Comparison of rat and human parathyroid hormone 2 (PTH2) receptor activation: PTH is a low potency partial agonist at the rat PTH2 receptor.

The human PTH2 receptor, expressed in tissue culture cells, is selectively activated by PTH. Detailed investigation of its anatomical and cellular distribution has been performed in the rat. It is expressed by neurons in a number of brain nuclei; by endocrine cells that include pancreatic islet somatostatin cells, thyroid parafollicular cells, and peptide secreting cells in the gastrointestinal tract; and by cells in the vasculature and heart. The physiological role of the PTH2 receptor expressed by these cells remains to be determined. All pharmacological studies performed to date have used the human receptor. We have now isolated a complementary DNA including the entire coding sequence of the rat PTH2 receptor and compared its pharmacological profile with that of the human PTH2 receptor when each is expressed in COS-7 cells. PTH-based peptides, including rat PTH(1-84), rat PTH(1-34), and human PTH(1-34), have low potency at the rat PTH2 receptor for stimulation of adenylyl cyclase (EC50 = 19-140 nM). When compared with the effect of a bovine hypothalamic extract, PTH-based peptides are partial agonists at the rat PTH2 receptor. This suggests that PTH is unlikely to be a physiologically important endogenous ligand for the PTH2 receptor. A peptide homologous to an activity detected in a bovine hypothalamic extract is a good candidate for the endogenous PTH2 receptor ligand.