In an additional experiment PTH and DBcAMP effects on serum 47 Ca activity were measured in PTX rats with prelabelled bone: DBcAMP did not cause a significant rise in serum 47 Ca as did PTH. ConcIusionsDBcAMP elevates serum Ca by increased intestinal Ca absorption. The amount of Ca being additionally absorbed after DBcAMP treatment was not utilized by deposition in bone, but excreted in the urine. DBcAMP did not alter serum Ca in starving rats. This and the absence of increased 47Ca remobilization from prelabelled bone by DBcAMP indicates that DBcAMP does not increase serum Ca by stimulating bone resorption. PTH increases bone resorption in PTX rats and intestinal Ca absorption in intact rats. The reduction of Ca Absorption by PTH in PTX rats remains unexplained and needs further investigation.

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