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 myometrium from baboons in late gestation and to explore possible regional uterine differences in responsiveness comparing muscle strips from the lower uterine segment, posterior and anterior corpus, and fundus. STUDY 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 pregnant baboons in the last third of pregnancy. RESULTS: Parathyroid hormone-related protein (100 nmol/L) decreased both amplitude and frequency of contraction. The maximum effect of parathyroid hormone-related protein on the amplitude of contractions was greater than saline solution (2-way analysis of variance, F ratio 424.0, P < .001), but there was no difference comparing the four regions of the uterus (F ratio 1.342, 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 lower segment, corpus, and fundus of the baboon uterus. No difference in response of myometrium was obtained from different regions of the uterus.