Effect of parathyroid hormone–related peptide on human and rat myometrial contractility in vitro

Objectives: The aims of this study were primarily to investigate the effects of parathyroid hormone–related peptide (human fragment 1-34) on human nonpregnant and pregnant (nonlabor and labor) myometrial contractility in vitro and secondarily to compare these effects with those of parathyroid hormone–related peptide on rat myometrial contractility. Study Design: Isometric tension recording was performed under physiologic conditions in isolated myometrial strips obtained at hysterectomy and cesarean delivery and from Sprague-Dawley rats. The effect of cumulative additions of parathyroid hormone–related peptide (1, 10, and 100 nmol/L) on myometrial contractility was measured and the significance of results was assessed by 2-way analysis of variance. Results: Parathyroid hormone–related peptide exerted a statistically significant net relaxant effect on myometrial contractility in human nonpregnant myometrium (34.71%; P< .01), in human pregnant myometrium obtained before (18.27%; P< .05) but not after (10.32%; P> .05) the onset of labor, and in rat tissue (31.60%; P< .01). Conclusions: Parathyroid hormone–related peptide exerts a relaxant effect on human and rat myometrial tissue. In human myometrium, sensitivity to parathyroid hormone–related peptide is reduced in pregnancy and abolished by the onset of labor. (Am J Obstet Gynecol 2001;184:625-9.)