the ACTH group developed cardiac thrombosis but no thrombus was detected in those exposed to roller drum exercise. The myocardium showed patchy necrosis with or without calcification, Spontaneous mortality was maximum following acute adrenaline shock (25 %) while electric shock caused mortality in 17 percent animals. The other procedures did not lead to spontaneous mortality. This study highlights the significant role of high fat intake, hypercholesterolaemia and systemic stress in the pathogenesis of acute cardiac thrombosis and myocardial necrosis/infarction.