The nutritional demand of tumour cells is extremely high  and may produce metabolic alterations that can compromise the availability of amino acids and other nutrients to foetal tissues . Ascitic fluid contains many factors capable of causing oedema and haemorrhage in the placenta of pregnant rats  and of decreasing the placental glycogen stores in tumour-bearing rats .
An optimal maternal-foetal exchange is necessary for a successful pregnancy. Complications associated with pregnancy, including limited intrauterine growth and pre-eclampsia, have been related to poor trophoblast invasion and/or placental insufficiency that may result in placental ischemia and oxidative stress . However, the mechanisms by which placental oxidative stress triggers the characteristic placental endothelial dysfunction responsible for the development of pre-eclampsia are not well understood . Placental anti-oxidative mechanisms play an important role during pregnancy, as shown by the elevated activities of GSH, GST isoenzymes and GST and GPX . Cervello et al.  studied pregnant rats treated with benzo(a)pyrene and reported an increase in the anti-oxidative capacity, seen as enhanced GST activity in the placental tissue of these rats compared to non-treated animals. However, these authors concluded that the increase in GST activity was insufficient to protect the foetus and that benzo(a)pyrene significantly increased the number of resorptions and reduced the foetal weight .
As shown here, there was a marked reduction in the GST activity of placental tissue in groups W and A. Assuming that tumour growth during pregnancy induces foetal resorption and death  and jeopardises the placental tissue by causing placental oedema  and a reduction in the level of placental glycogen , the changes in placental GST activity seen here could have an antioxidant function and may occur in parallel with programmed cell death. In late gestation in humans, there is increased oxidative stress in pregnancies complicated by diabetes, intrauterine growth retardation (IUGR) and preeclampsia, as well as increased trophoblast apoptosis and deportation, and altered placental vascular reactivity .
Tumour growth clearly damaged the placental tissue by altering the foetal/placental ratio and the levels of apoptotic signalling molecules such as cleaved PARP, cytochrome-c and caspase 3. Tumours can damage foetuses (high foetal resorption, foetal death or a decrease in foetal growth) through competition for nutrients and by harming the foetus and placenta indirectly through substances synthesized by the tumour and/or host cells present in ascitic fluid . Apoptosis occurs during normal development in different organs and tissues and is a normal phenomenon in trophoblast turnover, with no inflammatory response in the mother. Apoptosis is important for an appropriate balance in cell turnover, with the early, reversible stages of the apoptotic cascade being involved in the differentiation and fusion of the cytotrophoblast in animal models of pregnancy [39–42].
Normal placental development depends upon the differentiation and invasion of the trophoblast, the main cellular component of the placenta. Apoptosis in the trophoblast increases in normal placentas as gestation proceeds, with a higher incidence in pregnancies complicated by preeclampsia or IUGR . Apoptosis is triggered by different cell-type-specific signals that involve mitochondrial and receptor-mediated pathways and results in activation of the caspase cascade. At least two major mechanisms by which a caspase cascade may be initiated have been suggested: one involves death receptors that activate initiator caspases  and the other involves cytochrome-c release . There is evidence for the occurrence of one of the apoptotic pathways induced by cytochrome-c in the placenta of tumour-bearing rats and in rats injected with ascitic fluid. Further studies need to address other apoptotic pathways involved during tumour growth in placenta. Hung et al.  reported that hypoxia-reoxygenation in vitro stimulated apoptosis in human placental tissue, and that there was a significant increase in cytochrome-c release from mitochondria associated with intense immunolabelling for active caspase 3 in the syncytiotrophoblast and foetal endothelial cells. There was also increased labelling of syncytiotrophoblastic nuclei for cleaved PARP, and higher cytosolic concentrations of cleaved PARP in placental tissue under hypoxia .
In agreement with these findings, we observed increased caspase 3 expression in groups W and A that may have been initiated by the release of cytochrome-c into the cytosol . Indeed, the injection of ascitic fluid increases caspase 3 activity , which then cleaves PARP, one of many caspase substrates, thereby preventing this enzyme from repairing damaged DNA ; this lack of repair can lead to apoptosis. Western blotting showed an increase in cleaved PARP and caspase 3 expression in groups W and A that was also associated with a progressive enhancement of the cytochrome-c levels in both groups. These results may indicate that placental layers, especially the trophoblast, may experience greater apoptosis mediated by cytochrome-c release and caspases, including caspase-3, which is activated by several death receptors . Such activation could be related to the decrease in GST activity seen in groups W and A. This would allow the formation of reactive oxygen species , which could in turn activate other apoptotic pathways [50, 51]. Various studies have reported increased apoptosis following B19 infection of villous trophoblastic cells , an elevation in caspase 3 activity and cytochrome-c release in chorionic villi after exposure to ultrasound , and higher apoptotic rates in placentas from pregnancies complicated with intrauterine growth restriction .