Effect of insulin on murine megakaryocytopoiesis in a liquid culture system.

To examine the influence of insulin on megakaryocytopoiesis, we tested its effect on murine bone marrow cultures in a liquid culture system. In the presence of pokeweed mitogen-stimulated spleen cell conditioned medium in culture, insulin markedly enhanced megakaryocyte colony formation and increased the number and size of free megakaryocytes seen after 7 days. Many of the cells in cultures with insulin, however, were classified as immature, since they had a basophilic cytoplasm, a low cytoplasmic/nuclear ratio and low acetylcholinesterase activity. It is suggested that insulin potentiates murine marrow megakaryocytopoiesis in vitro, but that this is not accompanied by differentiation of the cells from the immature to mature state.