Inhibitory effect of [Tyr34]bPTH-(7-34)-amide on bPTH-(1-34) ability to reduce uterine contraction.

Synthetic bovine parathyroid hormone containing the 1-34 NH2-terminal amino acids [bPTH-(1-34)] inhibits uterine contraction stimulated by a variety of agonists. Previously, we reported that the parathyroid hormone analogue [Nle8, Nle18, Tyr34]bPTH-(3-34)amide [NTA-(3-34)] antagonized this effect of bPTH-(1-34) while the analogue [Tyr34]bPTH-(7-34)amide [bPTH-(7-34)] used in this study stimulated uterine contraction. However, contrary to this previous report, bPTH-(7-34) in the present study failed to initiate a contractile response and instead resulted in an inhibitory response to the bPTH-(1-34) effect on uterine contraction in a dose-related manner. The inhibitory response of bPTH-(7-34) was further confirmed by demonstrating that this preparation of bPTH-(7-34) was capable of blocking bPTH-(1-34)-stimulated adenylate cyclase activity on particulate fractions of osteoblast-like cells from neonatal mouse calvarial. These results are consistent with those in the literature for the antagonistic effect of the 7-34 PTH fragment.