PARATHYROID HORMONE-RELATED PEPTIDE (1 TO 34) INHIBITS IN-VITRO OXYTOCIN-STIMULATED ACTIVITY OF PREGNANT BABOON MYOMETRIUM

OBJECTIVES: We sought to determine the in vitro effect of parathyroid hormone-related protein fragment 1 to 34 on oxytocin precontracted myo metrium from baboons in late gestation and to explore possible regiona l uterine differences in responsiveness comparing muscle strips from t he lower uterine segment, posterior and anterior corpus, and fundus. S TUDY DESIGN: We used cumulative concentration response (1 to 100 nmol/ L) curves to parathyroid hormone-related protein (1 to 34) in isolated strips of baboon myometrium obtained at cesarean hysterectomy of 6 pr egnant baboons in the last third of pregnancy. RESULTS: Parathyroid ho rmone-related protein (100 nmol/L) decreased both amplitude and freque ncy of contraction. The maximum effect of parathyroid hormone-related protein on the amplitude of contractions was greater than saline solut ion (2-way analysis of variance, F ratio 424.0, P <.001), but there wa s no difference comparing the four regions of the uterus (F ratio 1.34 2, P =.286). The maximum effect of parathyroid hormone-related protein on the frequency of contractions was greater than saline solution (2- way analysis of variance, F ratio 162.5, P <.0001), but no difference in response was noted in the 4 regions of the uterus (F ratio = 0.682, P =.572). CONCLUSION: Parathyroid hormone-related protein completely inhibited the contractile effect of high doses of oxytocin in the lowe r segment, corpus, and fundus of the baboon uterus. No difference in r esponse of myometrium was obtained from different regions of the uteru s.