Circadian reference values for hematologic parameters in several strains of mice.

The circadian rhythms in the numbers of circulating formed elements in the peripheral blood were studied in 712 CD2F1, 188 BDF1, and 250 Swiss Webster mice kept under a lighting regimen of LD 12:12 (L 0600 to 1800 hr), a room temperature of 21 +/- 1 degree C, and food and water available ad libitum. The circadian rhythms were evaluated by the single cosinor procedure. The rhythm parameters--mesor, amplitude, and acrophase--the percentage of total variability attributable to the circadian rhythm, and the extent of the circadian rhythm are presented as guidelines for experimental design and evaluation. Under the conditions of this study, the mice of all three strains and both sexes show circadian variations, which are similar in their timing, in their red and white cell parameters. The percent of the total variance attributable to the circadian rhythms of each function varies between the strains studied in our laboratory being lowest in the Swiss Webster female mice. The extent of the circadian variation as expressed by the double amplitude as percent of mesor is similar in the three strains and between males and females. In relation to rest and activity spans, the hematologic circadian time structure in the nocturnally active mouse is different from that in diurnally active human subjects. The red-cell parameters show an acrophase in the middle of the rest span instead of the middle of the activity span as in human subjects. The lymphocytes and eosinophils in the mouse show an acrophase during the rest span that is similar to human subjects. In contrast to human subjects, however, neutrophils and monocytes show their acrophase in the first half of the rest span rather than during the second half of the daily activity span. The circulating formed elements in the peripheral blood thus follow a different circadian timing in the mouse than in human subjects; this has to be kept in mind when the time structure of the two species is compared, e.g., in models for experimental chemotherapy.