Activity of creatine kinase MB-isoenzyme in rat serum after heart irradiation and/or farmorubicin (4′-epidoxorubicin) treatment

Activity of creatine kinase (CK, EC 2.7.3.2) and its CK-MB isoenzyme were evaluated in rat serum after external irradiation of the heart with 20 Gy given as A single dose or 4 × 5 Gy and also after treating the animals with farmorubicin 10 mg/kg in a single dose or 4 × 2.5 mg/kg. Fractionated irradiation or repeated injection of farmorubicin induced high five-fold transient increment of CK-MB isoenzyme activity in rat serum. Combined treatment (4 × 5 Gy heart irradiation, week 1, after 2 days pause 4 × 2.5 mg/kg farmorubicin, week 2) showed increase of MB isoenzyme activity in serum roughly comparable with that measured in animals treated with farmorubicin alone. The behaviour of MB isoenzyme activity after single doses of radiation 1 × 20 Gy or farmorubicin 1 × 10 mg/kg was dissimilar to that after repeated doses and was generally lower. Specially, a high single dose of farmorubicin led at first to suppression of CK-MB isoenzyme activity and then to an increase, however, slower than after fractionated treatment. Generally, elevation of CK-MB isoenzyme activity in rat serum after heart irradiation and farmorubicin injection (scheme independent) was many times higher than the total CK activity increment. Results suggest that estimation of CK-MB isoenzyme activity in serum is more sensitive and definitive evidence of early cardiac damage exerted by gamma-rays and/or farmorubicin than total CK activity.