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.

No abstract

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.

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<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<0.001 and p<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 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.