Original Article The Effects of Extracellular Calcium-Sensing Receptor Ligands on the Contractility of Pregnant

Ligands for extracellular calcium-sensing (CaS) receptors inhibit oxytocin-induced contractions of the rat’s uterus. In this study, we investigated whether the CaS receptor ligands calindol, cinacalcet, and calhex 231 have similar effects on pregnant human myo-metrium. We compared their effects to those of the calcium-channel blocker nifedipine. In conventional concentration–effect experiments, both the mean contractile force (MCF) and the maximum amplitude of contractions induced by 1 nmol/L oxytocin were inhibited by nifedipine. Calindol and cinacalcet were ineffective as inhibitors, while calhex-231 produced partial inhibition. When single 10 mmol/L doses were applied calhex-231 produced a slowly developing inhibition, reducing the MCF to 38%, and amplitude to 34%, of vehicle controls after 1 hour. In similar experiments, calindol was ineffective while cinacalcet weakly inhibited only the amplitude. Immunohistochemistry revealed sparse expression of CaS receptors in pregnant human myometrium