Effect of Ro 61-1790, a selective endothelin-A receptor antagonist, on systemic and uterine hemodynamics and fetal oxygenation in sheep

Endothelin and the regulation of uteroplacental perfusion in nitric oxide synthase inhibition-induced fetal growth restriction

The vasoactive mediators nitric oxide and endothelin are both produced in and active in the uterine and placental vasculature. Inhibition of nitric oxide synthase (NOS) results in fetal growth restriction. Endothelin (ET-1) is upregulated in the setting of NOS inhibition. Our purpose was to determine the impact of ET-1 on uterine and placental perfusion in the pregnant rat treated with a NOS inhibitor. Timed-pregnant Sprague-Dawley rats were treated with L-NAME (2.5 mg/kg/h), with and without A-127722 (10 mg/kg/day), or their respective vehicles, for 1, 4, or 7 days beginning on day 14 of gestation. Blood flow to various organs was determined by microsphere infusion. Maternal and fetal plasma nitrate/nitrite (NOx) was determined by fluorometric assay. Uterine and placental perfusion was significantly decreased by NOS inhibition and was restored to normal by ETA antagonism at 1 and 4 days of infusion but not at 7 days. Maternal plasma NOx, but not fetal plasma NOx, was significantly decreased by NOS inhibition alone. ETA antagonism in combination with NOS inhibition significantly lowered fetal plasma NOx. These results indicate that ET-1 is an important regulator of uterine and placental perfusion in the NOS inhibition model of fetal growth restriction. Our results also suggest that maternal administration of L-NAME does not result in significant transport of L-NAME across the placenta, but that addition of an ETA antagonist results in increased placental perfusion, allowing L-NAME greater access to the fetal compartment.

Effects of blockade of the endothelin receptor A and inhibition of nitric oxide synthesis on uteroplacental and renal blood flow in awake pregnant rats

OBJECTIVE

The aim of this study was to evaluate the role of the ETA receptor and nitric oxide (NO) in the regulation of uteroplacental and renal blood flow in pregnant rats.

STUDY DESIGN

Regional blood flows were measured by the microsphere technique in pregnant Sprague-Dawley rats (term 23 days). Blood flow was measured before and after ETA receptor blockade (BQ-123, 1 mg/kg) at gestational day (GD) 19 or 21 (n=8 and n=9, respectively). In 2 additional groups blood flow was measured before and after NO synthase inhibition (L-NAME 2 microg/min) at GD 19 or 21 (n=10 in each group).

RESULTS

BQ-123 significantly increased placental and myometrial blood flows by almost 80% and 35%, respectively, at both gestational ages. BQ-123 did not alter renal blood flow. No effect on placental or myometrial blood flow was observed after L-NAME infusion, neither at GD 19 nor GD 21. Renal blood flow decreased by nearly 35% in both groups after L-NAME.

CONCLUSION

There is an important role for endogenous ET in the regulation of uteroplacental blood flow in the rat. NO contributes to a significant vasodilatation in the renal vasculature; however, NO appears not to be involved in the maintenance of uteroplacental blood flow in the awake pregnant rat.