Calcium Homeostasis and Erythropoietic Control in the Rat

Abstract

When plasma calcium concentrations in the rat were elevated by injection of either calcium chloride or parathyroid hormone, there was an increase in mitotic activity in the bone marrow which led to an increase in reticulocyte production and radioactive iron incorporation in the peripheral blood. Thyroparathyroidectomy produced parallel decreases in plasma calcium, bone marrow mitosis, and erythropoiesis, a situation which could be reversed by the administration of parathyroid hormone or by calcium chloride injections. Since the calcium- or parathyroid hormone-induced stimulation of bone marrow mitosis also occurred in both nephrectomized and polycythemic rats, this mitogenic action was not due to a secondary release of renal erythropoietic factor or an activation of circulating plasma erythropoietin. In contrast to calcium and parathyroid hormone, (ovine) erythropoietin did not stimulate cell division in the bone marrow within 6 h of injection.