CREATINE KINASE SUBFORMS IN MARATHON RUNNERS 843

Abstract

The lack of a rapid diagnostic marker specific to acute myocardial infarction (AMI) led to the development of a new high-voltage electrophoresis assay that separates creatine kinase (CK)-MB isoenzyme into its subforms. MB1 and MB2. The ability of the assay to detect early increases in the MB2/MB1 ratio in the blood and to reliably detect AMI within 6 hrs after the onset of chest pain has been shown to provide improved diagnosis of AMI. Positive clinical diagnosis is met when both the MB2 levels and subform ratios are positive (MB2≥2.6 U/L and ratio ≥ 1.7). Limited research has been conducted on the effectiveness of this assay on physically active individuals. Thus, the purpose of this study was to investigate the temporal patterns of MB subforms in plasma of marathon runners. Blood samples were obtained from 33 subjects (22 men, 11 women) prior to, immediately post, and 2.4, and 6 hrs post marathon race. Plasma MB2 activity, MB1 activity, MB2/MB1 ratio. CK-MB, and relative index (CK-MB/total CK) prior to the race were all within normal. Plasma MB2 activity, MB1 activity, and MB2/MB1 ratio immediately post race (3 to 5 hrs after race start) were elevated to clinically abnormal levels. Ninety% (30/33), 94% (31/33) and 100% of the subjects demonstrated a combined positive MB2 level and subform ratio immediately post, and 2 and 4 hrs post race. The kinetics of enzyme release in marathon runners is similar to that previously reported for AMI patients;acute acute skeletal muscle injury results in the release of tissue subforms of MB approx. 3 hrs after the onset of injury. These data suggest that the MB2/MB1 ratio cannot be used to differentiate between damage to the skeletal muscle vs the myocardium. Relative index values (<5%) across time suggest that skeletal muscle is the site of injury because values are less than that previously reported in AMI.