Ovulação e desenvolvimento uterino, placentário e fetal em marrãs gestantes tratadas com tiroxina

Abstract

The aim of this study was to evaluate the effect of administration of thyroxine on ovulation and fetal and placental, uterine development in gilts at 70 days of gestation. 20 gilts, middle-sisters, and daughters of F1 females with a male, ¾ Landrace X ¼ Large White were used. At 150 days of age, i.e., before first heat, the animals were randomly divided into two groups: treated (n = 10) and control (n = 10). The treated group received a daily dose of 400g of L-thyroxine (T4) in the diet until three days before slaughter and the control group received only diet. Beforeartificial insemination, blood was collected for determination of plasma total T4. The gilts were inseminated in the second oestrus and slaughtered at 70 days of gestation. The thyroid follicular epithelium height of fetuses, number, size and weight of fetuses, corpora lutea number, embryonic mortality rate, uterus and placenta weights and placental liquids volume were determinated. Five fragments of the uterine-placental interface from each gilt were randomly collected for histomorphometric and immunohistochemistry analysis. Height of the endometrial epithelium, endometrial glands and of the trophoblast, uterine layers thickness and immunohistochemical expression of vascular endothelial growth factor (VEGF) in the uterus and placenta were determined. The number of vessels/field was also measured in histological sections of uterus and placenta immunostaining for factor VIII that is expressed in endothelial cells. The averages of all variables were compared by Student t test. Before insemination the gilts showed clinical signs of hyperthyroidism characterized by significant increase in plasmalevels of T4, mild exophthalmos and behavioral change characterized by aggression and agitation. At 70 days of gestation, administration of thyroxine showed positive effect in the uterus and placenta. The height of the trophoblastic epithelium, endometrial epithelium and endometrial glands epithelium was significantly higher in the group treated with T4. The expression of cytoplasmatic and nuclear VEGF in trophoblastic cells was also significantly higher in the placenta of gilts treated with T4. But the uterine and placental vessels number did not differ between groups (pº0.06). The other parameters did not show significant differencesbetween groups (p>0.05). We conclude that oral administration of 400g of the T4 up to 70 days of pregnancy in gilts increases the height of the endometrial epithelium, trophoblastic epithelium and of the endometrial glands epithelium and increases the trophoblastic expression of VEGF, but did not increase the ovulation rate, number of fetuses, fetal development and placentary vascularization.