Diurnal variation of blood leucocytes in normal and adrenalectomized mice

In these experiments the normal variations in the absolute number and percentages of the blood leucocytes over a 24 hour period were studied in intact and adrenalectomized mice. 1. A diurnal variation of large magnitude occurs in the number of blood leucocytes obtained from the tail vein blood of mice. The diurnal cycle is characterized by high leucocyte levels during the late morning and early afternoon which is the least active period in this nocturnal animal, and by low levels during the late evening which is the most active period. 2. Although, large variations were observed for the absolute numbers of leucocytes, only minor variation were observed in the percentages of leucocytes present in tail vein blood during the normal diurnal cycle. The apparent diphasic nature of the total lymphocyte percentage curve can be explained by the inverse relationship between the normal and acytoplasmic lymphocytes. The percentage curve of the eosinophils resembles that of the acytoplasmic lymphocytes, and the percentage curves and absolute numbers of the stress lymphocytes and neutrophils are very similar. 3. Hemodilution or hemoconcentration does not appear to be a major factor in the leucocyte variations. Although a small day and night variation in hematocrit was observed it was not large enough to account for the magnitude of the leucocyte variations. 4. Adrenalectomy appears to abolish the diurnal variation of the circulating leucocytes since no day and night differences were observed in a 14 day period after the adrenal glands were removed. 5. The leucocyte count after adrenalectomy assumes levels which are characteristic for the high period of the normal diurnal cycle. A slight exception is noted for the eosinophils which maintain a level intermediate between normal high and low values and for the normal lymphocytes which show a slight lymphocytosis of these two periods. 6. The leucocyte variation during the diurnal cycle in mice correlate will with other indices of adrenal function. Since adrenalectomy abolishes these variation, it is apparent that they are mediated through the action of the adrenal hormones. Diurnal variations for eosinophils and total lylmphocytes have been observed in humans, and the eosinophil variations have been reported to be markedly reduced in Addison's Disease and panhypopituitarism. More work in needed, however, to work out the details of human leucocyte variations. Work of this nature would be a big aid in hematological diagnosis. 7. These results illustrate that in experimental work which is concerned with measuring changes in the number of circulating leucocytes, the interpretations of results must take into consideration normal diurnal variations or the data will reflect not only experimental differences but normal diurnal changes as well.