Protein deficiency suppresses bone resorption in sheep based on a short-term in vivo bone model

Six sheep were fed protein-deficient and control diets for 40 d for each diet in a crossover design. Each sheep was intramuscularly injected with 120 pmol.d-1.kg body wt-1 of 1,25-dihydroxycholecalciferol during the last 7 d of each dietary period. Approximately 100 mg of bone powder was implanted on the abdominal muscle on d 21 and d 28 of each dietary period. Plaques induced by the bone powder were harvested 12 d after the implantation. Tartrate-resistant acid phosphatase (TR-ACP) activity was lower and the number of multinucleated cells was smaller in plaques of animals during the protein-deficient period than during the control period. The administration of 1,25-dihydroxycholecalciferol increased the activity of TR-ACP and the number of multinucleated cells during both dietary treatments. However, TR-ACP activity was still lower and the cell number was still smaller during the protein-deficient period than during the control period when they were injected with 1,25-dihydroxycholecalciferol. These results suggest that protein deficiency reduces the activity of osteoclastic cell induction. The suppressive effect of protein deficiency on the induction and the activity of osteoclastic cells is not related to the action of 1,25-dihydroxycholecalciferol.