It has been recently hypothesized that in PIH a placental oxidant-antioxidant imbalance might cause the release of lipoperoxidation products into the circulation, with subsequent damage of endothelial cell membranes. In this hypothesis the endothelial cell and further increase in circulating lipoperoxide levels, which are by themselves able to induce smooth muscle constriction and increased pressor responsiveness to angiotensin II. In order to investigate this issue, we studied the basal content of lipid peroxides in terms of malondialdehyde (MDA) in the syncytiotrophoblast plasma membranes (SPM) from PIH women. Moreover, we investigated the susceptibility to peroxidation of SPM using an in vitro oxidative stress as a tool to verify the predisposition to the in vivo development of peroxidation products. The fatty acid composition of the membranes was also analyzed. Microvillus membrane lipoperoxide concentrations were significantly increased in PIH women (62.8 +/- 7.6 ng MDA/mg prot) compared with healthy pregnant subjects (37.6 +/- 4.8 ng MDA/mg prot; p < 0.01). The formation of TBARS under the action of phenylhydrazine was significantly greater in PIH women (90.3 +/- 7.4 mmol MDA/mol cholesterol) than in normal pregnant subjects (68.6 +/- 6.4 mmol MDA/mol cholesterol; p < 0.01). In PIH microvillus membrane we also observed a significant increase of the content of polyunsaturated arachidonic acid. The increased susceptibility to oxidative stress of SPMs from PIH women might be due either to reduced antioxidant systems or to an abnormality of the lipid composition of the membrane.(ABSTRACT TRUNCATED AT 250 WORDS)