OS059. Blockade of the bradykinin B2 receptor in early pregnancy reduces fetal growth and trophoblast invasion in guinea-pigs

INTRODUCTION:Research in preeclampsia (PE) is hampered by the difficulty of sampling the placental bed in early pregnancies followed to delivery to be defined as normal or preeclamptic. Thus, animal models contribute to the understanding of its physiopathology. The guinea-pig shares with humans extensive vascular remodelling, a hemomonochorial placenta [1] and a vasodilator and angiogenic utero-placental repertoire [2]. In pregnancy it expresses bradykinin (BK) B1R and B2R receptors in cells related to invasion, angiogenesis and vasodilatation. In addition, in HTR-8/SVneo cells, BK induces a B2R-mediated increase in migration and invasion [3]. OBJECTIVES:To test whether blocking the B2R with a rodent-selective non-peptide antagonist Bradyzide (BDZ) from days 20 to 34 of an ≈65 day gestation - period of maximal trophoblast invasion and placental development - induces PE-like morphological and functional alterations. METHODS:Virgin Pirbright guinea-pigs (Cavia Porcellus) after mating and echographic confirmation of pregnancy, were allocated in gestational day 20 to to subcutaneous implantation of Alzet pumps that delivered for 14 days saline (Control; n=7), BDZ0,875mg/kg/day (BDZ0,87; n=6) and BDZ 1,2mg/kg/day (BDZ1,2; n=7). Systolic pressure was acquired in the right hindlimb with a Power Lab 8 SP and analyzed with Labchart at day 34. On that day dams were sacrificed, vesical urine was extracted for protein determination, the fetuses and corresponding placentas weighed and the cephalo-caudal length measured. The placentas were studied by HE and immunohistochemistry for cytokeratin to identify trophoblasts. Results are expressed as means±SE. Statistical analysis was performed with Graphpad Prism 5.1, using one-way ANOVA, the recommended post hoc tests and χ2 test. RESULTS:Maternal systolic pressure tended to increase in BDZ0,875 and BDZ1,2 versus controls (63±567±6 versus 56±2,mm Hg respectively; NS). Proteinuria was not observed in any group. The number of viable fetuses tended to be reduced in both BZD treated groups (NS). The fetal weight (% maternal weight) was reduced in animals treated with BDZ0,875 and BDZ1,2 (042±002 and 045±001 versus 054±0,04 in controls; p (P<0.01 and 0.05 respectively). The cephalo-caudal length was reduced in BDZ0,875 and BDZ1,2 (373±24 and 371±07 versus 422±21mm in controls; P<0.01). No differences were observed in placental weight. Spiral arteries surrounded by trophoblasts (%) were reduced in BDZ 0875 and BDZ1,2 versus controls (63 and 66.6 versus 100%, P=0.02). Invaded spiral arteries (%) were also reduced in the treated groups (80 and 43 versus 100%; P<0.002) No differences were observed in the depth of trophoblast decidual invasion. CONCLUSION:This study demonstrates that blocking the B2R in early pregnancy impairs fetal growth and transformation of the spiral arteries, and supports the role of the B2R in the local physiological adaptation. Further studies are needed to elucidate whether the early impairment translates to hypertension and proteinuria in the last third of pregnancy; if so, the guinea-pig would provide a model to understand the physiopathology of the syndrome. Study financed by Fondecyt 1080228.