Osteoclast‐like cell formation in fetal and newborn long‐term baboon marrow cultures is more sensitive to 1,25‐dihydroxyvitamin D₃ than adult long‐term marrow cultures

It is unknown if osteoclasts derived from animals at different developmental stages differ. To study this question, we used a long‐term baboon marrow culture system in which osteoclast‐like multinucleated cells (MNC) are formed. Fetal, newborn, or adult baboon marrow cultures were tested to determine if they differ in their responsiveness to osteotropic hormones. In fetal and newborn marrow cultures 1,25‐dihydroxyvitamin D₃ (1,25D₃) at 10⁻¹⁰ M significantly increased MNC formation with a maximal effect seen at 10⁻⁹ M. Higher concentrations of 1,25D₃ progressively decreased MNC formation. In contrast, in adult baboon marrow cultures, 10⁻⁹ M 1,25D₃ was required to significantly increase MNC formation, with a maximal affect at 10⁻⁸ M 1,25D₃. Calcitonin (25–200 ng/ml) inhibited MNC formation in fetal, newborn, or adult baboon marrow cultures treated with 1,25D₃ in an identical manner. The effects of 1,25D₃ on granulocyte‐macrophage progenitor cells (CFU‐GM), the probable precursors of MNC, were identical in fetal and adult baboon marrow cultures, with a significant inhibition of CFU‐GM colony formation at 10⁻⁸ M 1,25D₃. These results suggest that 1) osteoclast precursors are more sensitive to some osteotropic hormones during the fetal and newborn periods, and 2) differences in the 1,25D₃ sensitivity of osteoclast‐like MNC formation in fetal, newborn, and adult baboon marrow cultures are not due to effects on early proliferating precursors but may result from effects of 1,25D₃ on fusion of later precursors for MNC.