Cyclic hematopoiesis in grey collie dogs: a stem-cell problem.

Studies were made to ascertain the possipetition for a limiting number of pluripoble basis of cyclic hematopoiesis in the tential stem cells with the alternating grey collie. The results of 3H-thymidine competitive pressure provided by activaand “Fe labeling in conjunction with other tion and deactivation of a neutrophil feedmarrow parameters and peripheral counts back circuit from periphery to stem cell. suggest that the regular periodicity of This mechanism can account for the charblood neutrophil and reticulocyte levels acteristic 12-day periodicity and conis caused by a defect at the stemtributes to the phase difference in the cell-marrow interface. It is postulated cycling pattern of neutrophils relative to that the ebb and flow of hemic cell reticulocytes. production in the grey collie reflects corn-