Delayed stimulatory effect of cyclic AMP on bone resorption in vitro

Abstract

Abstract. The effect of dibutyryl cyclic AMP (dbcAMP) and the phosphodiesterase inhibitors 3-isobutyl methylxanthine (IBMX) and theophylline on bone resorption was studied in an organ culture system for 96– 144 h using half calvaria from 6–7 day old mice. The magnitude of resorption was assessed by measuring the release from the bones of previously incorporated 45Ca. It was observed that dbcAMP, IBMX and theophylline, following a lag period or a period of reduced bone resorption, all progressively increased mineral mobilization. Although the continuous presence of dbcAMP increased mineral mobilization more than a temporary exposure, a limited treatment of 24 h with the nucleotide was sufficient to bring about the delayed stimulatory response. It is concluded that the observations support our earlier proposal that cAMP is not a mediator of the early stages of parathyroid hormone (PTH)- and prostaglandin E2 (PGE2)-stimulated bone resorption. We suggest that the role played by cAMP may be related to the capacity of PTH and PGE2 to develop new osteoclasts, a phenomenon which takes more than 24 h to be observed.