Creatine kinase in hypo- and hyperthyroid rats under consideration of the circadian oscillations.

Thyroxine level (T4) and total creatine kinase-activity (CK) were measured in serum samples from male Wistar-rats to investigate the relationships of serum titers after exposure to cold and thyroidectomy (TX). 72 hours exposure to cold (10 degrees C) produced a statistically significant elevation of T4 and a diminuation of CK-activity. In contrast to this protocol, TX (90 days after operations) reduced the T4 level and enhanced the CK-activity. These reactions were likewise statistically significant. The presented results are in agreement with the previous proposal which consists in inverse correlation between the T4 level and the CK-activity at hypo- and hyperthyroid states. Additionally it was shown that the highest activity of the serum CK appears in the first half of the light phase of the day under normal ambient temperature (24 degrees C) as well as under exposure to cold (10 degrees C).