5-Hydroxytryptamine and Thromboxane A2 as Physiologic Mediators of Human Umbilical Artery Closure

Abstract

Objective: This study investigated the response of the human umbilical artery to various agonists in order to determine which agents might be involved in umbilical cord closure.

Methods: Umbilical artery rings from 22 cesarean deliveries were suspended in tissue baths containing Krebs-Henseleit solution under low and normal oxygen conditions. Samples were challenged with 5-hydroxytryptamine, acetylcholine, angiotensin II, bradykinin, endothelin-1, histamine, norepinephrine, phenylephrine, and U46619 (a thromboxane A₂ mimetic).

Results: Only 5-hydroxytryptamine, bradykinin, endothelin-1, histamine, and U46619 produced appreciable maximal contractions. Furthermore, although the contractile force generated by these agonists was diminished in normal oxygen conditions, this reduction affected responses to 5-hydroxytryptamine and U46619 least.

Conclusion: 5-Hydroxytryptamine and U46619 demonstrated the characteristics most likely to be associated with closure of the umbilical artery, ie, they elicited strong, sustained contractions at physiologic concentrations and under both normal and low-oxygen conditions. These data suggest that closure of the umbilical artery may be mediated by 5-hydroxytryptamine and thromboxane A₂.