Urinary excretion of catecholamines and their main metabolites after myocardial infarction; relationahip to the clinical syndrome

Biochemical Assessment of Pheochromocytoma and Paraganglioma

Pheochromocytoma and paraganglioma (PPGL) require prompt consideration and efficient diagnosis and treatment to minimize associated morbidity and mortality. Once considered, appropriate biochemical testing is key to diagnosis. Advances in understanding catecholamine metabolism have clarified why measurements of the O-methylated catecholamine metabolites rather than the catecholamines themselves are important for effective diagnosis. These metabolites, normetanephrine and metanephrine, produced respectively from norepinephrine and epinephrine, can be measured in plasma or urine, with choice according to available methods or presentation of patients. For patients with signs and symptoms of catecholamine excess, either test will invariably establish the diagnosis, whereas the plasma test provides higher sensitivity than urinary metanephrines for patients screened due to an incidentaloma or genetic predisposition, particularly for small tumors or in patients with an asymptomatic presentation. Additional measurements of plasma methoxytyramine can be important for some tumors, such as paragangliomas, and for surveillance of patients at risk of metastatic disease. Avoidance of false-positive test results is best achieved by plasma measurements with appropriate reference intervals and preanalytical precautions, including sampling blood in the fully supine position. Follow-up of positive results, including optimization of preanalytics for repeat tests or whether to proceed directly to anatomic imaging or confirmatory clonidine tests, depends on the test results, which can also suggest likely size, adrenal vs extra-adrenal location, underlying biology, or even metastatic involvement of a suspected tumor. Modern biochemical testing now makes diagnosis of PPGL relatively simple. Integration of artificial intelligence into the process should make it possible to fine-tune these advances.

The clinical utility of plasma and urine metanephrines in hypertensive emergency

INTRODUCTION

Metanephrines (MTNs) are metabolites of catecholamines and are constantly produced in high amounts by pheochromocytomas and paragangliomas (PPGLs). Marked MTN elevations (> 3 times the upper limit of normal [ULN]) are highly suggestive of PPGL. The frequency of marked MTN elevations in non-PPGL hypertensive emergencies (HTNEs) is unknown.

METHODS

We retrospectively analyzed plasma free metanephrine (PMTN) and 24-h urinary fractionated metanephrine (UMTN) levels in 48 consecutive patients (59.7 ± 15.6 years; 48% female; BMI: 31 ± 9.7 kg/m²) hospitalized for HTNE, defined as systolic blood pressure (SBP) > 180 mmHg or diastolic blood pressure (DBP) > 120 mmHg with end-organ damage. PMTNs were measured in 47 patients, UMTNs were measured in 16 patients, and both PMTNs and UMTNs were measured in 15 patients.

RESULTS

PMTN/UMTN levels were not associated with SBP/DBP, comorbidities, end-organ damage, or interfering medications, the exception being that plasma normetanephrines (PNMNs) were significantly associated with comorbidities (Adj. R² = 0.16; p = 0.04) and interfering medications (Adj. R² = 0.15; p = 0.03), although with weak correlation. Marked MTN (specifically PNMN) elevations (647, 521, and 453 pg/mL; normal ≤ 148 pg/mL) were noted in only three patients (6%).

DISCUSSION

Marked MTN elevations in HTNE are uncommon. Therefore, we recommend against measuring MTN in the setting of an apparent precipitating cause of HTNE to avoid unnecessary testing and imaging. Testing for MTN in HTNE should be pursued only when there is no clear precipitating cause and in cases where there is strong underlying clinical suspicion for PPGL. However, should testing be performed, marked MTN elevations should not be disregarded as being a commonly occurring result of HTNE.

Inpatient Measurements of Urine Metanephrines are Indistinguishable from Pheochromocytoma: Retrospective Cohort Study

BACKGROUND

Pheochromocytoma is a rare cause of acute cardiovascular disease; however, any severe illness may have high catecholamines, simulating pheochromocytoma. We determined the spectrum of urine metanephrines from inpatient and outpatient collections without pheochromocytoma, compared with confirmed pheochromocytoma patients.

METHODS

Retrospective analysis using centralized laboratory data serving all outpatients and hospitals in southern Alberta. The analysis comprised 24-hour urine normetanephrine and metanephrine (UNM-UMN) results collected from hospital inpatients, community outpatients, and patients from a comprehensive provincial pheochromocytoma registry.

RESULTS

There were 974 unique inpatients (including 132 from intensive care), 6802 outpatients, and 58 pheochromocytoma patients. Among outpatient, general ward, and intensive care unit (ICU) patients, 18.7%, 34.4%, and 67.4% of results, respectively, were supranormal. Although pheochromocytoma patients had higher median UNM-UMN vs inpatients, there was substantial overlap. Receiver operating characteristic (ROC) analysis showed area under the curve (AUC) of 0.64-0.91 to detect true pheochromocytoma (P < .0001), with progressively poorer discrimination among hospitalized and ICU-dependent patients. A 24-hour urine normetanephrine >6.95 nmol/d had 98% specificity for pheochromocytoma when inpatient general ward samples were included, but only 46% sensitivity and 13% positive predictive value for pheochromocytoma. Considering ICU collections, 98% specificity required results more than fivefold above the upper reference limit and still had poor positive predictive value. A model combining both UNM and UMN results as a cross-product marginally improved the ROC AUC, but improved sensitivity in outpatients and ward patients but not ICU patients.

CONCLUSION

There is a high degree of overlap in UNM-UMN between hospitalized patients and pheochromocytoma; high test specificity is not achieved in this population unless >3-5 times the upper reference limit.

The relationship between QT interval and ventricular arrhythmias in acute myocardial infarction

Out of a total of 947 patients admitted to the CCU at Serafimerlasarettet during 2 years, all those with AMI and vintricular fibrillation (VF) or ventricular tachycardia (VT) during the CCU stay were selected. The QT interval could be measured in 15 patients with VF and 12 with VT before the event. The QT interval was also measured in two control groups; one consisted of 27 consecutively admitted patients with AMI without ventricular arrhythmias (VA), the other of 27 non-AMI patients treated in the CCU. Most patients in the group with VA showed pathologically prolonged QT intervals and there were statistically significant differences between this group and the control groups regarding corrected mean QT intervals. If these findings are confirmed, QT measurements might be of value in the prediction of malignant VA in AMI.

Potential role and mechanisms of subcellular remodeling in cardiac dysfunction due to ischemic heart disease

Several studies have revealed varying degrees of changes in sarcoplasmic reticular and myofibrillar activities, protein content, gene expression and intracellular Ca-handling during cardiac dysfunction due to ischemia-reperfusion (I/R); however, relatively little is known about the sarcolemmal and mitochondrial alterations, as well as their mechanisms in the I/R hearts. Because I/R is associated with oxidative stress and intracellular Ca-overload, it has been indicated that changes in subcellular activities, protein content and gene expression due to I/R are related to both oxidative stress and Ca-overload. Intracellular Ca-overload appears to induce changes in subcellular activities, protein contents and gene expression (subcellular remodeling) by activation of proteases and phospholipases, as well as by affecting the genetic apparatus, whereas oxidative stress is considered to cause oxidation of functional groups of different subcellular proteins in addition to modifying the genetic machinery. Ischemic preconditioning, which is known to depress the development of both intracellular Ca-overload and oxidative stress due to I/R, was observed to attenuate the I/R-induced subcellular remodeling and improve cardiac performance. It is suggested that a combination therapy with antioxidants and interventions, which reduce the development of intracellular Ca-overload, may improve cardiac function by preventing or attenuating the occurrence of subcellular remodeling due to ischemic heart disease. It is proposed that defects in the activities of subcellular organelles may serve as underlying mechanisms for I/R-induced cardiac dysfunction under acute conditions, whereas subcellular remodeling due to alterations in gene expression may explain the impaired cardiac performance under chronic conditions of I/R.

Effect of repeated regional myocardial ischemia in the rat heart on reperfusion arrhythmias and release of norepinephrine

We tested the hypothesis that repetitive regional myocardial ischemia in the rat could decrease reperfusion ventricular arrhythmias, possibly acting by diminished release of norepinephrine. Isolated perfused working rat hearts were pre-labeled with tritiated norepinephrine (NE3H). The efflux of 3H-labeled compounds was measured in the effluent coronary flow. Each heart was subjected to two consecutive periods of regional myocardial ischemia induced by ligature of the left coronary artery. The duration of the first ischemic period was 5 or 10 min and that of the second was 10 min. Serious rhythm disturbances did not occur during the first period of ischemia but did after reperfusion. The amount of NE3H liberated during the reperfusion period was more marked after an initial ischemic period of 10 min than after 5 min of ischemia. Reperfusion arrhythmias were of little importance after 5 min of ischemia but developed in a sustained pattern when reperfusion followed 10 min of ischemia. After 5 min of ischemia, the mean duration of reperfusion arrhythmias was 12.8 +/- 10.4 s during the first 3 min of reperfusion, but after 10 min of ischemia the mean duration of serious rhythm disturbances was 149.7 +/- 16.7 s. Reperfusion after the second 10-min occlusion increased the release of NE3H. In series 5-10, the percentage of NE3H compared with the total radioactivity was a mean of 71.4 +/- 3.3% during the 5 min of ligature, 79.0 +/- 5.3% during the first 3 min of reperfusion. During the 10-10 series in which the ligature was maintained for 10 min, the percentage of NE3H compared with the total radioactivity was 70.6 +/- 5.1%, 81.1 +/- 8.7% during the first 3 min of reperfusion. These results show no reduction of any catecholamine release or of reperfusion arrhythmias by repetitive regional ischemia and provide no evidence for any preconditioning effect after short periods of regional ischemia. The antiarrhythmic effects of repetitive myocardial ischemia such as preconditioning previously reported may depend on the exact protocols used.

The effect of timolol given five minutes after coronary occlusion on plasma catecholamines

The reported study determined whether timolol would afford a protective effect by preventing the coronary occlusion-induced arrhythmias associated with the increase in plasma norepinephrine (NE) and epinephrine (E). Ten anesthetized cats received saline or timolol (5 mg/kg, IV) five minutes after coronary occlusion of the left anterior descending coronary artery 10 to 14 mm below its origin. Coronary occlusion produced arrhythmia in three of the cats that received saline and in four of the cats that received timolol. Three of the saline-treated cats died in cardiogenic shock; two were sacrificed six hours postocclusion. Four of the timolol-treated cats died in congestive heart failure postcoronary occlusion. There was a gradual increase in NE (P greater than .05) and E (P less than .05) in both groups after coronary occlusion. Death produced a significant increase in NE and E levels. Timolol did not modify the occurrence of arrhythmias and the associated increase in plasma NE and E that developed after coronary occlusion and at death.

Possible interaction of platelets and adrenaline in the early phase of myocardial infarction

It is known that in most cases of transmural acute myocardial infarction a platelet clot originates within a coronary artery. In acute myocardial infarction patients increased levels of the plasma catecholamines adrenaline and noradrenaline as well as the platelet release proteins platelet factor 4 and beta-thromboglobulin have been reported. In this study, significantly higher values were found of platelet factor 4 (P less than 0.0001) and beta-thromboglobulin (P less than 0.002) in 17 acute myocardial infarction patients as compared to 17 control patients (on intensive care due to non-cardiac disorders), while the plasma levels of adrenaline and noradrenaline were not different. Positive correlations were obtained between the two catecholamines and the platelet products in the control group and between adrenaline and both platelet factor 4 (r = 0.715, P less than 0.01) and beta-thromboglobulin (r = 0.547, P less than 0.05) in the acute myocardial infarction patients. The data suggest that a stimulation of the platelets by adrenaline may facilitate in vitro activation during sampling in patients with high catecholamine load. On the other hand, a "preactivation" of the platelets by an increase of adrenaline might be of significance for thrombus formation in acute myocardial infarction.

The effect of beta blockers on cardiac neural discharge associated with coronary occlusion in the cat

The effect of timolol on postganglionic cardiac sympathetic neural discharge, blood pressure, heart rate, and rhythm changes associated with acute coronary occlusion of the left anterior descending artery was examined and compared with the effects of the beta blockers practolol and metoprolol. Timolol (5 mg/kg, IV) was infused 15 minutes prior to coronary occlusion in cats anesthetized with alpha-chloralose. Control heart rate fell from 129 +/- 10 to 106 +/- 2 one minute prior to coronary occlusion and remained at 106 +/- 2 beats/minute in the minute prior to arrhythmia. Control blood pressure fell from 126 +/- 20 to 91 +/- 19 and stabilized at 99 +/- 19 mm Hg one minute prior to coronary occlusion. Mean time to arrhythmia and death was 4.7 +/- 2.3 and 68.0 +/- 51.0 minutes (P greater than .05 vs no drug), respectively. Three cats died and two were sacrificed six hours after coronary occlusion. Blood pressure fell to 86 +/- 20 mm Hg two minutes after coronary occlusion, rose to 95 +/- 23 mm Hg at ten minutes, and remained there for ten minutes. Timolol did not alter postganglionic cardiac sympathetic neural discharge prior to coronary occlusion. Two minutes after coronary occlusion, mean postganglionic cardiac sympathetic neural discharge was 128 +/- 27 and increased to 139 +/- 36 impulses/second (% control) 4 minutes after coronary occlusion. A similar trend was found for the data recorded in 15 nerves (eight cats) in which coronary occlusion was initiated without timolol. The data suggest that a difference exists among beta blockers because prior to coronary occlusion, the cardioselective drugs metoprolol (1, 5, and 10 mg/kg, IV) and practolol (8 mg/kg, IV) depressed postganglionic cardiac sympathetic neural discharge whereas noncardioselective timolol did not. Because all three beta blockers increased the times to arrhythmia and death (although the increase was significant only after metoprolol and practolol), the acute protective mechanism does not appear to be due primarily to a depression of spontaneous sympathetic neural discharge.

Renin and the complications of acute myocardial infarction

To determine whether plasma renin activity in addition to catecholamines could be used as risk indicators, these parameters were measured in 19 patients with acute myocardial infarction. During the course of hospitalization, five patients developed ventricular fibrillation and three, cardiogenic shock. On admission, heart rate, plasma norepinephrine, epinephrine, and renin levels of these eight patients were significantly higher than those of the other patients with uncomplicated course. Peak creatine kinase MB activity was positively related to initial plasma renin activity (r = 0.62, p less than 0.01). Thus, the patients with the highest sympathetic activity following an acute myocardial infarction also had the highest plasma renin levels. They seem particularly prone to develop large infarcts and life-threatening complications.

Role of beta-adrenoreceptor antagonism in the prevention of reperfusion ventricular arrhythmias: effects of acebutolol, atenolol, and d-propranolol on isolated working rat hearts subject to myocardial ischemia and reperfusion

The role of catecholamines in the genesis of ventricular arrhythmias during the reperfusion period following coronary occlusion remains incompletely understood. An isolated rat heart preparation, free from the influence of autonomic innervation or of circulating catecholamines, was used to assess the effects of beta-adrenoceptor blockade. The hearts were prelabeled with tritiated norepinephrine ( NE3H ), and the total radioactivity and that in NE3H were measured in the effluent coronary flow. The left main coronary artery was ligated for 10 minutes after which reperfusion followed. The liberation of NE3H and the development of ventricular tachycardia and fibrillation were monitored throughout. The cardioselective beta-antagonist agent, acebutolol, in a high concentration (1.1 X 10(-4)M), had good beta-antagonist effect in response to the added isoproterenol (10(-6)M); this concentration of acebutolol also suppressed sustained reperfusion ventricular arrhythmias but unexpectedly increased the release of NE3H . Atenolol, another cardioselective agent, did not prevent reperfusion ventricular arrhythmias even in a high concentration of 40 mg/L (1.5 X 10(-4)M). The d-isomer of propranolol, with poorer beta-antagonist properties than the l-isomer, prevented such ventricular arrhythmias in a concentration of 1.3 X 10(-5)M, which was low when compared to that of atenolol. It is proposed that the beta-antagonist activity of the compounds tested could not explain the inhibition of reperfusion ventricular arrhythmias and that another quality such as membrane-stabilizing activity may be involved.

Potential oxidative pathways of catecholamines in the formation of lipid peroxides and genesis of heart disease

Effects of vitamin E, a fat soluble antioxidant, on the isoproterenol-induced changes in the lipid peroxide activity as determined by a quantitation of malondialdehyde (MDA) content in the myocardium were examined. Isoproterenol treatment (80 mg/kg given over two days in two equal doses) caused more than 100 percent increase in the MDA content which was prevented by pretreatment of the animals with vitamin E (alpha-tocopherol acetate, 10 mg/kg) for two weeks. Animals maintained on vitamin E deficient diet for 8 weeks were found to be more sensitive to isoproterenol-induced increase in the MDA content. A small increase in MDA content was also seen due to vitamin E deficiency alone. These changes were found to be reversible upon a 2 week feeding of the animals on the normal diet coupled with vitamin E treatment. Based on these data it is proposed that free radical mediated increase in lipid peroxide activity may have a role in catecholamine-induced heart disease.

Myocardial infarction. Changes in the concentrations of high-energy compounds and free amino acids in erythrocytes

Quantitative determination of the nucleotides AMP, ADP, ATP, GTP, NAD, NADP, 2,3-DPG and the free amino acids Lys, His, Gly, Ala, Val, Met, Phe, Tyr, Pro, Thr, Ser, Glu, Asp in erythrocytes was carried out in early and late stages of myocardial infarction. It was found that in erythrocytes, in the early stage of myocardial infarction, the concentrations of AMP, NADP and 2,3-DPG increased, whereas those of ADP, ATP, GTP and NAD decreased. In the third week of the disease the concentrations of AMP, ADP, NADP, and especially 2,3-DPG remained high, while those of ATP and GTP shifted towards the control. The concentrations of His, Gly, Ala, Val, Met, Phe, Thr and Glu increased, while those of Tyr, Ser and Asp decreased in the first stage of myocardial infarction. At the later stage of the illness (21 days) the concentrations of free amino acids returned to normal.

Protective effect of sulfinpyrazone against catecholamine metabolite adrenochrome-induced arrhythmias

Single intravenous injection of adrenochrome (10 to 50 mg/kg body weight), an oxidation product of catecholamines, has been shown to induce arrhythmias and cause death in anesthetized rats in a dose-dependent manner. Sulfinpyrazone, which is an inhibitor of platelet aggregation, was found to protect animals from these adrenochrome effects. It is suggested that sudden death due to arrhythmias in patients following the first attack of myocardial infarction of during other stressful situations may be linked to the formation of adrenochrome from abnormally high catecholamine levels in blood. Furthermore, results presented here also suggest that the reduction in the mortality rate of patients on sulfinpyrazone therapy may involve an antiarrhythmic property of the drug.

Serial plasma catecholamine response early in the course of clinical acute myocardial infarction: relationship to infarct extent and mortality

Clinical and experimental evidence suggest that sympathoadrenal activation contributes to mortality in patients with ischemic heart disease. To determine the level of sympathoadrenal activation in the very early phase of acute myocardial infarction (AMI) and to determine if location of infarction (anterior versus inferior) was related to sympathoadrenal activation, we studied norepinephrine (NE) and epinephrine (E) within 4 hours after the onset of symptoms and prior to any rise in plasma creatine kinase (CK). Mean (+/- SE) initial (NE = 591 +/- 111 pg/ml and E = 73 +/- 19 pg/ml), peak (NE = 1356 +/- 178 and E +/- 1098 +/- 608) and average (NE = 815 +/- 142 and E = 252 +/- 68) plasma catecholamine concentrations were considerably above normal (NE = 228 +/- 10 and E = 34 +/- 2 pg/ml, n 60) and values were similar for inferior and anterior infarctions. During an 18-month follow-up, three patients died in whom the AMI mean NE and E and peak CK were higher than in the eight late survivors. Thus the three AMI patients with peak EP values greater than 1000 died, whereas the eight AMI patients with peak EP values less than 1000 survived (p less than 0.01). The magnitude of sympathoadrenal activation early in the course of clinical AMI appeared related to the extent of myocardial damage and late mortality.

Plasma catecholamines in acute myocardial infarction

Plasma catecholamine levels were determined in 26 cases of uncomplicated myocardial infarction within 24 hours of onset of acute chest pain. Blood samples were collected at time of entry and at 4-hour intervals during the 48 hours following admission. Average values of plasma catecholamines within 1 hour of onset of pain were 0.87 ng./ml +/- 0.21 and remained elevated during the first 24 hours period. A gradual fall in catecholamine values was observed during the second 24-hour period. Catecholamines were higher in patients with sinus tachycardia and lower in patients with sinus bradycardia, and were higher in patients with anterior or anterolateral infarction. Catecholamine values were significantly higher when determined while patients presented ventricular ectopic beats or ventricular tachycardia. Sinus tachycardia, ventricular arrhythmias, and elevated plasma catecholamine values may be considered indicators of pain, anxiety, and/or left ventricular dysfunction without necessarily being causally related between themselves.

The urinary excretion of 3-methoxy-4-hydroxyphenylglycól in acute myocardial infarction

Urinary excretion of 3-methoxy-4-hydroxyphenylglycol (MHPG), noradrenaline, adrenaline and vanillylmandelic acid (VMA) was studied in 30 patients with acute myocardial infarction. The excretion of MHPG was higher in patients with myocardial infarction than in the control group, with no difference between uncomplicated and complicated courses of the disease. The excretion of MHPG showed a negative although not significant correlation with noradrenaline and VMA during the first days of infarction and a statistically significant positive correlation on the 5th day of the disease. The possible causes of the changes observed are discussed.

The effect of beta-adrenoreceptive antagonists on the morbidity and mortality in cardiovascular disease

The effect is critically reviewed of chronic administration of beta-adrenoreceptor antagonists on morbidity and mortality in angina pectoris and myocardial infarction. There is inconclusive evidence that the abrupt cessation of therapy with these agents may increase morbidity and mortality in angina pectoris. The type of anginal patient in which this may occur is not yet defined and neither is the mechanism. There is no evidence that beta-antagonists prolong the life of anginal patients. In the acute phase of experimental myocardial infarction, these drugs reduce mortality but do not do so in man. There is increasing evidence that they prolong life if administered to patients surviving the acute phase of myocardial infarction. The need for further studies is discussed.

Metabolism of free fatty acids, glucose and catecholamines in acute myocardial infarction. Relation to myocardial ischemia and infarct size

The myocardial metabolism of free fatty acids, glucose and catecholamines is reviewed in relation to current trends in the therapy of experimental myocardial infarction. Major modifications in the metabolism of free fatty acids, glucose and catecholamines have already been found after acute myocardial infarction in man, and animal experimental data suggest that such metabolic changes might play a role in the modification of infarct size and sometimes in the development of arrhythmias. However, animal experiments often represent extreme situations and the therapeutic use in man of agents to modify the metabolism of free fatty acids, glucose or catecholamines after myocardial infarction needs intensive investigation before general application. The sum total of the evidence from animal experiments suggests that increased circulating concentrations of free fatty acids and catecholamines, if sufficiently high, may be harmful rather than helpful to the outcome of acute myocardial infarction, and that increased provision of glucose (as glucose, insulin and potassium) may be beneficial. Reservations to these conclusions are that the concentrations used appear to be important factors in catecholamine and free fatty acid effects, and that the mechanism of action of glucose-insulin-potassium is more complex than originally thought.

Serial determination of plasma catecholamines in myocardial infarction

By the use of a precise and sensitive double-isotope derivative technic, plasma catecholamine concentration was measured at 2-hour intervals in 10 patients during the first 48 hours of myocardial infarction.

Plasma catecholamine concentration was elevated in most patients, but to an extremely variable degree. In each patient, however, the values were rather stable during the study period. High levels of plasma catecholamines were correlated to the clinical state of the patients. Patients who received antiarrhythmic treatment on admission to the hospital had higher values than untreated patients. There was no temporal correlation between plasma catecholamine concentration and ventricular arrhythmias. In contrast to the plasma catecholamine level, the heterotopic ventricular activity declined spontaneously in the untreated patients within the study period.

It is emphasized that the plasma catecholamine concentration in patients with acute myocardial infarction is considerably lower than the level necessary to produce arrhythmias in experimental myocardial infarction.