Rapid renal clearance of immunoreactive canine plasma myoglobin.

Rates and mechanisms of myoglobin removal from plasma were examined in closed-chest dogs, using disappearance patterns of immunoreactivity and radioactivity after i.v. canine myoglobin radiolabeled with 125I. Arterial immunoreactive myoglobin concentration decreased monoexponentially over a 2-decade range, with rate constants of disappearance averaging -0.080 +/- 0.014 min-1 (+/- SD) (corresponding to half-times of disappearance of 8.9 +/- 1.5 min). Renal arteriovenous difference in immunoreactive myoglobin concentration documented extraction of the parent molecule, with extraction ratios averaging 0.36 +/- 0.06. Renal venous specific activity increased a few minutes after myoglobin administration, consistent with discharge from the kidney of nonimmunoreactive radiolabeled peptides of the parent molecule. Arterial disappearance of 125I was subsequently delayed in relation to immunoreactive myoglobin. Urinary recoveries of immunoreactive parent molecule and radiolabeled constituents were limited, averaging 2.5 +/- 1.1% and 12 +/- 1.1% over a 6-hour period. Arterial rate, constants of disappearance of immunoreactive myoglobin decreased markedly with decreases in renal perfusion produced by obstruction of renal arterial inflow. We conclude that myoglobin entering the vascular space is normally cleared rapidly by renal catabolism. Seven myoglobin concentration-time patterns during acute myocardial infarction directly reflect patterns of protein entry into the vascular space after release from injured tissue.