The kinetics of myoglobin in old volunteers and in patients with acute myocardial infarction.

Following pre-treatment with potassium iodide, [125I]myoglobin was administered intravenously to six old volunteers. Blood and urine samples were taken at regular intervals. Serum radioactivity was shown to be myoglobin-bound. Three rates of elimination were observed, with half-lives of 20 min, 3 h 20 min, and 18 h 30 min. The first two rates corresponded to distribution volumes of 5.2 and 211. The third rate was of zero order and had eliminated around 10% of administered radioactivity after 6 h. At this time 60% of administered radioactivity had been recovered from the urine. Around 80% appeared as non-protein bound 125I, while 10% was protein-bound. The latter fraction was not precipitable with antiserum against myoglobin, which suggests that this fraction was deconjugated globin. Only insignificant amounts were excreted as myoglobin. The elimination constants were larger than those found in patients with acute myocardial infarction (AMI), measured by the disappearance rate of endogenous myoglobin.