Circadian rhythm in murine reticuloendothelial function.

Six separate groups, each composed of 15 comparable inbred female CBA mice, standardized in light daily from 0700 to 1900, alternating with darkness, maintained with food and water available ad libitum, were tested at 4-h intervals for a 24-h span for the phagocytic index, determined 3, 6, 9 and 12 min after the injection of a carbon suspension. By an analysis of variance and the single cosinor method applied to these data a circadian rhythm was demonstrated, with a double amplitude of 20% and an acrophase during the second half of the daily light span. These results extend the scope of immunologic circadian rhythms to the reticuloendothelial system as a feature of a bioperiodic defense mechanism, most active during the habitual rest light span of nocturnally active mice.