Interference of dichloromethane diphosphonate with parathyroid hormone effects at the bone but not at the kidney level.

Treatment with dichloromethane diphosphonate (Cl2MDP, 10 mg P/kg s.c. for 3 days) did not abolish the rapid hypocalciuric effect of acute administration of parathyroid hormone (PTH) to thyroparathyroidectomized (TPTX) rats. Cl2MDP impaired, however, the slower hypercalcemic response to PTH. This latter effect of Cl2MDP did not result from increased renal excretion of calcium. Thus, Cl2MDP does not interfere with the kidney but with the bone effect of PTH. This finding explains, at least in part, why, under treatment with Cl2MDP, there is still an effective regulation of plasma calcium.