Cyclic hematopoiesis: effects of lithium on colony-forming cells and colony-stimulating activity in grey collie dogs.

The cycling of blood cell counts in grey collie dogs with cyclic hematopoiesis can be eliminated by treatment with oral lithium carbonate. To explore the mechanism by which lithium alters this stem cell disorder, studies of bone marrow granulocyte-macrophage progenitor cells (CFU-C), neutrophil colony-forming cells (neutrophilic CFU-C), and colony-stimulating activity (CSA) were performed. In untreated dogs, the proportions of CFU-C were found to fluctuate cyclically, but the cyclic fluctuations in neutrophil colony-forming cells were even more marked, with numbers decreasing to undetectable levels during each period of neutrophilia. Dogs on lithium, however, did not cycle the numbers of total or neutrophilic CFU-C. Tritiated thymidine suicide rates were not altered by treatment with lithium. Serum CSA levels and bone marrow cell elaboration of CSA were not increased by lithium. These studies suggest that lithium corrects cyclic neutropenia by a direct effect on the differentiation and proliferation of CFU-C; normalization of the proportion of CFU-C that enter neutrophilopoiesis appears to be an important effect of the lithium therapy.