Functions gestation

Fetal TH must come from the maternal circulation before the fetal thyroid gland and pituitary—thyroid axis become functional (gestation day (GD) 17—18 in rats and 90 in humans). Maternal transfer of thyroxine (T4) constitutes a major fraction of fetal TH even after the onset of fetal thyroid secretion, they may contribute to the maintenance of fetal development (Burrow et ai, 1994). Therefore, changes in maternal TH levels have an affirmative effect on fetal TH metabolism. Depending on the dose of iodine, the susceptibility of individuals, and previous conditions of the gland, iodine excess can induce maternal hypothyroidism or hyperthyroidism. In a case reported by Serreaul et al. (2004), an obvious thyroid goiter was found in the fetus after excessive maternal iodine... 

Recently, there has been increasing interest in the development of test methods to assess the possible adverse functional effects of exposing the fetus, both early and late in gestation (112,113). 

The vasculature is established by the 18th day of gestation in rats, and comes from the arterial supply as the anterior cerebral vessel, eventually entering the basal lamina via septal tributaries of the olfactory artery (Szabo, 1988). Unlike the MOE, the organ s capillaries penetrate in loops into the neuroepithelium. Blood from the vomeronasal complex arrives for collection in the vomeronasal vein, as described earlier [Fig. 2.11(a)]. The establishment of the highly vascular columnar complexes seen in the ophidian organ has not been correlated with functional development (c.f. Wang and Halpem, 1980 Holtzman and Halpem, 1990). 

As hydrogen sulfide is a neurotoxic agent, an inhalation study examining potential developmental neurotoxicity is needed. Such studies should include a battery of tests to examine the function of the nervous system in the offspring of animals exposed to hydrogen sulfide during gestation or for various periods before adulthood. 

The rat cell line R3/1 was established from cells obtained from broncho-alveolar tissues of foetal Wistar rats at 20 days of gestation. This cell line displays a phenotype with several characteristic features of ATI cells. R3/1 cells were analysed to show a positive expression for mRNA and protein content of markers related to the ATI cell type (e.g., Tla, ICAM-1, connexin-43 and caveolin-1 and -2) [79], Whether or not this cell line can form functional tight junctions is currently under investigation in our laboratories. 

It needs to be mentioned here that there remains some controversy over the placental expression of P-gp as a function of gestational age. An immunohis-tochemical study done by Macfarland et al. showed that P-gp was localized to the microvillous border of trophoblasts in first trimester placenta, but not in term placenta [85], Subsequent studies refuted this to show that MDR1 mRNA is present throughout pregnancy [94], More recently, enzyme-linked immunosorbent assay (ELISA) performed in syncytial microvillous membrane showed that P-gp protein expression in early gestational age placenta is about... 

H.E. Meyer Zu Schwabedissen, M. Grube, B. Heydrich, K. Linnemann, C. Fusch, H.K. Kroemer, and G. Jedlitschky. Expression, localization, and function of MRP5 (ABCC5), a transporter for cyclic nucleotides, in human placenta and cultured human trophoblasts Effects of gestational age and cellular differentiation. Am J Pathol. 166 39 18 (2005). 

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