Muscle ATP and lactate and the release of myoglobin and carbanhydrase III in acute lower-limb ischaemia.

Serum-myoglobin and carbanhydrase III (S-CAIII), a specific muscle enzyme, were measured on admission, during surgery and in the postoperative period in 23 patients with acute lower-limb ischaemia and in 21 patients with chronic limb ischaemia in order to evaluate these molecules as possible markers of the degree of clinical ischaemia. The muscle contents of ATP and lactate were determined in muscle biopsies from patients with acute ischaemia on admission. Unlike S-myoglobin and S-CAIII they discriminated between cases which required subsequent amputation from those which did not. Clinical signs of ischaemia were, however, of no value in this respect and there were no correlations between clinical signs or the duration of ischaemia and S-myoglobin or S-CAIII or the contents of ATP or lactate in muscle tissue. The levels of S-myoglobin and S-CAIII correlated well (r = 0.95, p less than 0.0001). In patients who subsequently required an amputation S-myoglobin increased ten-fold (i.e., from 24-48 h postoperatively in acute arterial ischaemia and from 3 h postoperatively in patients with chronic limb ischaemia). In patients with a successful revascularisation S-myoglobin returned to normal levels. It is concluded that in this investigation S-myoglobin had no prognostic value on admission and that S-myoglobin analyses in the postoperative course may be useful for making clinical decisions concerning impending recirculation failures.

Increase in serum parathyroid hormone levels after prolonged physical exercise.

Serum concentrations of parathyroid hormone (PTH), calcium, magnesium, phosphate and myoglobin were measured regularly during a 5-d recovery period in 17 men who had participated in a 7-d field exercise maneuver with intense physical activity. Immediately after the exercise, there was an increase in serum PTH levels of the same magnitude as the maximal rise during a hypocalcemic test. The rise in PTH was not related to changes in serum electrolytes, but was significantly correlated to an increase in serum myoglobin, indicating that those who performed the largest amount of work also experienced the greatest stimulus for secretion of PTH. There were no significant changes of the serum total calcium and only a small initial rise of the magnesium concentrations. Serum phosphate levels were greatly reduced and gradually returned during recovery. This study extends previous observations, from short-term investigations, that physical activity stimulates secretion of PTH.

Prolonged low-intensity exercise raises the serum parathyroid hormone levels.

Twelve healthy males performed 5 h exercise on a bicycle ergometer at a constant work load of approximately 50% of their maximum capacity. The serum concentrations of parathyroid hormone (PTH) increased after the first hour and were continuously elevated throughout the exercise period. The rise in PTH was 5-7% above pre-exercise levels, corresponding to 20-30% of the maximal increase obtained by the same assay during prolonged hypocalcaemia. The probable cause for the rise in PTH was that the plasma ionized calcium tended to be lowered during exercise. Since the total serum calcium concentrations were raised (by 3-5%) during exercise the reduction of the free, ionized, fraction was presumably largely due to increased complex-binding although an outward transport from plasma was not excluded. The serum concentrations of magnesium were gradually reduced during exercise while those of phosphate and potassium were raised throughout, probably as a result of leakage from the working muscle.

Muscle cell leakage of myoglobin after long-term exercise and relation to the individual performances.

Muscle protein release was studied during and after prolonged exercise by means of serum myoglobin determinations. Increased serum myoglobin levels were regularly found after performance of long-term exercise. The correlations (P less than 0.001) to muscle enzymes indicated nonselective release from muscle cells. Myoglobin measured after completed exercise was correlated to the finishing time in a ski race, i.e., the fast skiers showed lower myoglobin levels than slow skiers. Inexperienced skiers and also skiers older than 49 years of age were found to have higher myoglobin levels than the others although the mean finishing times were similar. Myoglobin measured during and after 5 h of bicycle exercise showed large differences even though the relative work load was identical. Myoglobin started to rise 1.2 h (median) after the commencement of the bicycle exercise. The time at which myoglobin started to rise correlated (P less than 0.01) with the myoglobin levels after completed exercise and was not related to the physical fitness of the individuals. The results indicated considerable individual differences with regard to muscle protein leakage during exercise. The leakage is not simply related to the individual's apparent physical fitness but probably also to constitutional factors, such as age and metabolic capacity of the muscle cells.

Myocardial and skeletal muscle function in habitual alcoholics and its relation to serum myoglobin.

Lower-than-normal serum myoglobin levels are regularly found in habitual alcoholics without recent alcohol intake and were also confirmed in this study. It was hypothesized that these low levels reflect reduction in myocardial and skeletal muscle function. To study this hypothesis, heart and skeletal muscle function was evaluated and related to serum myoglobin levels. Myocardial function evaluated by noninvasive techniques was significantly decreased and heart muscle mass increased (p less than 0.001) in circulatory asymptomatic alcoholics compared with age- and weight-matched healthy male control subjects. The working capacity of the alcoholics was lower than expected during dynamic exercise testing (p less than 0.001), and maximal muscle power was reduced during isokinetic muscle testing (p less than 0.05). Myoglobin levels were correlated to the degree of myocardial diastolic dysfunction (p less than 0.01) but not to working capacity during dynamic or isokinetic exercise testing. The observation that myocardial affection was related to low serum myoglobin suggests that the mechanisms behind reduced myoglobin release are linked to the chronic muscle affection in alcoholics.

Ethanol reduces myoglobin release during isokinetic muscle exercise.

Changes in serum myoglobin concentrations were studied in 12 healthy males performing a standardized isokinetic 2-min exercise test. The test was performed on three separate occasions: in the habitual state, during moderate ethanol intoxication and one day after ethanol intake. Although the performed muscle work, maximal heart rate, and blood lactate levels did not differ between the three test occasions, the serum myoglobin increments after exercise were significantly reduced (p less than 0.05) in the ethanol-intoxicated state and also 10-15 hours after ethanol intake. The reduction of the exercise-induced myoglobin increment was not explained by increased elimination of the protein. The mechanism, therefore, is likely to be a reduction of myoglobin release from skeletal muscle due to an ethanol-induced alteration of the muscle cell membrane, possibly by means of adenylate cyclase activation.

Serum myoglobin concentrations are decreased by beta-adrenergic stimulation.

During infusion with adrenaline in healthy subjects there was a more than 50% reduction in serum myoglobin concentrations. This effect appeared to be specific for beta-adrenergic stimulation, since no changes were seen after prior IV beta-blockade with propranolol, nor did noradrenaline affect the serum myoglobin levels. Oral beta-blockade with propranolol raised the basal serum levels of myoglobin and enhanced the exercise-related rise in serum myoglobin concentrations during ergometer cycling to exhaustion. These observations thus indicate that the beta-adrenergic system affects serum myoglobin concentrations. This should be kept in mind in the evaluation of myoglobin measurements for clinical purposes, and might reflect a physiologically relevant mechanism.

Myoglobin in rat hind limb muscles after denervation and during reinnervation.

Radioimmunoassay of myoglobin (Mb) was performed in rat hind limb muscles after surgical denervation and during reinnervation following cryolesion of the sciatic nerve. Muscles of the contralateral leg served as controls. After resection of the sciatic nerve, decreased Mb concentrations were noted on the fourth day in the tibialis anterior, peroneus longus, and extensor digitorum longus (EDL) muscles. Thereafter, the levels increased up to the last observation on day 32. The increases in Mb levels in the tibialis anterior and EDL muscles were considerably more pronounced (305% and 324%, respectively) than in the peroneus longus and soleus muscles (148% and 137%, respectively). After cryolesion of the sciatic nerve, the Mb concentrations in the tibialis anterior, peroneus longus, and EDL muscles increased, reaching maximal values on days 16-21. The levels then decreased and normal values were observed 2 months postoperatively. The normalization of the Mb levels during reinnervation corresponded fairly well in time with the clinical recovery and neurophysiological findings observed in a previous study.

Variations in serum myoglobin after a 2-min isokinetic exercise test and the effects of training.

Serum-myoglobin was measured after the completion of three different types of exercise i.e., dynamic, isometric, and isokinetic. The maximal rises in serum-myoglobin levels were 20%, 70%, and 300%, respectively. On the basis of this finding a 2-min isokinetic test was developed and standardized for the purpose of studying conditions in vivo that may affect myoglobin leakage from skeletal muscle cells. Fourteen healthy men performed the 2-min isokinetic test. Blood lactate increased on average eight times with maximal levels obtained 4 min after completed work. S-Myoglobin levels obtained 4 min after completed work. S-Myoglobin was raised approximately five times after 2 h. The rise in S-myoglobin was significantly (P less than 0.01) related to the loss in muscle strength (torque decline) during the test. After a training period of 3 weeks comprising 4 min of maximal isokinetic exercise three times a week the rise in S-myoglobin after a 2-min isokinetic test was reduced from on average 240 micrograms X 1(-1) to 96 micrograms X 1(-1) (P less than 0.001). The rise in blood lactate was not related to the variations in S-myoglobin or affected by training. The 2-min isokinetic exercise test is an easily standardized exercise test which in combination with measurements of serum-myoglobin should prove valuable in the study of conditions affecting leakage from muscle cells.

The value of serum myoglobin determinations in the early diagnosis of acute myocardial infarction.

Myoglobin has been measured in sera from 305 consecutive patients with suspected acute myocardial infarction (AMI) to study the clinical value in relation to other diagnostic methods. On admission the frequency of false negative (i.e. the diagnostic sensitivity) myoglobin values was 28% in the AMI group as compared with 60% for serum creatine kinase (CK) and 46% for serum aspartate aminotransferase (ASAT). Four hours after admission the corresponding figures were 2, 31 and 29%. This makes the diagnostic sensitivity of the myoglobin test 0.98, which is significantly higher (p less than 0.001) than that of the two enzyme tests. The predictive value of a negative myoglobin test was 0.97 and also significantly higher (p less than 0.001 and p less than 0.01) than for CK and ASAT. S-myoglobin was further related to the number of complications and the prognosis of the patients, and high levels appeared to be an unfavourable sign, particularly in combination with an anterior wall infarct. This study has demonstrated and confirmed the superior diagnostic sensitivity of myoglobin determination in early AMI. The inclusion of S-myoglobin in the routine diagnosis of AMI warrants serious consideration.

Radioimmunoassay of serum myoglobin in neuromuscular diseases.

Radioimmunoassay of serum myoglobin was performed in 85 patients with muscular symptoms. Elevated levels were found in 93% of patients with myogenic myopathy, in 54% with myasthenia gravis and in 50% with neurogenic myopathy. All 11 patients with polymyositis had elevated myoglobin concentrations. In six of seven patients with polymyositis, who were followed up with repeated determinations, a clear relationship between myoglobin levels and clinical course was found. In general serum myoglobin seemed to be a more sensitive indicator of muscle disease than creatine kinase.

Serum myoglobin in thyroid disease.

Serum myoglobin levels were measured longitudinally in patients undergoing therapy because of various thyroid disorders. Elevated myoglobin values - 72.6 (58.7-89.7) micrograms/l (mean +/- SEM) were found in group of hypothyroid subjects. The degree of myoglobin increase seemed related to the severity of hypothyroidism. When rendered euthyroid the myoglobin levels of these patients were normalized - 41.0 (37.3-45.1) micrograms/l. In patients with hyperthyroidism, due to Graves' disease or subacute thyroiditis (de Quervain), only minor changes of myoglobin values within the reference range of health subjects, were measured. This suggests that mechanisms not affecting myoglobin release are responsible for the muscular weakness of thyrotoxic patients.

Serum and urinary myoglobin in alcoholics.

The serum levels of myoglobin were measured in 106 male alcoholics. Subnormal levels were found in 31% of the alcoholics with no alcohol consumption for the last 2--4 weeks, while none of them had elevated levels. Of the alcoholics on ambulatory control and with varying current alcohol intake. 18% had increased levels compared to healthy controls. Serial myoglobin levels were determined in 19 patients following the cessation of heavy drinking sprees. Despite the fact that none of the patients had clinical evidence of acute myopathy, marked myoglobin elevations were noted in five patients; their serum levels gradually declined and normalized with 4--7 days. Comparing the three groups, similar frequencies of subnormal or elevated serum CK levels were observed. Myoglobin levels were not raised due to impaired glomerular filtration rates. No correlation was found between serum myoglobin and laboratory signs of liver affection. Although hypophosphatemia, hypomagnesemia and hypokalemia were occasionally noted, decreased serum electrolytes did not have any relation to elevated serum myoglobin. A transient, slightly increased urinary excretion of myoglobin parallel with increased excretion of beta 2-microglobulin was observed in 2/17 alcoholics, suggesting that instances of myoglobinuria in alcoholics with heavy recent drinking may be due to a transient minor tubular dysfunction.

Diagnosis, size estimation and prediction of acute myocardial infarction from S-myoglobin observations. A system analysis to assess the influence of various sources of variability.

Three different ways of using S-myoglobin observations for early diagnosis of acute myocardial infarction have been investigated by computer simulation techniques, viz. classification based on (i) single determination in relation to a decision limit, (ii) the peak serum concentration value, (iii) estimated or predicted value of infarct size from serial serum concentration determinations. The results of the in numero experiments indicate that it is possible to define optimal conditions with regard to time, period and frequency of observation, as well as to assess requirements on pre-analytical/analytical variation. The optimal time for a single observation should be about 10-12 h after onset of symptoms. The influence of pre-analytical/analytical variation is not very critical in this connection and the quality requirements are achievable in the clinical chemical laboratory today (total CV about 0.10). The peak serum value has good diagnostic power, but does not provide a good index of infarct size, no matter how good the analytical quality may be. It should be possible to predict infarct size from early serial S-myoglobin observations. A coefficient of pre-analytical/analytical variation below 0.05 is then required in addition to frequent blood specimen collection from admission up to peak time of the serum concentration curve.

Radioimmunoassays of human myoglobin in serum and urine.

Two solid-phase radioimmunoassays have been developed for the detection of myoglobin in serum and urine. The sensitivity of the methods is 0.1 and 0.5 microgram/l, respectively, with a coefficient of variation of the respective method of 7-8%. The mean serum concentration of myoglobin in ninety-nine healthy blood donors was 44.3 microgram/l +/- 18.0 microgram/l (SD) with a significant difference (P less than 0.001) between men (50.6 +/- 19.8) and women (35.7 +/- 10.4). Serum myoglobin was positively correlated to age (P less than 0.05), body weight (P less than 0.02), serum creatine kinase (P less than 0.001), and serum creatinine (P less than 0.001) to galactose elimination rate. Serum myoglobin levels were not influenced by exhaustive short time dynamic exercise. The mean urinary excretion of myoglobin in twenty-four healthy students was 1.2 microgram/24 h (range 0.1-4 microgram/24 h). Myoglobin excretion was correlated to excretion of beta 2-microglobulin (P less than 0.02) but not to serum levels of myoglobin. No indications of circulating antibodies to myoglobin were obtained when assaying sixty-seven rheumatoid arthritis and thirteen myastenia gravis sera. Presence of other myoglobin binding substances in serum, which would interfere with the assays also seemed unlikely. Determination of myoglobin in serum by sensitive and specific method might be of clinical value in the diagnosis of diseases involving muscle tissues.

Evaluation of urinary myoglobin assay test for myocardial infarction.

Serial determinations of urinary myoglobulin, beta2-microglobulin and albumin, and of serum myoglobin, were performed in twenty-eight consecutive patients admitted to a coronary care unit. Patients with myocardial infarction (MI patients) all had higher serum levels of myoglobin then those with other diagnoses (OBS patients). Myoglobinuria occurred in 80% of MI patients and in half of the OBS patients. The appearance of myoglobin in urine was mainly accounted for by an impaired renal reabsorption of low molecular weight proteins. Measurement of urinary myoglobulin, in contrast to serum myoglobulin, is of little value for the diagnosis of myocardial infarction.

Myoglobinemia after myocardial infarction; influence of renal function.

Using a solid-phase radioimmunoassay for detection of serum myoglobin, the pattern of myoglobinemia was investigated in patients with acute myocardial infarction. All patients with acute infarcts had a marked rise in serum myoglobin concentration. Peak serum myoglobin concentration was found on an average 9 h after the initial onset of chest pain. Late onset of myoglobin peaks without signs of reinfarction as well as sustained abnormal myoglobinemia, in the majority of patients, could be explained by impaired renal function. The peak serum level of myoglobin correlated (r = 0.92) to the peak level of ASAT supporting the idea that the detection of myoglobin in serum may be a useful diagnostic aid in the qualitative diagnosis of myocardial infarction.

Neutrophil and eosinophil granulocytes in bacterial infection: sequential studies of cellular and serum levels of granule proteins.

The intraneutrophilic concentrations of lactoferrin, myeloperoxidase, collagenase and chymotrypsin-like cationic proteins were measured sequentially during acute bacterial infection. The serum levels of lactoferrin and myeloperoxidase were also followed as well as the 'eosinophil' cationic protein as a marker for eosinophil leucocytes. During the early course of infection there was a profound but reversible decrease of intraneutrophilic lactoferrin. The levels of cellular collagenase and chymotrypsin-like cationic proteins also tended to decrease reversibly during day 2-8 in most cases; myeloperoxidase levels were normal except for two cases. Serum myeloperoxidase and lactoferrin correlated with blood neutrophil counts. In spite of the absence of peripheral eosinophils the 'eosinophil' cationic proteins of serum were increased on the first day of infection, which may reflect increased eosinophil turnover.

Myoglobin turnover--influence of renal and extrarenal factors.

The serum level of myoglobin, an LMW constituent of striated and myocardial muscle, has been studied in various clinical situations in order to obtain information about factors influencing myoglobin turnover. The myoglobin level was significantly correlated to different variables of GFR such as serum beta2-microglobulin, serum creatinine, and 51Cr-EDTA clearance. Following a successful renal transplantation rapid decrease in serum myoglobin was found parallel to increase in GFR's. In patients with advanced long-standing uremia, comparatively small elevations of serum myoglobin were seen when correlated to the degree of GFR reduction, demonstrating an influence of extrarenal factors on the myoglobin levels. The importance of extrarenal factors on the actual serum level of LMW proteins was also illustrated by serial studies on SLE patients receiving corticosteroid therapy. In these patients, elevations of serum myoglobin levels were found, but serum beta2-microglobulin levels gradually decreased during therapy. Finally, calculations based on curves of serum disappearance of myoglobin in patients with acute myocardial infarction indicate that only about 0.3 mg of myoglobin per day is released from the muscle pool during normal conditions, which suggests that myoglobin catabolism mainly occurs within the muscle tissue.