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 w ere evaluated in rat serum after external irradiation of the heart wit h 20 Gy given as A single dose or 4 x 5 Gy and also after treating the animals with farmorubicin 10 mg/kg in a single dose or 4 x 2.5 mg/kg. Fractionated irradiation or repeated injection of farmorubicin induce d high fivefold transient increment of CK-MB isoenzyme activity in rat serum. Combined treatment (4 x 5 Gy heart irradiation, week 1, after 2 days pause 4 x 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 x 20 Gy or farmorubicin 1 x 10 mg/kg was dissimilar to that after repeated doses and was general ly lower. Specially, a high single dose of farmorubicin led at first t o suppression of CK-MB isoenzyme activity and then to an increase, how ever, slower than after fractionated treatment. Generally, elevation o f CK-MB isoenzyme activity in rat serum after heart irradiation and fa rmorubicin injection (scheme independent) was many times higher than t he total CK activity increment. Results suggest that estimation of CK- MB isoenzyme activity in serum is more sensitive and definitive eviden ce of early cardiac damage exerted by gamma-rays and/or farmorubicin t han total CK activity.