Emotional and sensory stress factors in myocardial pathology. Neurogenic and hormonal mechanisms in pathogenesis, therapy, and prevention

Experimental studies of psychophysiological factors in sudden cardiac death

Earlier research in the field of sudden cardiac death is reviewed. Such studies have largely oriented towards the provocation of myocardial injury and asystole in normal animals. However, such investigations constitute an inadequate model to describe the clinical appearance of sudden death, where underlying coronary disease is often present and the precipitating event is usually ventricular fibrillation rather than asystole. This report describes a series of studies designed to investigate the processes underlying cardiac vulnerability and the influence upon it of various psychological stresses. It is concluded that the primary mediator of ventricular vulnerability is the sympathetic nervous system. The efferent vagus appears to exert some protective influence against arrhythmias due to adrenergic stimulation. An appropriate clinical strategy for the treatment of malignant arrhythmias would therefore involve attempts to decrease cardiac sympathetic drive whilst at the same time enhancing vagal tone. Treatments are described which aim to bring this situation about by the use of clonidine, morphine sulphate, l-tryptophan and tyrosine. The use of neurochemical agents in this context appears promising.

Cardiovascular disorders associated with cocaine use: myths and truths

Cocaine produces a pattern of cardiovascular responses that are associated with apparent myocardial ischemia, arrhythmias, and other life-threatening complications in some individuals. Despite recent efforts to better understand the causes of cocaine-induced cardiovascular dysfunction, there remain a number of unanswered questions regarding the specific mechanisms by which cocaine elicits hemodynamic responses. This review will describe the actions of cocaine on the cardiovascular system and the evidence for the mechanisms by which cocaine elicits hemodynamic and pathologic responses in humans and animals. The emphasis will be on experimental data that provide the basis for our understanding of the mechanisms of cardiovascular toxicity associated with cocaine. More importantly, this review will identify several controversies regarding the causes of cocaine-induced cardiovascular toxicity that as yet are still debated. The evidence supporting these findings will be described. Finally, this review will outline the obvious deficits in our current concepts regarding the cardiovascular actions of cocaine in hope of encouraging additional studies on this grave problem in our society.

Changes in autonomic nervous activity during endoscopic retrograde cholangiopancreatography: a possible factor in cardiac complications

BACKGROUND AND AIMS

The changes of autonomic nervous activity during endoscopic retrograde cholangiopancreatography (ERCP) are closely related to the development of cardiovascular complications, such as arrhythmias and acute coronary syndrome. In the present study, the correlation between changes in hemodynamics and autonomic nervous activity during ERCP procedures was evaluated by analyzing heart rate variability and blood catecholamine levels.

METHODS

Twenty-three patients who underwent ERCP (ERCP group) and 15 control subjects who were only premedicated (C group) were studied. Ambulant ECG, blood pressure, arterial oxygen saturation, and blood level of catecholamine were measured. Autonomic nervous function was assessed by analyzing the spectral analysis and 1/f fluctuation. The low frequency power (LF power; 0.04-0.15 Hz), high frequency power (HF power; 0.15-0.40 Hz, indicator of parasymapathetic tone), the ratio of LF power to HF power (LF/HF ratio, indicator of sympathetic tone), and 1/f fluctuation (indicator of pleasant mood) were calculated.

RESULTS

Blood pressure and heart rate were increased and arterial oxygen saturation was decreased in the ERCP group during the endoscopic procedure. Changes in the parameters of autonomic nervous function (LF power, HF power, LF/HF ratio, and 1/f fluctuation) were significantly greater in the ERCP group than in the C group, especially during cholangiography. Moreover, blood levels of catecholamines were significantly increased during the ERCP procedure. In the C group, however, blood levels of catecholamines did not significantly change except directly after premedication.

CONCLUSIONS

Autonomic nervous activity varied greatly during cholangiography, demonstrating that ERCP has more than a little influence on the cardiovascular system. The results of the present study indicated that attention should be focused on changes in hemodynamics in patients with cardiovascular complications by monitoring the aforementioned hemodynamic parameters during ERCP.

Emotional stress and extracardiac regulation

It has been demonstrated in chronic experiments on animals (rabbits, rats) that in the presence of a predominance of sympathetic influences on the heart during emotional stress, the disturbances that appear in metabolism and myocardial ultrastructure promote a decrease in the electrical stability of the heart, the development of disturbances in cardiac rhythm, and arterial hypertension. A predominance of parasympathetic influences on the heart during stress, to the contrary, leads to an increase in the electrical stability of the heart, and also impedes an increase in the content of catecholamines and the development of structural injuries in the myocardium. At the same time, arterial hypertension is absent. An inference is drawn regarding the adaptive-trophic, protective action of the vagus nerves on the heart during emotional stress.

Changes in ganglion nodosum neurons associated with stress-related cardiac deficiency

Cell bodies of cardio-vascular receptors localized in the ganglion nodosum of rabbits exposed to experimental emotional stress were studied with the light and electron microscope and histochemically. Under emotional stress some rabbits demonstrated almost unchanged arterial pressure and only a small increase in heart rate, while other animals displayed strongly marked disturbances of their blood circulation leading to the acute heart deficiency at the end of the experiment. In the stress-resistant rabbits, microscopic anatomy and ultrastructure of neurons indicated their increased activity. Activities of lysosomal enzymes--acid phosphatase and aminopeptidase--were found to be at the control level, while the activity of mitochondrial enzyme--glutamate dehydrogenase--was slightly increased. On the other hand morphological evidence of severe hyperactivity and exhaustion was revealed in neurons of the stress-predisposed rabbits. Moreover the activities of all three enzymes studied were significantly increased. These results indicate correlation between the structural and metabolic changes occurring under experimental emotional stress in nodosal neurons and the extent of hemodynamic changes.

Mortality in affective disorder

472 bipolar patients were followed up retrospectively over 17 years. The patients that died were compared with the general population and a control group. The former comparison showed greater mortality from suicide, cardiovascular and respiratory causes in the index population and the latter, that the deceased were more likely to have been unmarried, with greater frequency and duration of admissions, a shorter follow-up period and were less likely to have received lithium treatment. The suicides were significantly younger at onset and death than the index and control groups, and suicide was uncommon where follow-up extended over 10 years.

Electrocardiographic changes in subarachnoid hemorrhage secondary to cerebral aneurysm. Report of 70 cases

Electrocardiographic (ECG) alterations in the course of sub-arachnoid hemorrhage (SAH) have frequently been reported. The most frequent anomalies reported were lengthening of the QT interval, very negative or positive deep T waves, elevation or depression of the ST segment and the presence of U waves. We report 70 cases of SAH secondary to rupture of intracranial aneurysm (part of a larger group of 150) with ECG changes. We review the literature with particular regard to discussion of the possible pathogenesis of ECG changes and to the way they may affect the general clinical course.

The dynamics of hypertension--an overview: present practices, new possibilities, and new approaches

Contemporary clinical evaluation of hypertensive patients must include observations encompassing the impact of environment, behavior, and sociologic factors on metabolism and physiology. As evidenced by animal and human studies, catecholamines are an important mediator between psychologic factors and cardiovascular physiology, but direct measurement of catecholamine levels has not proved useful. Measurement of hemodynamic variables--blood pressure, heart rate, and stroke volume--during standardized psychophysiologic challenges is advocated. With low-challenge standardized stressors that include alpha- and beta-adrenergic stimuli, inappropriate reactors can be classified according to whether blood pressure is elevated primarily by cardiac output, total systemic resistance, or a combination of both. Hypertensive patients can be similarly distinguished, and medication can then be custom-tailored to the underlying physiology. Extensive laboratory and clinical evidence points to significant interrelationships between the central nervous system and the cardiovascular system. Furthermore, cardiovascular physiologic and metabolic perturbances are distinctly different under conditions of mental vs physical stress. Most clinical testing assesses physical performance whereas the real-life challenges of today are primarily mental.

The physiological measurement of acute stress (public speaking) in bank employees

An evaluation of a number of non-invasive physiological measures of stress was conducted, using bank employees attending a two-week residential course. The stressor involved was the preparation and delivery of a 15-min public lecture. The physiological parameters measured were urinary excretion rates of noradrenaline (NA), adrenaline (A), dopamine and cortisol, the ratio of NA/A, salivary cortisol levels, heart rate and blood pressure. Measurements were taken at 08.30, 10.30, 12.30, 15.30 and 17.30 h on the day of the public lecture and on the following (control) day. The public lectures were given between 10.30 and 12.30 h. The urinary excretion rates of adrenaline and cortisol were significantly elevated immediately following, but not before, the public lectures. The ratio NA/A was significantly decreased and the salivary cortisol levels were significantly increased both immediately before and after the public lecture. Urinary excretion rates of noradrenaline and dopamine, blood pressure and heart rate were unchanged by the stressor. Measurement of salivary cortisol levels, as well as providing a simple, stress free, non-invasive collection procedure, more closely reflects in time the changes in plasma levels of the hormone, not suffering from the large lag-time involved with urinary hormone measurements. Salivary cortisol measurement would appear to be the measurement of choice in human stress studies where individual stress factors are to be identified and studied. The significance of the stress-induced elevation in cortisol and catecholamine levels in the link between illness and occupational stress is discussed.

Urinary cortisol excretion and mood ratings in aircraft cabin crew during a tour of duty involving a disruption in circadian rhythm

A psychophysiological study was carried out on 28 cabin crew, comprising two teams, who were to travel from Sydney to Los Angeles and return, with stopovers in Los Angeles of 58 and 82 hr respectively. Every urine sample for a period of nine days, commencing 2 days before the flight, was collected. The volume and time the sample was passed were recorded so that urinary cortisol secretion rates could be calculated. Mood was also rated on a scale scored 0-9 at the same time the urine sample was collected. A control group matched for age, sex ratio, and degree of manual labour involved in their occupation, but not involved with the flights, was included in the study for comparison. On the basis of urinary cortisol excretion rates, the crews in Sydney before the flight and in Los Angeles were more highly stressed than the control group. The urinary cortisol excretion rates were significantly greater than those of the control group in Sydney before the flight, in Los Angeles, and during the return flight, but not on the flight out. The high excretion rates before the flight were attributed to an apprehension factor, whereas the elevated values in Los Angeles and during the flight back were attributed to a disruption in circadian rhythm. A factor analysis of mood ratings showed three major factors assessing vitality, distress, and relaxation. Analysis of variance of the mood ratings showed significant changes over the tour of duty for 13 of the 14 moods.

Subcellular bases of cardiac disturbance in experimental informational neurosis

In experimental informational neurosis, accompanied by the development of stable arterial hypertension, tachycardia and dystrophic alterations in myocardium, the contractile protein ability to generate force and produce work as well as the power of the contractile process are significantly decreased and so is the intensity of Ca2+ transport through membranes of sarcoplasmic reticulum and mitochondria. Ca2+ content in these structures and energetic supply to the cardiac muscle do not change as compared with the control. Noradrenaline content in myocardium increases 5-fold compared with the control and 2.5-fold compared with the norm, while blood content falls to zero (sympathetic neuro-muscular contact is 'locked up' for noradrenaline outflow into the blood); dopamine content increases. Adenylate cyclase sensitivity to the stimulating effect of noradrenaline and NaF diminishes. Basal activity of phosphodiesterase increases, and its sensitivity to the inhibitory action of high calcium concentrations decreases. The disturbance in these systems may, on the one hand, be due to neural effects, and pressure overload of the heart, on the other hand, to the sharp rise in noradrenaline content in the myocardium and the change in the activity of cyclic adenosine monophosphate enzymes. It is suggested that similar changes may take place in the human myocardium and may underlie the cardiac weakness.

Attenuation of stress-induced hypertension by exercise independent of training effects: an animal model

The present study attempted to determine if exercise, in the absence of physical training, could alter development of hypertension during chronic exposure to a psychosocial stressor. Two groups of genetically normotensive rats were exposed to social stress for 7 days, following 5 weeks of acclimation to social isolation. One group had access to exercise in a running wheel during the stress period, while the second group did not. Blood pressure, heart rate, body weight, and running activity were monitored throughout the study, and heart and adrenal gland weights were obtained following sacrifice of the animals after exposure to stress. Blood pressure increased significantly to hypertensive levels on days 4 and 7 in the group denied access to exercise but was unchanged in the exercise group. Degree of attenuation of stress-induced hypertension was unrelated to amount of running activity. There were no differences in body weight, heart rate, or organ weight between groups. Exercise appeared to act specifically via diversional, or coping, mechanisms to buffer the response of the body to stress.

Cardiac copper, magnesium, and zinc in recent and old myocardial infarction

X-ray fluorescence spectrometry and atomic absorption spectrometry were used in a quantitative study of zinc, copper, and magnesium in 71 postmortal human hearts. Samples were obtained from individuals who had demonstrated no previous clinical or subsequent pathological findings of myocardial infarction and from victims of a recent or an old infarction. A significant difference (p<0.001) in the elemental levels was observed between the noninfarct and the recent infarct groups. The noninfarct group had higher cardiac levels of all three elements. However, the difference in elemental concentrations between the noninfarct and the old-infarct groups was not significant. Cardiac levels of zinc (p<0.001) and copper (p<0.01) were significantly greater in the old-infarct group than in the recent-infarct group. Magnesium levels were higher in the recent-and-old-infarct group than in the recent infarct group (p<0.01). It is possible that the elements are redistributed during myocardial infarction, and that uptake of these elements (from the serum pool) by the heart may be important in maintaining myocardial integrity and function.

Life changes and urinary norepinephrine in myocardial infarction

The relationship between norepinephrine and stress caused by life changes was assessed using urinary norepinephrine levels and responses to a 57-item stress questionnaire interview obtained from 21 post-myocardial infarction and 27 healthy control male and female subjects. High correlations between norepinephrine and duration of present stress and duration and severity of life changes, and moderate correlations between norepinephrine and anxiety and depression were found among the post-infarction group. No significant correlations were found in the control group. Post-infarction subjects with elevated norepinephrine had significantly higher scores on duration of present stress and duration and severity of life changes than did post-infarction subjects with normal norepinephrine levels. Control subjects with normal and elevated norepinephrine did not differ significantly on any of the comparison variables. Standard risk factors failed to add significantly to the prediction of norepinephrine in either group. However, 68.3 percent of the variance in norepinephrine was accounted for by a single predictor, the duration of present stress.

Effects of sulfinpyrazone on ventricular vulnerability in the normal and the ischemic heart

The effects of sulfinpyrazone were studied in 33 chloralose-anesthetized dogs. Ventricular fibrillation thresholds, mid diastolic thresholds and duration of the effective refractory period were determined in the normal heart after intravenous administration of sulfinpyrazone, 30 mg/kg body weight. The drug significantly raised the ventricular fibrillation threshold by 24 percent and the mid diastolic threshold by 36 percent and prolonged the effective refractory period by seven percent. The influence of sulfinpyrazone during acute myocardial ischemia was evaluated before and during a 10 minute occlusion of the left anterior descending coronary artery and after abrupt release of the occlusion. Although the drug afforded significant protection during coronary occlusion, it had no effect on the ventricular fibrillation threshold after reperfusion. Because potent cardiocardiac reflexes are elicited during ischemia, the influence of sulfinpyrazone on the ventricular fibrillation threshold was studied during norepinephrine infusion. Sulfinpyrazone attenuated the reduction of the ventricular fibrillation threshold during sympathetic humoral stimulation. Its effect was additive to beta adrenergic blockade with practolol and membrane stabilization with lidocaine. This investigation suggests that sulfinpyrazone exerts significant effects on ventricular vulnerability of both the normal and the ischemic myocardium. Further studies are needed to elucidate its precise mechanism of action.

Influences of hypothermia, cold, and isolation stress on the severity of coronary artery ligation-induced arrhythmias in rats

With a view to increasing the severity of the arrhythmias that arise following coronary artery ligation in anesthetized rats, the influences of exposure to lowered environmental temperature (LET) (21 to 13 degrees C) and isolation stress were examined. Housing rats singly for 48 hr, prior to the induction of arrhythmias, caused the most marked changes in the severity of the model; the incidence of ventricular fibrillation and mortality were increase from 43 to 90% and 9 to 60%, respectively. Exposure of multiply housed rats to LET for 48 hr also significantly increased mortality from fibrillation. A combination of LET plus isolation stress, however, did not further increase the severity of the arrhythmias following ligation. Acute hypothermia (body temperature reduced to 30 or 25 degrees C) did not significantly enhance the severity of the model.

Psychosocial and behavioral influences in the pathogenesis of acquired cardiovascular disease

When taken together, studies relating psychosocial and behavioral factors to cardiovascular disease phenomena provide justification for the conclusion that such factors are importantly involved. We would emphasize the need to study and evaluate the interaction of environmental and biological factors in both laboratory studies of pathogenesis as well as in clinical studies of management. Indeed, upon careful scrutiny, even the accepted "nonbehavioral" risk factors such as hypercholesterolemia, hypertension, cigarette smoking, obesity, and sedentary lifestyles are each composite manifestations rather than single pathogens whose identities are powerfully impregnanted and bolstered by varieties of behavioral and psychosocial underpinnings. In view of the awesome impact of contemporary cardiovascular disease, both in terms of its increasing socioeconomic importance and its biologic devastation, we can not long afford comprehensive public health programs without increased and improved attention to psychosocial and behavioral influences in the pathogenesis of acquired cardiovascular disease.

Effects of denial on mood, compliance, and quality of functioning after cardiovascular rehabilitation

The effect of denial upon mood, perceived quality of functioning and compliance with medical advice was studied in 45 coronary patients three months after completing an intensive cardiovascular rehabilitation program. Deniers reported less mood disturbance before and after the program and at three-month follow-up compared with nondeniers. Denial was inversely related to Total Mood Disturbance at all three evaluations. Both groups showed a decline in mood disturbance with treatment and loss of improvement at follow-up. The degree of change was significantly greater for nondeniers. There was no significant difference between groups in any area of compliance or perceived quality of functioning. Denial showed no relationship to overall compliance or quality scores. Total Mood Disturbance was inversely related to both compliance and perceived quality of functioning and appears to be a majro determinant of rehabilitation outcome.

Role of alpha- and beta-adrenergic activation in ventricular fibrillation death of corticoid-pretreated rats

Death in ventricular fibrillation was induced consistently in desoxycorticosterone acetate-pretreated rats by the beta-adrenergic agonist isoproterenol but not by norepinephrine or epinephrine, both of which possess alpha- as well as beta-adrenergic activity. Aminophylline, which enhances beta-adrenergic activity, and phenoxybenzamine, an alpha-receptor blocking agent, were used to study the roles of alpha- and beta-adrenergic stimulation in the production of ventricular fibrillation. With the addition of aminophylline, both norepinephrine and epinephrine produced death in ventricular fibrillation, and the existing cardiotoxicity of isoproterenol was potentiated. Similarly, in the presence of phenoxylbenzamine, doses of norepinephrine and epinephrine that had been well tolerated became lethal. Internventions that favor beta-adrenergic preponderance, either by enhancing beta-effects or by blocking protective alpha-adrenergic activation, apparently increase the arrhythmogenic propensity of norepinephrine and epinephrine in steroid-pretreated rats. The similarity of some forms of stress to the experimental protocol of chronic steroid treatment followed by acute catecholamine exposure is discussed.

Corticosteroid involvement in the changes in noradrenergic responsiveness of tissues from rats made hypertensive by short-term isolation

1 The responses to noradrenaline and to noradrenergic nerve stimulation of spontaneously beating right atria, electrically driven left atria and vasa deferentia taken from rats made hypertensive by short-term isolation have been compared with the responses of tissues from normotensive, group-housed animals.2 Adrenocortical activity of isolated animals was assessed by plasma corticosterone determinations and measurement of adrenal weights.3 The hearts of the isolated animals were weighed and the myocardial contents of water, sodium, potassium and calcium were measured.4 Spontaneously beating right atria from isolated animals showed a lower resting rate, no difference in the response to nerve stimulation but a greater sensitivity to noradrenaline compared to atria from group-housed animals.5 Vasa deferentia from isolated animals showed a decreased maximal response to noradrenaline, but no change in noradrenaline sensitivity or in the response to transmural stimulation.6 There were indications of hyperactivity of the adrenals throughout a 5 week period of isolation, manifest as elevated plasma corticosteroid levels and increased adrenal weights.7 Myocardial levels of sodium and calcium were elevated at the same time as the tissue level of potassium was reduced, but heart weights did not significantly change.8 It is possible that adrenal steroid action caused the changes in tissue ionic balance. These ionic disturbances may have been responsible for some of the changes in tissue sensitivity found in the isolated hypertensive animals.

Neural and psychologic mechanisms and the problem of sudden cardiac death

Brain stimulation can provoke a variety of arrhythmias and lower the ventricular vulnerable threshold. In the animal with acute myocardial ischemia such stimuli suffice to provoke ventricular fibrillation. Vagal neural traffic or adrenal catecholamines are not the conduits for this brain-heart linkage. Accompanying increases in heart rate or blood pressure are not prerequisites for the changes in cardiac excitability. Increased sympathetic activity, whether induced by neural or neurohumoral action, predisposes the heart to ventricular fibrillation. Protection can be achieved with surgical and pharmacologic denervation or reflex reduction in sympathetic tone. With acute myocardial ischemia, augmented sympathetic activity accounts for the early surge of ectopic activity frequently precipitating ventricular fibrillation. Asymmetries in sympathetic neural discharge may also contribute to the genesis of serious arrhythmias. The vagus nerve, through its muscarinic action, exerts an indirect effect on cardiac vulnerability, the consequence of annulment of concomitant adrenergic influence, rather than of any direct cholinergic action on the ventricles. There exist anatomic, physiologic as well as molecular bases for such interactions. Available experimental evidence indicates that environmental stresses of diverse types can injure the heart, lower the threshold of cardiac vulnerability to ventricular fibrillation and, in the animal with coronary occlusion, provoke potentially malignant ventricular arrhythmias. Available evidence indicates that in man, as in the experimental animal, administration of catecholamines can induce ventricular arrhythmia, whereas vagal activity exerts an opposite effect. Furthermore, in certain subjects diverse stresses and various psychologic states provoke ventricular ectopic activity.

Changes in the coronary vascular system following prolonged exposure to stress

Hearts of stressed rats showed marked changes in the coronary vasculature. It was suggested that such morphological changes could be explained on the basis of an increased coronary vascular permeability. Endogenous inflammatory substances could induce swelling of the endothelial cells and cause separation of the neighbouring cells from one another, thus allowing the passage of lipid molecules through the endothelial lining. In order to gain supportive evidence for the above hypotheses an electron microscope study was undertaken. The presence of junctional gaps in the endothelial lining of the coronary vascular system was observed following prolonged stress, as well as platelet aggregation. The use of lipid staining of frozen sections indicated the presence of large lipid deposits in the arteriole walls, corresponding to vacuoles seen previously. It would appear therefore, that prolonged exposure to stress may result in pathological changes in the myocardium associated with changes in the vascular endothelial permeability, and platelet aggregation. Pathological changes induced in this way, however, should be inhibitd by high glucocorticoid levels and should not be manifested until adaptation of the steroid response to stress has occurred. Measurement of plasma glucocorticoid levels over the period of prolonged stress shows a good correlation between the adaptation of the steroid response and the onset of a progressive degeneration of the coronary vascular system.

Behavioural epidemiology and coronary heart disease: some sources of error and an alternative conceptual model

While the quantity of evidence relating behaviour and coronary heart disease is great, the quality is variable. It is possible to discern two broad categories of research error, the methodological and the conceptual, to account for this. The former may be corrected by sufficiently careful study design: the latter may require a complete re-examination of hypotheses. An alternative conceptual model is proposed in which three components (a) a surfeit of adversity in the absence of support, (b) consequent arousal and activation of the cardiovascular system, and (c) the coexistence of one or more of a well documented set of organic risk factors, allow the integrated and systematic testing of hypotheses relating behaviour and coronary heart disease. The authors are presently employing this conceptual model in the investigation of a number of such hypotheses.

Correlations of normality and nervousness with cardiovascular functions in pointer dogs

Methylphenidate, 0.5 mg/kg, injected intravenously, was used in 10 normal (A line) and 10 genetically nervous (E line) dogs in a blind-design experiments to aid in prediction, from cardiovascular recordings alone, of behavioral normality versus nervousness. The prediction was 75% correct, based on heart rate (HR), form of the electrocardiogram (EKG), pattern of sinus arrhythmia, and pattern of HR response to methylphenidate. Nervous dogs were found to have slower baseline HR's, delayed return of HR to baseline after methylphenidate, greater occurrence of baseline EKG abnormalities and much greater frequency of these after methylphenidate. Degree of nervousness was found to correlate rather highly (1) negatively with baseline HR level, (2) negatively with speed of BP response, and (3) positively with frequency of some of the EKG manifestations. These data, indicative of a relative inertness of physiological functions of nervous pointer dogs compared with normal pointers, are consistent with the behavioral and some of the biochemical findings previously reported.

Myocardial sensitivity to catecholamines following exposure of rats to irregular, signalled footshock

Emotional stress is associated with an increased activity of both the pituitary-adrenal cortical system and the sympathetic-adrenal medullary systems resulting in raised plasma levels of glucocorticoids and catecholamines. There is evidence to suggest that prolonged stress induced adrenergic hyperactivity initiated myocardial pathogenesis and that this may relate to a corticosteroid catecholamine interaction. In the present study driven atrial strips removed from stressed male CSF rats were found to exhibit an enhanced sensitivity to both norepinephrine and epinephrine. These animals had previously been subjected to irregular foot shock associated with a warning signal; a situation producing a high plasma steroid level. The enhanced myocardial sensitivity to both catecholamines was observed in naive animals subjected to a single period, and persisted unchanged in animals stressed daily over a 28 day period. The hypersensitivity of the myocardium observed immediately after stress was maintained for at least 24 hr, whereas the circulating steroid level had returned to control values within 3 hr. In animals subjected to regular stress without a warning signal, a situation producing a much lower steroid level, no enhanced myocardial sensitivity was observed. While the aetiology of the phenomenon of enhanced myocardial sensitivity to catecholamines is not entirely understood, the evidence presented suggests that it may be related to the extreme elevation of circulating glucocorticoids. The sensitivity of the vas deferens however, was unaltered even though the animals were subjected to the stressor producing a high plasma steroid level. This apparent specifcity of the stress induced sensitivity change is discussed on the basis of receptor differences.

Morphological changes induced in rats following prolonged exposure to stress

Prolonged exposure of male C. S. F. rats to irregular signalled footshick from which they could escape for up to 71 days produced profound morphological changes. Retardation in growth, adrenal hypertrophy associated with an increase in the zona fasiculata a-nd zona reticularis, and changes in the microcirculation of the heart were observed. There was a significant degree of congestion and dilatation of the microcirculation which was most marked in large venules, collecting venules and veins. An increase in PAS +ve material marginated in the venous endothelium was observed also, together with a suggested increase in mast cells and presence of vacuoles in the intima-media of the coronary arterioles. No pathological changes were observed in the renal cortex and medulla or the gastric lining. The changes in the microcirculation of the heart are discussed in terms of an oedematous reaction and a histamine type leakage of the endothelial lining.

Autonomic manifestations of tetanus

Two patients with tetanus are reported to illustrate the involvement of the sympathetic and parasympathetic nervous system respectively. Aspects of the autonomic manifestations of tetanus are illustrated and discussed.

Hypotension in tetanus

Three patients with severe tetanus had episodes of profound arterial hypotension lasting from minutes to hours. The blood pressure was recorded continuously for 13, 19, and six days respectively by an intra-arterial catheter, and other measurements included heart rate, central venous pressure, cardiac output, and blood gases.The hypotension was distinguished from that of "shock", for there was no clinical evidence of peripheral vasoconstriction and no tachycardia. It could not be attributed to disturbances of salt and water balance. During episodes of hypotension the blood pressure fell as low as 32/16 mm Hg, the heart rate fell from a mild tachycardia to normal values or a mild bradycardia, and the central venous pressure did not rise. The onset and the end of such episodes was often abrupt and the hypotension was often produced in response to a stimulus. In one patient extreme hypotension followed the aspiration of secretions from the trachea. These changes may represent another effect of tetanus on autonomic nervous activity, including impairment of baroreceptor reflexes.

Metabolic response during impending myocardial infarction. II. Clinical implications

The immediate local metabolic response of the myocardium to acute regional ischemia is determined by an interaction of various influences. These include: (1) the extent of and the variability in reduction of blood flow; (2) the degree and persistence of hypoxia; and (3) the effects of local release of catecholamines, particularly in relation to loss of intracellular potassium.

The subsequent metabolic response of the myocardium is partly dependent on the degree of impairment locally of normal myocardial metabolism and partly on the systemic reaction to increased catecholamine activity and hence on: (1) adipose tissue lipolysis; (2) hepatic and muscle glycogenolysis; (3) insulin suppression; and (4) growth hormone and cortisol activity. These determine the extent of the uptake from blood of FFA and glucose by the ischemic myocardium.

There is increasing evidence that high arterial concentrations of FFA can depress myocardial performance by leading to ventricular arrhythmias and decreased contractility. This effect probably depends on a critical interaction between the local concentration of FFA, catecholamines, and hypoxia.

Metabolic intervention in the management of heart attacks should accordingly be directed toward reducing mobilization of adipose tissue FFA and increasing myocardial glycolytic activity.