Abstract-Agonistic autoantibodies to the angiotensin II type I receptor (AT1-AA) and endothelin -1 (ET-1) are suggested to be important links between placental ischemia and hypertension during preeclampsia. Activation of the angiotensin II type 1 receptor (AT1R) increases endothelial cell production of ET-1; however, the importance of ET-1 in response to AT1-AA-mediated AT1 R activation during preeclampsia is unknown. Furthermore, the role of AT1-AA-mediated increases in blood pressure during pregnancy remains unclear. The objective of this study was to test the hypothesis that AT1-AA, increased to levels observed in preeclamptic women and placental ischemic rats, increases mean arterial pressure (MAP) by activation of the ET-1 system. Chronic infusion of purified rat AT1-AA into normal pregnant (NP) rats for 7 days increased AT1-AA from 0.68Ϯ0.5 to 10.88Ϯ1.1 chronotropic units (PϽ0.001). The increased AT1-AA increased MAP from 99Ϯ1 to 119Ϯ2 mm Hg (PϽ0.001). The hypertension was associated with significant increases in renal cortices (11-fold) and placental (4-fold) ET-1. To determine whether ET-1 mediates AT1-AA-induced hypertension, pregnant rats infused with AT1-AA and NP rats were treated with an ET A receptor antagonist. MAP was 100Ϯ1 mm Hg in AT1-AAϩET A antagonist-treated rats versus 98Ϯ2 mm Hg in ET A antagonist-treated rats. Collectively, these data support the hypothesis that one potential pathway whereby AT1-AAs increase blood pressure during pregnancy is by an ET-1-dependent mechanism. Key Words: preeclampsia Ⅲ hypertension Ⅲ kidney Ⅲ placenta Ⅲ inflammation T he initiating event in early onset preeclampsia is postulated to involve inadequate vascularization of the subplacental decidua with reduced placental perfusion that leads to hypertension during pregnancy by mechanisms not yet elucidated. 1,2 Recent studies have suggested that the production of agonistic autoantibodies to the angiotensin II (Ang II) type I receptor (AT1-AA) may be an important link between placental ischemia and hypertension in preeclamptic women. 3-8 The AT1-AA induces signaling in vascular cells that are blocked by an AT1 receptor antagonist including activating protein-1, calcineurin, and nuclear factor kappa B activation. 3,4,7 Recent studies by Zhou et al demonstrate that immunoglobulin isolated from preeclamptic women increases systolic blood pressure 4 days after retro-orbital injection into pregnant mice. 7,8 This hypertensive response was attenuated by administration of an AT1 receptor antagonist. Although these findings suggest that AT1-AAs from preeclamptic women increases blood pressure in pregnant mice, possibly by activation of the AT1 receptor, it remains unclear by what mechanism purified AT1-AA mediates hypertension during pregnancy.We recently reported that hypertension in response to reductions in uterine perfusion pressure in pregnant rats (RUPP) is associated with increased circulating levels of the AT1-AA. 9,10 Moreover, we found that the increased blood pressure response in RUPP pregnant rats decreased ma...

BACKGROUND Preeclampsia is considered a disease of immunological origin associated with abnormalities in inflammatory cytokines, tumor necrosis factor-α (TNF-α), and activated lymphocytes secreting AT1-AA. Recent studies have also demonstrated that an imbalance of angiogenic factors, soluble fms-like tyrosine kinase (sFlt-1), and sEndoglin, exists in preeclampsia; however, the mechanisms that initiate their overproduction are unclear. METHODS To determine the role of immune regulation of these factors, circulating and placental sFlt-1 and/or sEndoglin was examined from pregnant rats chronically treated with TNF-α or AT1-AA. On day 19 of gestation blood pressure was analyzed and serum and tissues were collected. Placental villous explants were excised and cultured on matrigel coated inserts for 24 h and sFlt-1 and sEndoglin was measured from media. RESULTS In response to TNF-α-induced hypertension, sFlt-1 increased from 180 ± 5 to 2,907 ± 412 pg/ml. sFlt-1 was also increased from cultured placental explants of TNF-α induced hypertensive pregnant rats (n = 12) (2,544 ± 1,132 pg/ml) vs. explants from normal pregnant (NP) rats (n = 12) (2,189 ± 586 pg/ml) where as sEng was undetectable. Circulating sFlt-1 increased from 245 ± 38 to 3,920 ± 798 pg/ml in response to AT1-AA induced hypertension. sFlt-1 levels were higher (3,400 ± 350 vs. 2,480 ± 900 pg/ml) in placental explants from AT1-AA infused rats (n = 12) than NP rats (n = 7). In addition, sEndoglin increased from 30 ± 2.7 to 44 ± 3.3 pg/ml (P < 0.047) in AT1-AA infused rats but was undetectable in the media of the placental explants. CONCLUSIONS These data suggest that immune factors may serve as an important stimulus for both sFlt-1 and sEndoglin production in response to placental ischemia.

This study indicates that AT1-AA's contribute to placental oxidative stress; one mechanism whereby the AT1-AA mediates hypertension during pregnancy.

Although abnormal soluble fms-like tyrosine kinase-1 (sFlt-1) production is thought to be an important factor in the pathogenesis of preeclampsia (PE), the mechanisms that regulate the production of sFlt-1 during PE are unclear. While our laboratory has shown tumor necrosis factor-α (TNF-α) and sFlt-1 to be elevated in pregnant rats in response to placental ischemia, the importance of TNF-α in the regulation of sFlt-1 production is unknown. Therefore, the purpose of this study was to determine the role of TNF-α in mediating the increase in sFlt-1 in response to placental ischemia or hypoxia. Reductions in uterine perfusion pressure in pregnant rats significantly increased plasma levels of sFlt-1 and tended to increase TNF-α, an effect markedly attenuated by pretreatment with a TNF-α inhibitor etanercept (0.4 mg/kg). To further assess chronic interactions between TNF-α and sFlt-1, we examined a chronic effect of TNF-α infusion (50 ng/day) into normal pregnant rats to increase plasma sFlt-1 levels, as well as the effects of acute hypoxia on placental sFlt-1 production in the absence and presence of TNF-α blockade. Placental explants exposed to hypoxic conditions had enhanced TNF-α levels versus normoxic conditions, as well as increased sFlt-1 production. Pretreatment of placental explants with etanercept (15 μM) significantly reduced TNF-α levels in response to hypoxia but did not attenuate sFlt-1 production. These data suggest that while TNF-α may not play an important role in stimulating sFlt-1 production in response to acute hypoxia, a more chronic hypoxia, or placental ischemia may be an important stimulus for enhanced sFlt-l production.

Preeclampsia, (PE) new onset hypertension with proteinuria during pregnancy, is associated with increased reactive oxygen species, the vasoactive peptide ET-1, T and B lymphocytes, soluble antiangiogenic factors sFlt-1 and sEndoglin (sFlt-1 and sEng) and agonistic autoantibodies to the angiotensin II type I receptor (AT1-AA). One important area of investigation for our laboratory has been to determine what role AT1-AA play in the pathophysiology associated with PE. To achieve this goal we examined the effect of AT1-AA suppression on hypertension in response to placental ischemia as well as the effect of AT1-AA to increase blood pressure, ET-1, ROS, and sFlt-1 in normal pregnant rats (NP). We have demonstrated reductions in uterine perfusion pressure (RUPP) to be a stimulus for AT1-AA during pregnancy. We utilized the technique of B cell depletion to suppress circulating AT1-AA in RUPP rats and found that AT1-AA suppression in RUPP rats was associated with lower blood pressure and ET-1 activation. To determine a role for AT1-AA to mediate hypertension during pregnancy we have chronically infused purified rat AT1-AA (1:50) into NP rats and analyzed blood pressure and soluble factors. We have consistently shown that AT1-AA infused rats significantly increased AT1-AA and blood pressure above NP rats. This hypertension is associated with significantly increased ET-1 in renal cortices (11-fold) and placenta (4-fold), and approximately 2 to 3 fold increase in placental oxidative stress. Furthermore, antiangiogenic factors sFlt-1 and sEng were significantly increased in AT1-AA induced hypertensive group compared to the NP controls. Collectively, these data indicate an important role for AT1-AA stimulated in response to placental ischemia to cause hypertension during pregnancy.