Relative biologic activities of human and bovine parathyroid hormones and their synthetic, NH2-terminal (1-34) peptides, as evaluated in vitro with renal cortical adenylate cyclase obtained from three different species.

The relative biologic activities of native human parathyroid hormone, hPTH (1-84), native bovine parathyroid hormone, bPTH (1-84), and their respective synthetic, NH2-terminal, biologically-active (1-34) fragments were compared in vitro using adenylate cyclase preparations from human, chicken, and rat renal cortex. The concentrations of the hormones required for half-maximal stimulation of the enzymes were determined from dose response curves. bPTH (1-84) had greater apparent activity than hPTH (1-84), using rat or chicken renal adenylate cyclase, but, with human renal adenylate cyclase, the apparent activities of the two hormones were equal. Synthetic hPTH (1-34) possessed about 1/10 of the apparent activity of hPTH (1-84) in all three adenylate cyclase systems. However, (GLU22)bPTH (1-34) was about equal inapparent activity to bPTH (1-84) in the three systems. We propose that different rates of hormone degradation at or near renal receptor sites may be responsible for the dependence of the relative biologic activity on the assay system used. In the case of hPTH a peptide chain longer than (1-34) may be required for the full biologic activity of the hormone...