THE ROLE OF ENDOTHELIUM IN PHENYLEPHRINE-INDUCED AND POTASSIUM-INDUCED CONTRACTIONS OF THE RAT AORTA DURING PREGNANCY

The involvement of endothelium in the contractile responses of rat aor tic rings to phenylephrine and potassium chloride in pregnancy was exa mined. Contractions in response to both agents were significantly grea ter in rings from non-pregnant rats than in rings from pregnant rats, and they were unaltered by treatment of the rings with indomethacin. D e-endothelialization potentiated the contractions of rings from pregna nt rats in response to phenylephrine, but had no significant effect on similar rings contracted with potassium chloride. Whereas de-endothel ialization had no significant effect on the contractions to phenylephr ine in rings from non-pregnant rats, it decreased those of rings from the same type of rats, contracted with potassium chloride. Pregnancy s ignificantly inhibited contractions in response to calcium chloride of rings treated with phenylephrine or potassium chloride. The effect of endothelium removal on contractions to calcium chloride in rings from pregnant and non-pregnant rats treated with phenylephrine or potassiu m chloride was similar to that observed for phenylephrine-induced and potassium chloride-induced contractions, respectively. Contractions of intact aortic rings from pregnant and non-pregnant rats to phenylephr ine in calcium-free medium were similar, Results of the study suggest that the effect of pregnancy on the contractions of the rat aorta in r esponse to phenylephrine and potassium chloride is at least partly med iated by the endothelium and is independent of prostaglandin synthesis . The endothelial factor involved in this effect appears to modulate c ontractions by interfering with calcium influx through the receptor-op erated calcium channels and the voltage-operated calcium channels.