Administration of angiotensin II and a bradykinin B2 receptor blocker in midpregnancy impairs gestational outcome in guinea pigs

Abstract

Background: The opposing renin-angiotensin system (RAS) and kallikrein-kinin system (KKS) are upregulated in pregnancy and localize in the utero-placental unit. To test their participation as counter-regulators, circulating angiotensin II (AII) was exogenously elevated and the bradykinin B2 receptor (B2R) was antagonized in pregnant guinea-pigs. We hypothesized that disrupting the RAS/KKS balance during the period of maximal trophoblast invasion and placental development would provoke increased blood pressure, defective trophoblast invasion and a preeclampsia-like syndrome.

Methods: Pregnant guinea-pigs received subcutaneous infusions of AII (200 μg/kg/day), the B2R antagonist Bradyzide (BDZ; 62.5 microg/kg/day), or both (AII + BDZ) from gestational day 20 to 34. Non-pregnant cycling animals were included in a control group (C NP) or received AII + BDZ (AII + BDZ NP) during 14 days. Systolic blood pressure was determined during cycle in C NP, and on the last day of infusion, and 6 and 26 days thereafter in the remaining groups. Twenty six days after the infusions blood and urine were extracted, fetuses, placentas and kidneys were weighed, and trophoblast invasion of spiral arteries was defined in the utero-placental units by immunocytochemistry.

Results: Systolic blood pressure transiently rose in a subgroup of the pregnant females while receiving AII + BDZ infusion, but not in AII + BDZ NP. Plasma creatinine was higher in AII- and BDZ-treated dams, but no proteinuria or hyperuricemia were observed. Kidney weight increased in AII + BDZ-treated pregnant and non-pregnant females. Aborted and dead fetuses were increased in dams that received AII and AII + BDZ. The fetal/placental weight ratio was reduced in litters of AII + BDZ-treated mothers. All groups that received interventions during pregnancy showed reduced replacement of endothelial cells by extravillous trophoblasts in lateral and myometrial spiral arteries.

Conclusions: The acute effects on fetal viability, and the persistently impaired renal/placental sufficiency and incomplete arterial remodeling implicate the RAS and KKS in the adaptations in pregnancy. The results partially confirm our hypothesis, as a preeclampsia-like syndrome was not induced. We demonstrate the feasibility of characterizing systemic and local modifications in pregnant guinea-pig, supporting its use to study normal placentation and related disorders.

Figure 1

Systolic blood pressure in pregnant and non-pregnant guinea-pigs treated with angiotensin II (AII), bradyzide (BDZ), or AII + BDZ. Systolic blood pressure on gestational days 34 (A) and 60 (B) in controls (C), AII, BDZ and AII + BDZ treated dams and in AII + BDZ-treated non-pregnant females (AII + BDZ NP). The broken line depicts the mean systolic blood pressure of 73.2 ± 7.5 SEM mm Hg in untreated non-pregnant females (C NP); continuous line represents mean values.

Figure 2

Fetal weight and fetal/placental weight ratios from dams treated with saline, angiotensin II (AII), Bradyzide (BDZ), or AII + BDZ. (A) Fetal weight. (B) Fetal/placental weight ratio. Continuous line represents mean values. *P < 0.05; †P < 0.01.

Figure 3

Intraluminal extravillous trophoblasts in spiral arteries on gestational day 60 in dams treated with saline, angiotensin II (AII), Bradyzide (BDZ), or AII + BDZ. (A) Lateral spiral artery endothelium replaced by extravillous trophoblasts (EVT) (% perimeter) in dams treated with saline, AII, BDZ, or AII + BDZ. (B) Myometrial spiral artery endothelium replaced by EVT (% perimeter) in dams treated with saline, AII, BDZ, or AII + BDZ. Continuous line represents mean values. **P < 0.005; ***P < 0.0005.

Figure 4

Representative sections of spiral arteries on day 60 of gestation in dams treated with saline (C), Bradyzide (BDZ), angiotensin II (AII) angiotensin II + Bradyzide (AII + BDZ). Endoluminal trophoblasts in lateral and myometrial spiral arteries are depicted in the upper and lower panel, respectively. The whole-mount haematoxylin/eosin section of the guinea-pig utero-placental interface includes in blue ovals the zones from which the microphotographs were acquired; trophoblasts were identified by anti-cytokeratin and highlighted by * and interrupted lines. Magnification x400 in upper panel and x100 in lower panel.