Anabolic effects of prostaglandins in cultured fetal rat calvariae: Structure-activity relations and signal transduction pathway

Abstract

The structure-activity relations and signal transduction pathways for the anabolic effects of prostaglandins were examined in cultured fetal rat calvariae. In the presence of cortisol prostaglandins of the E and F series (10⁻⁹ to 10⁻⁵ M) produced a dose-related increase in [³H]thymidine incorporation up to 4-fold at 24 h. Prostaglandin E₂ (PGE₂) was also effective in the absence of cortisol. Butaprost (10⁻⁶ M), a selective EP-2 receptor agonist, produced partial stimulation. Prostaglandin D₂, prostacyclin, sulprostone, an EP-1 and EP-3 receptor agonist, and fluprostenol, an FP receptor agonist, were ineffective. Forskolin (10⁻⁴ M) increased [³H] thymidine incorporation 3-fold, while phorbol myristate acetate (PMA) (10⁻⁶ M) produced a 1.8-fold increase. Isobutylmethylxanthine (IBMX) increased [³H] thymidine incorporation in control cultures, in the absence of cortisol, and increased the response to PGE₂ in control and cortisol-treated cultures. [³H] proline incorporation into collagen and noncollagen protein was measured in the continuous presence of prostaglandins and cortisol for 72–96 h (continuous model) or when prostaglandins and cortisol were applied for 24 h, followed by culture for 48 h in control medium (on/off model). The effects on collagen were greater than on noncollagen proteins, so that the percent of collagen synthesis increased. The effects of prostaglandins and forskolin paralleled their mitogenic effects. PMA increased only noncollagen protein. Indomethacin did not diminish the anabolic response, while aphidicolin produced only partial inhibition. We conclude that the anabolic effects of prostaglandins on replication and differentiation of osteoblasts are likely to be mediated by an EP-2 receptor that stimulates adenylate cyclase.