High levels of the circulating form of parathyroid hormone do not inhibit in vitro erythropoiesis.

Either primary or secondary hyperparathyroidism may be associated with anemia. The pathogenesis of this anemia remains obscure, but parathyroid hormone may directly suppress erythropoiesis or anemia may result from myelofibrosis. Previously reported in vitro studies of a direct inhibitory effect of PTH on erythroid progenitor growth were carried out with crude hormone preparations and appeared nonspecific. We have studied simultaneously the in vitro effects of pure (greater than 6000 U/mg) and crude (130 U/mg) preparations of PTH on murine and human hematopoietic progenitor growth. Increasing concentrations (2.5 to 20 U/ml) of crude PTH produced a dose-dependent inhibition of early erythroid (BFU-E) and granulocyte/macrophage progenitor (CFU-GM) growth in human and mouse marrow cell cultures. However, the biologically active N-terminal fragment containing amino acids 1-34 and the pure intact molecule of 84 amino acids failed to significantly inhibit hematopoietic colony growth. These observations demonstrate that in vitro inhibitory effects described with parathyroid gland extracts are not specific for erythropoiesis and may not be related to the circulating form of PTH.