Ultradian-infradian variation of cardiac creatine phosphokinase (CPK) activity in male Holtzman rats

Reference standards were sought for use in the search of any indications of myocardial damage by an alteration of the time structure, or chronome, of creatine phosphokinase (CPK) 'MB' isoenzyme activity in the heart of the male Holtzman rat. 144 rats were kept on 6 lighting regimens staggered by 4 hours, 24 rats per chamber. On 8 consecutive days, hearts from 3 animals from each chamber were harvested and weighed. The left ventricle was dissected, homogenized in a buffer solution at 4°C and stored frozen at -20°C until analysis. A supernatant aliquot of each sample was analyzed by a discontinuous gradient elution from DEAE-Shephadex A-50 columns. The CPK isoenzymes were quantified by the Rosalki method. Results of the CPK assay from each time point were analyzed by linear and nonlinear least-squares rhythmometry. Among other components, a 168 h or circaseptan rhythm characterized CPK activity in the heart of Holtzman rats. This component and other ultradian and circadian aspects of the time structure of rhythms and trends, the chronome of a given variable, may serve, by any eventual alteration of their dynamic characteristics, as gauges of potential cardiac damage prior to the occurrence of an increase in the overall mean of the enzymatic activity.