Circadian variations in mouse bone marrow.

Circadian variations in mouse hemopoiesis were investigated in the early spring and summer using spleen colony assay, agar colony technique and differential counting. The multipotent stem cells and committed stem cells as well as the numbers of myelopoietic cells/femur underwent strong circadian variations with similar type of rhythmicity. In both types of stem cells (CFUS, CFUC) the rhythm was correlated to the variations in the numbers of myeloid cells/femur. Highest value (acrophase) was found at 1300 (MET). The amplitudes for CFUS and CFUC were between 50 and 80% of the 24 h mean values (mesor), whereas the variations in the other compartments of the bone marrow were less pronounced. For the CFUC the circadian rhythms were reproducible both at two different times of the year and over 48 h. Changes were found in erythroid cells as well, but the rhythm was not so pronounced.