Osteoblast numbers after calcitonin therapy: A retrospective study of paired biopsies obtained during long-term calcitonin therapy in postmenopausal osteoporosis

The present study is a retrospective examination of osteoblast indices in h uman iliac crest bone biopsies from a study on the long-term efficacy of ca lcitonin. Paired baseline and 2-year biopsies were examined from eight cont rol subjects and 10 treated subjects; treated subjects received 100 MRC uni ts synthetic salmon calcitonin (Calcimar, Armour Pharmaceutical Co, Scottsd ale, AZ) injected i.m. sub Q at bedtime. Control patients did not receive a placebo injection. All subjects received 400 units vitamin D-2 p.o. q.d, a nd 1200 mg CaCO3 p.o. q.d. When the differences in baseline and 2-year valu es were analyzed, subjects receiving calcitonin showed no decrease compared with control subjects for the fraction of osteoid surface lined by osteobl asts (ObS/OS) (but were in fact significantly greater, P = 0.04). There was no difference from control subjects in the number of osteoblasts/mm bone s urface (NOb/BPm), or mean mineral apposition rate (MAR). Since calcitonin i s receiving renewed interest for osteoporosis therapy, these data (derived from paired human biopsies) are valuable since they show that no decrease i n osteoblast cell number resulted from long-term calcitonin therapy. Result s point to the need for renewed investigation concerning the effect of calc itonin on osteoblast-osteoclast interactions.