Growth plate stimulation by diaphyseal fracture. Autoradiography of DNA synthesis in rats.

Using autoradiography, I studied the effect of diaphyseal injuries on the DNA synthesis of growth plate cells in Swiss Albino rats and found that mitotic activity of germinal and proliferation zone cells of the growth plate and periosteal callus increased 24 hours after the fracture and peaked at 48 hours. The mitotic activity continued until the eighteenth day with gradual decline from the second day onwards. It appears as if the growth plate cells are stimulated by the same mitogenic activator as the periosteal cells. I therefore postulate that the overgrowth of long bones after fractures is due to local mitogenic stimulating factor(s), and is not due to an increased blood supply to the epiphyses, as is presently widely claimed.