Modulation of type beta transforming growth factor activity in bone cultures by osteotropic hormones.

Abstract

Type .beta. transforming growth factor (TGF-.beta.) activity was found in conditioned medium harvested from fetal rat and neonatal mouse calvariae by using the anchorage-independent growth of normal rat kidney fibroblasts as an indicator system. Calvariae incubated with parathyroid hormone, 1,25-dihydroxyvitamin D3, and interleukin 1, all factors that stimulate bone resorption, showed a concentration-dependent increase in TGF-.beta. activity in the culture medium. Increases in TGF-.beta. activity persisted undiminished for 48 hr after removal of these factors. The increases in TGF-.beta. activity from the resorbing bone cultures were relatively greater than the increases in bone resorption. Calcitonin inhibition of bone resorption correlated with a decrease in TGF-.beta. activity. Thus, agents that modulate bone resorption also effect TGF-.beta. activity in the bone culture medium. Changes in local concentrations of TGF-.beta. activity by osteotropic hormones may be important in the regulation of normal bone remodeling.