Effects of growth hormone and insulin-like growth factor-I on the proliferation and differentiation of cultured pig bone cells and rat calvaria cells.

Growth hormone (GH) increases bone formation in vivo in pigs. The capacity of GH and its mediator insulin-like growth factor-I (IGF-I) to influence bone cell proliferation and differentiation was investigated in cells isolated from trabecular and cortical bone of growing pigs, from fetal pig bone and from newborn rat calvaria. GH enhanced the proliferation of confluent rat cells but did not affect that of either confluent or subconfluent porcine cells from trabecular, cortical or fetal bone. IGF-I increased the proliferation of confluent rat cells and subconfluent pig cells. GH slightly inhibited alkaline phosphatase (ALP) activity in pig cells of the three origins while IGF-I increased it in cortical cells. Collagen synthesis by pig cells was stimulated by IGF-I but not by GH. These results suggest that GH does not stimulate bone forming cells in pigs, and that GH and IGF-I affect cultured bone cells differently depending on the species or bone type they were isolated from.