SHORT COMMUNICATION maternal thyroid dysfunction and c- fos and c- jun expression in rat placenta

The effects of hypothyroidism and hyperthyroidism on placental Hofbauer cells of pregnant rats

We investigated the effects of maternal thyroid disorders on Hofbauer cells of both the placenta and the fetus in pregnant rats. We divided 21 rats into three groups: control group, induced hypothyroidism (hypo) group and induced hyperthyroidism (hyper) group. Hypothyroidism was induced using propylthiouracil and hyperthyroidism was induced using L-thyroxine. We measured maternal weight, maternal free thyroxine, fetal weight, fetal viability and placental morphology. At the end of the experiment, fetuses of the hypo and hyper groups were less developed than those of the control group. In the hypo and hyper groups, the thickness of the labyrinth zone was decreased, but thickness of the basal zone and decidua basalis was increased. The number of Hofbauer cells was increased in both the hypo and hyper groups. Vascular endothelial growth factor expression was increased in both the hypo and hyper groups compared to controls. Our findings indicate that maternal thyroid disorders exert a negative effect on fetal growth and placental development.

Thyroid hormones and female reproduction

Thyroid hormones are vital for the proper functioning of the female reproductive system, since they modulate the metabolism and development of ovarian, uterine, and placental tissues. Therefore, hypo- and hyperthyroidism may result in subfertility or infertility in both women and animals. Other well-documented sequelae of maternal thyroid dysfunctions include menstrual/estral irregularity, anovulation, abortion, preterm delivery, preeclampsia, intrauterine growth restriction, postpartum thyroiditis, and mental retardation in children. Several studies have been carried out involving prospective and retrospective studies of women with thyroid dysfunction, as well as in vivo and in vitro assays of hypo- and hyperthyroidism using experimental animal models and/or ovarian, uterine, and placental cell culture. These studies have sought to elucidate the mechanisms by which thyroid hormones influence reproduction to better understand the physiology of the reproductive system and to provide better therapeutic tools for reproductive dysfunctions that originate from thyroid dysfunctions. Therefore, this review aims to summarize and update the available information related to the role of thyroid hormones in the morphophysiology of the ovary, uterus, and placenta in women and animals and the effects of hypo- and hyperthyroidism on the female reproductive system.

Fetal growth restriction in hypothyroidism is associated with changes in proliferative activity, apoptosis and vascularisation of the placenta

The objective of this study was to evaluate fetal weight, histomorphometric changes and proliferative activity, apoptosis and angiogenesis of the placenta in rats with hypothyroidism. Thirty-six adult female rats were divided into two groups with 18 animals each: control and hypothyroidism. Hypothyroidism was induced by daily administration of propylthiouracil (1 mg/animal). The administration began five days before becoming pregnant and the animals were sacrificed at 14 or 19 days of gestation. The control group received a placebo. The number and weight of fetuses and the rate of fetal death was determined, as well as the morphometric characteristics, the immunohistochemical expression of cell division control protein 47 (CDC)-47 and vascular endothelial growth factor (VEGF) and the number of apoptotic cells in the placental disk. The data were analysed by Mann–Whitney U test. Hypothyroidism reduced the weight of fetuses and of the uterus and placenta (P < 0.05), altered the thickness of the placental labyrinth and spongiotrophoblast (P < 0.05), increased the population of glycogen cells in the spongiotrophoblast (P < 0.05), interfered with the vascular development of the placental labyrinth and decreased VEGF expression (P < 0.05), reduced the expression of CDC-47 and cellularity and increased the apoptotic rate in the placental disk (P < 0.05). We conclude that hypothyroidism affects fetal weight by altering the proliferative activity, apoptosis and vascularisation of the placenta.

Thyroid hormone receptor expression in rat placenta

The expression of c- erbAalpha and -beta encoded thyroid hormone receptors (TR) was investigated in rat placenta between 16 and 21 days of gestation (dg), and in fetal liver and brain at 16 dg, using semi-quantitative RT-PCR and nuclear 3,5,3'-triiodothyronine (T(3)) binding. TRalpha1, TRbeta1, c- erbAalpha 2 and c- erbAalpha 3 mRNA abundance was unchanged in placenta between 16 and 21 dg, as was the dissociation constant (K(d)) of T(3) binding. The maximal T(3) binding capacity (B(max)) in placenta doubled over this period, suggesting placental TR binding activity is post-transcriptionally regulated. Transcript abundance in tissues at 16 dg can be summarized: TRalpha1, placenta=fetal liver<fetal brain; TRbeta1, placenta=fetal liver>fetal brain; c- erbAalpha 2 and alpha3, placenta=fetal liver<fetal brain; TRbeta2; none detected. T(3)binding in fetal liver and brain exhibited equivalent K(d) and B(max), the K(d) being less than 50 per cent of that in placenta, though B(max) was unchanged. The higher K(d)in placenta may reflect tissue-specific patterns of TR modification. In conclusion, rat placenta expresses significant levels of c- erbAalpha and -beta transcripts and protein, providing a possible mechanism of action for T(3) of maternal and fetal origin in this tissue.