Effect of hormones and growth factors on alkaline phosphatase activity and collagen synthesis in cultured rat calvariae

Abstract

Studies on the direct effects of hormones and growth factors on bone alkaline phosphatase have been limited to parathyroid hormone (PTH) and 1,25 dihydroxyvitamin D3 [1,25(OH)2D3] and have not been compared to other parameters of bone formation. Insulin, PTH, 1,25(OH)2D3, epidermal and fibroblast growth factors (EGF, FGF) were examined for their effects on alkaline phosphatase activity and type I, [alpha 1 (I)]2 alpha 2, collagen synthesis in cultures of 21-day fetal rat calvariae. After 24 hr and 96 hr of treatment, insulin increased whereas PTH, 1,25(OH)2D3, EGF and FGF inhibited calvarial alkaline phosphatase activity and the incorporation of 3H-proline into collagenase-digestible protein and type I collagen. The agents tested did not affect the release of alkaline phosphatase into the culture medium. Although type I collagen was the only collagen detected, a small amount of another collagen might have been also synthesized. The hormonal effects on alkaline phosphatase activity and type I collagen synthesis were of greater magnitude after 96 hr than after 24 hr of continuous exposure to the agents tested and the two parameters correlated well (r = 0.88 after 96 hr and r = 0.97 after 24 hr of treatment. These studies indicate that insulin increases bone alkaline phosphatase activity and type I collagen synthesis in calvariae whereas PTH, 1,25(OH)2D3, EGF and FGF have an inhibitory effect. The results suggest that these agents affect osteoblastic function.