Effect of selected drugs and myocardial infarction on the disappearance of creatine kinase from the circulation in conscious dogs

Abstract

Estimates of infarct size based on serial plasma creatine kinase (CK) changes have been made utilising the disappearance rate of CK from blood (k_d) as one parameter. This study was performed to evaluate the effects on CK disappearance of myocardial infarction per se and selected drugs often used in the management of patients with myocardial infarction. Fifty-six conscious dogs were studied. Canine myocardial CK was isolated and radioactively labelled. Experiments were performed with intravenous injections of unlabelled CK or with radioactively labelled material. After injection, plasma CK activity declined monoexponentially (r = −0.95, n = 30) exceeding the rate of CK disappearance in vitro in whole blood or plasma. Three successive daily determinations of k_d differed by ≤10% in the same dog (n = 5). Removal of radioactively labelled protein from plasma paralleled disappearance of plasma CK enzyme activity for several hours after i.v. injection of ¹⁴C–CK (n = 5). Myocardial infarction after occlusion of the left anterior descending coronary artery altered k_d by 14C–CK. Administration of large doses of Nembutal (30 mg·kg⁻¹), morphine (2 mg·kg⁻¹), or Valium (1 mg·kg⁻¹) decreased k_d markedly (n = 17), but low doses of morphine (0·2 mg·kg⁻¹) or Valium (0·1 mg·kg⁻¹) did not substantially diminish k_d. Thus, enzymatic estimates of infarct size are not likely to be influenced by changes in k_d occurring during myocardial infarction. However, modification of estimates may be required when pharmacological interventions are employed, capable of altering CK disappearance.