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In the present study, treatment of IBMX, a phosphodiesterase (PDE) inhibitor, alone induced osteoclast formation in co-cultures of mouse bone marrow cells and calvarial osteoblasts. However, treatment of IBMX in combination with prostaglandin E₂(PGE₂) inhibited osteoclast formation in a dose-dependent manner. Among various isozyme-specific PDE inhibitors, a PDE4 specific inhibitor rolipram, showed similar effects as IBMX on osteoclast formation. To address the involvement of cyclic adenosine monophosphate (cAMP) in osteoclast formation, cAMP concentration in calvarial osteo- blasts was investigated. When calvarial osteoblasts were co-cultured with IBMX alone or in combination with PGE₂, the patterns of cAMP concentration in calvarial osteoblasts were differ each other, suggesting that cAMP in calvarial osteoblasts subtly regulates osteoclast formation.
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