PHASE RELATIONS OF 24-HOUR PERIODICITIES IN BLOOD CORTICOSTERONE, MITOSES IN CORTICAL ADRENAL PARENCHYMA, AND TOTAL BODY ACTIVITY1,2

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Abstract
Under conditions standardized for analysis of 24-hour periodicity, with light from 06:00 to 18:00 alternating with 12 hours of darkness, corticosterone in mouse serum undergoes reproducible 24-hour changes, with peak blood levels at about 16:00. Significant differences in phase characterize the 24-hour rhythms in serum corticosterone and in mitoses of cortical adrenal parenchyma; under the same lighting conditions, the peak of the latter occurs at about midnight. The corticosterone rhythm leads in phase the rhythm in gross motor activity and lags behind the eosinophil rhythm, in the absence of intentional stimulation other than daily routine. As compared to the significant change in blood corticosterone level along a 24-hour scale, the immediate effect of audiogenic stimulation upon serum corticosterone is slight. It consists of a small rise following stimulation at the time of the daily "corticosterone low" and is negligible after stimulation at the time of "corticosterone high." The daily rhythm in blood level of adrenal 11-oxycorticoid in nocturnal mice, as compared to predominantly diurnal man is comparable in amplitude but differs in its environmental phase relations, indicating a species difference in mode of synchronization of rhythm.