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.

Infradian modulation of liver nucleic acid and lipid content of adult female Lewis/S rats.

Infradian modulation with periods of 168 h and 120 h characterizes the RNA, DNA and lipid content of the liver in adult female Lewis/S rats. Multilinear analysis shows that the fit of an infradian cosine curve with these periods is statistically significant below the 5% level (P = 0.011; P = 0.