Sodium supplementation given for 1 week to nonpregnant rats induces changes that are adequate to maintain renal and circulatory homeostasis as well as arterial blood pressure. However, in pregnant rats, proteinuria, fetal growth restriction and placental oxidative stress are observed. Moreover, the decrease in blood pressure and expansion of circulatory volume, normally associated with pregnancy, are prevented by high-sodium intake. We hypothesized that, in these pregnant rats, a loss of the balance between pro-oxidation and antioxidation, particularly in kidneys and heart, disturbs the normal course of pregnancy and leads to manifestations such as gestational hypertension. We thus investigated the presence of oxidative/nitrosative stress in heart and kidneys following high-sodium intake in pregnant rats. Markers of this stress [8-Isoprostaglandin F₂ alpha, (8-iso-PGF₂) and nitrotyrosine], producer of nitric oxide [nitric oxide synthases (NOSs)], and antioxidants [superoxide dismutase (SOD) and catalase] were measured. Then, molecules (Na⁺,K⁺-ATPase and aconitase) or process (apoptosis [Bax and Bcl-2], inflammation [monocyte chemoattractant protein-1 (MCP-1), connective tissue growth factor (CTGF) and tumor necrosis factor alpha (TNF-)]) susceptible to free radicals were determined. In kidneys from pregnant rats on 1.8% NaCl-water, NOSs, apoptotic index and nitrotyrosine expression were increased whereas Na⁺,K⁺-ATPase mRNA and activity were decreased. In the left cardiac ventricle of these rats, heightened nitrotyrosine, 8-iso-PGF₂ and catalase activity together with reduced eNOS protein expression, and SOD and aconitase activities were observed. These findings suggest that oxidative/nitrosative stress in kidney and left cardiac ventricle destabilizes the normal course of pregnancy and could lead to gestational hypertension.