Carbonic anhydrase activity in fetal rat bone resorbing cells: inhibition by acetazolamide infusion

Skeletal growth during late fetal development is characterized by intense formation and resorption of the cartilage and bone matrix. In this study, we have evaluated the possible role played by carbonic anhydrase during fetal bone resorption in vivo. Pregnant rats were infused continuously from days 14 to 21 of gestation with acetazolamide a specific inhibitor of carbonic anhydrase, using an osmotic minipump. Carbonic anhydrase activity in long bones of 21 days old fetuses was determined by a previously validated histochemical staining method. In vivo infusion of acetazolamide induced a dose-dependent decrease in the number of carbonic anhydrase-positive resorbing cells whereas the total number of resorbing cells was not affected. At the low dose of 8 mg/day per kg, the number of chondroclasts and osteoclasts was decreased by 14.2 and 12.3% respectively (P less than 0.001) whereas serum calcium and phosphate remained unchanged in mothers and fetuses. At the dose of 40 mg/day per kg, acetazolamide reduced further the number of carbonic anhydrase positive-chondroclasts and osteoclasts by 28.8 and 27.5%, respectively (P less than 0.001), and induced a significant fall in serum calcium and phosphorus in fetuses. This study shows that an in vivo 28% inhibition of carbonic anhydrase activity in resorbing cells lowers serum calcium and indicates that the enzyme plays a significant role in bone resorption during normal fetal long bone growth.