Effects of bone in vitro of bovine parathyroid hormone and synthetic fragments representing residues 1-34, 2-34 and 3-34.

The biological activities of bovine parathyroid hormone (BPTH) and fragments comprising portions of its amino-terminal sequence have been compared in three different assay systems using embryonic rat bone in vitro. Whereas the 3-34 fragment was without significant activity the 1-34 fragment caused all the actions characteristic of BPTH 1-84, extending to bone previous evidence that the amino-terminal residues are sufficient for expression of the biological effects of intact parathyroid hormone. However, the relative potencies of the fragment and the intact hormone were different in the various systems. BPTH 1-34 showed relatively low osteolytic activity and induced anabolic effects in both osteoblasts and cartilage cells of cultivated embryonic mouse radii which were not evoked by the intact hormone. Further work is required to determine the mechanisms responsible for these interesting alterations in relative potency of fragment and native hormone.