Effects of hypergravity on proliferation and differentiation of osteoblast-like cells.

We investigated the effects of hypergravity on DNA synthesis and alkaline phosphatase (ALP) activity in cloned osteoblast-like cells. MC3T3-E1. Hypergravity (5 × g) stimulated DNA synthesis in these cells in a time-dependent manner and increased it approximately up to 150% of that of the control (1 × g). 12-O-Tetra-decanoylphorbol-13-acetate (TPA), a protein kinase C activator, and insulin-like growth factor I (IGF-I) enhanced DNA synthesis additively with hypergravity (5 × g). An increase in ALP activity induced by 10% fetal calf serum (FCS) was suppressed by hypergravity (2 × g, 5 × g). Five × g completely suppressed the increase in ALP activity. TPA and hypergravity (2 × g) suppressed the increase in ALP activity induced by FCS additively. Hypergravity (5 × g) showed no significant effect on cAMP nor cGMP production in these cells, but increased prostaglandin E2 (PGE2) production. Exogenous PGE2 stimulated DNA synthesis in these cells but had little effect on 10% FCS-induced ALP activity.