Effects of different vasopressors on the contraction of the superior mesenteric artery and uterine artery in rats during late pregnancy

Background: ：Hypotension after neuraxial anaesthesia is one of the most common complications during caesarean section. Vasopressors are generally agreed to be the most effective way to improve hypotension, but it is unclear which of these drugs is best for caesarean section. We assessed the effects of vasopressors on the contractile response of uterine arteries and superior mesenteric arteries in pregnant rats, with the goal of identifying a drug that raises the blood pressure of the systemic circulation while minimally affecting the uterine and placental circulation. Methods： Isolated ring segments from the uterine and superior mesenteric arteries of pregnant rats were mounted in organ baths, and their contractile responses to several vasopressor agents were studied. Concentration-response curves for norepinephrine, phenylephrine, metaraminol and vasopressin were constructed. Results：The experimental results showed that the contractile response of the mesenteric artery to norepinephrine, as measured by the pEC50 of the drug, was stronger than that of the uterine artery (5.617 ± 0.11 vs. 4.493 ± 1.35, p=0.009), and the contractile response of the uterine artery to metaraminol was stronger than that of the mesenteric artery (pEC50: 5.084±0.17 vs 4.92±0.10, p=0.007). There was no statistically significant difference in the pEC50 of phenylephrine or vasopressin between the two blood vessels. Conclusion： In vitro experiments show that compared with phenylephrine, metaraminol , vasopressin, norepinephrine can contract peripheral blood vessel more strongly, while having the least effect on the contraction of uterine artery. These findings provide some support for the use of norepinephrine in mothers between the time of neuraxial anaesthesia and the delivery of the foetus.