Analysis of placental vascularization in a pharmacological rabbit model of IUGR induced by L-NAME, a nitric oxide synthase inhibitor.

Objectives: We have previously validated the use of L-nitro-arginine methyl ester (L-NAME), a nitric oxide synthase inhibitor, to induce placental hypoperfusion in a rabbit model. Here, the effects of L-NAME on placental vascularization were explored. Transplacental transfer of L-NAME and/or its active metabolite, NG-nitro-L-arginine (L-NOARG), was evaluated.

Methods: 25 pregnant female rabbits were allocated on day 24 to one of 5 groups: L-NAME groups (31.35, 62.5, 125 and 250 mg/kg/day) or Control group (C). On Day 28, the labyrinthine area was analyzed for stereology and gene expression. L-NAME and L-NOARG were quantified in maternal and fetal blood.

Results: The volume density of fetal vessels was significantly decreased in L-NAME (including 62.5-250 mg/kg/day which induced an IUGR) compared to C groups. L-NAME induced an increase of the volume and surface density of the maternal blood space. The trophoblast volume density remained unchanged as well as the surface density of fetal vessels. Relative expression of eNOS, VEGFA, VEGFR-1 and VEGFR-2 in placentas was not affected by 125 mg/kg/day L-NAME treatment, whereas IGF-2 expression was significantly increased in this L-NAME group compared to C. L-NAME was not detected in maternal nor fetal plasma. In contrast, fetal to maternal L-NOARG ratio was 100% in all L-NAME groups.

Conclusion: These data demonstrate that L-NAME induced placental hypovascularization. The active L-NOARG metabolite is found in maternal and fetal plasma at similar concentrations. This could impact the fetal growth and reduces the interest of this model to study fetal outcomes of placental hypoperfusion.