We have previously reported that prostaglandin F(2alpha) (PGF(2alpha)) stimulates interleukin-6 (IL-6), a potent bone resorptive agent, through p44/p42 mitogen-activated protein (MAP) kinase in osteoblast-like MC3T3-E1 cells. In the present study, we investigated whether Rho-kinase is implicated in the PGF(2alpha)-stimulated IL-6 synthesis in MC3T3-E1 cells. PGF(2alpha) time-dependently induced the phosphorylation of myosin phosphatase targeting subunit (MYPT-1), a Rho-kinase substrate. Y27632, a specific Rho-kinase inhibitor, significantly reduced the PGF(2alpha)-stimulated IL-6 synthesis as well as the MYPT-1 phosphorylation. Fasudil, another inhibitor of Rho-kinase, suppressed the PGF(2alpha)-stimulated IL-6 synthesis. Y27632 and fasudil failed to affect the PGF(2alpha)-induced phosphorylation of p44/p42 MAP kinase. SB203580 and BIRB0796, potent inhibitors of p38 MAP kinase, suppressed the IL-6 synthesis induced by PGF(2alpha). While SP600125, an inhibitor of stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK), failed to reduce the synthesis. Y27632 as well as fasudil attenuated the PGF(2alpha)-induced phosphorylation of p38 MAP kinase. These results strongly suggest that Rho-kinase regulates PGF(2alpha)-stimulated IL-6 synthesis via p38 MAP kinase activation in osteoblasts.