OBJECTIVE: To test electric field stimulation on human placental vessels. METHODS: The effects of electric field stimulation on placental vessels were examined in an isometric myograph. RESULTS: Electric field stimulation induced contractions in human placental blood vessels in vitro under isometric conditions when bubbling carbogen through the organ bath. After reaching half-maximal contractions, the vessel rings showed spontaneous relaxation. Pretreatment with verapamil (10-6 mol/L) or nickel (Ni2+) (2 mmol/L) inhibited the contractions to a magnitude of 63.81% ± 7.69% and 88.36% ± 12.17% (mean ± standard error of the mean), respectively. In calcium (Ca2+)-free medium after combined cyclopiazonic acid (10-5 mol/L) and Ni2+ treatment, it was not possible to elicit contractions with electric field stimulation. Bubbling through physiologic in utero hypoxic gases enhanced the contractile responses of the human placental vessel rings to electric field stimulation. The spontaneous relaxation of the veins was not altered, but those of the arteries were reduced to zero. Testing the same gases on mesenteric arteries of rats had an opposite effect concerning contractility. Sodium nitrite decreased the contractions of the placental vessel rings, but the efficacy was decreased by the in utero gases. CONCLUSION: Electric field stimulation has a direct, non-neurogenic contractile effect on isolated placental vessels, which mainly depends on the influx of extracellular Ca2+ and on a mechanism independent of intracellular Ca2+ concentration elevation. Physiologic hypoxia has a stimulatory effect on the contractility of human placental vessels, therefore in utero gases should be used instead of carbogen gas; and electric field stimulation is a suitable method for the investigation of the direct effects of pharmacologic agents on human placental vessels.
ASJC Scopus subject areas
- Obstetrics and Gynaecology