We investigated adenylate cyclase distribution in 6-day- and 3-week-old calvariae and in 6-day-old long bone metaphyses from chickens. Reaction product distribution was on the plasma membrane of osteoblasts, pre-osteoblasts, and forming osteocytes which contacted one another. Osteoclasts and mature osteocytes lacked reaction product. Six-day calvariae reacted less intensively than the other two tissues. In controls, reaction product was markedly diminished or eliminated by removal of forskolin or substrates, or by addition of the inhibitor 2',5'-dideoxyadenosine. The results indicate the importance of cyclic AMP in osteoblast regulation. Osteocytes and osteoclasts may involve alternate mechanisms as major regularory systems.
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