Effects of the administration of corticosterone, parathyroid hormone, or both, and of their withdrawal, on rat bone and cartilage histomorphometric parameters, and on osteoprotegerin and RANKL mRNA expression and proteins.

We have studied the effects of the treatment with corticosterone (CORT), parathyroid hormone (PTH), or both (CORT + PTH), and of their withdrawal (CORT-rec and CORT + PTH-rec), on the osteoprotegerin (OPG) and receptor activator of nuclear factor-kB ligand (RANKL) localization and expression and on histomorphometric parameters in primary and secondary spongiosa of rat femur and tibia metaphyses. In the secondary spongiosa of the CORT group, the bone remodeling and the OPG/RANKL mRNA ratio decreased. In the PTH group, the bone turnover and the structural and connectivity indices increased, and the OPG/RANKL mRNA ratio fell; this ratio rose, however, in the primary spongiosa. In the CORT + PTH group, remodeling values intermediate between those of the CORT and PTH groups, were detected in the secondary spongiosa, where OPG and RANKL mRNA rose. Return towards control values was found in the recovery groups. The Cartilage Growth Plate Width was reduced in the CORT and CORT + PTH groups and returned to normal values in the recovery groups, while it was not affected by PTH. Independently of treatments, both OPG and RANKL mRNA and proteins were co-localized in the same cartilage and bone cells and in several bone marrow cells. In conclusion, the catabolic effects induced by CORT treatment occur together with an OPG fall and a RANKL rise. In the PTH group in which the bone turnover increase, the OPG and RANKL mRNA expressions differ in the primary and secondary spongiosa, confirming that the bone tissue in these sites can have different metabolic trends.