SUBCUTANEOUS transplantation of coarse powders of acid-insoluble matrix of the shafts of long bones of rat to allogeneic recipients results consistently in the formation of new bone through endochondral ossification1. Haematopoietic bone marrow develops in the newly formed ossicle in adolescent rats2,3 and this experimental model is amenable to an investigation of hormonal control of initiation of haematopoiesis. Erythropoiesis is dependent on pituitary hormones4,5 since hypophysectomy resulted in anaemia in all animal species which have been studied. Hypophysectomy caused a prompt regression of many stem-cell erythroblastic leukaemias in rat6. We now report the profound influence of hypophysectomy on de novo erythropoiesis in matrix-induced transformation ossicles.
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