CYCLOOXYGENASE PRODUCTS DO NOT MODULATE ANGIOTENSIN-II INDUCED CONTRACTIONS OF HUMAN CHORIONIC PLATE ARTERIES

OBJECTIVE: This study sought to determine whether cyclooxygenase products modulate angiotensin II-induced contractions of human placental arteries. STUDY DESIGN: Ring segments of chorionic plate arteries (3 to 5 mm inner diameter) were obtained after normal vaginal deliveries. Active force in response to 10(-6) mol/L angiotensin II or 10(-4) mol/L arachidonic acid was measured in the presence or absence of 10(-6) mol/L indomethacin to inhibit cyclooxygenase. The response of K+ contracted arteries to the stable prostacyclin analog iloprost was also tested to determine whether prostacyclin relaxes these vessels. Statistical differences were assessed by analysis of variance, Wilcoxon sign rank test, or Student t test with Bonferroni correction for multiple comparisons. RESULTS: Successive applications of angiotensin II produced significantly less contraction than the original dose (angiotensin II tachyphylaxis). Angiotensin II tachyphylaxis was unaffected by indomethacin. Arachidonic acid caused an indomethacin-sensitive contraction and iloprost failed to relax the arteries. CONCLUSIONS: These results suggest that cyclooxygenase products do not mediate angiotensin II tachyphylaxis in these vessels.