Effect of triiodothyronine on developmental competence of bovine oocytes.

Developmental competence of in vitro-matured bovine oocytes is a limiting factor in production of embryos in vitro. Several studies have suggested a potential positive effect of thyroid hormones on cultured oocytes and/or their supporting cells. Therefore, the aim of the present study was to ascertain whether medium supplementation with triiodothyronine (T3) improved subsequent developmental competence of in vitro-matured bovine oocytes. For this purpose, we first documented (using reverse transcription PCR) that whereas bovine cumulus cells expressed both thyroid hormone receptor (TR)-α and TRß, immature bovine oocytes expressed TRα only. Thereafter, to test the effects of TH on developmental competence, abattoir-derived oocytes were matured in vitro in a medium containing 0, 25, 50, or 100 nM T3 and subjected to in vitro fertilization. Embryo quality was evaluated by assessing cleavage and blastocyst rates, morphological quality, development kinetics, and total cell number on Day 8 of culture. Notably, addition of 50 or 100 nM T3 to the in vitro maturation medium increased (P < 0.05) the rate of hatched blastocysts on the eighth day of culture, as compared with other groups (62.4 ± 11.7, 53.1 ± 16.3, and 32.4 ± 5.3, respectively). Next, the relative expression levels of genes related to embryo quality POU-domain transcription factor (POU5F1) and glucose transporter-1 (GLUT 1) were compared between in vivo- and in vitro-produced blastocysts. On the basis of the previous experiments, IVP embryos originating from oocytes that were matured in vitro in the presence or absence of 50 nM T3 were evaluated. The treatment had no effect (P > 0.05) on gene expression. We concluded that supplementation of bovine oocyte in vitro maturation medium with T3 may have a beneficial effect on the kinetics of embryo development.

Evaluation of apoptosis as a mechanism of follicular cell atresia in the ovaries of cattle (bos indicus) and buffalo (bubalus bubalis) fetuses

The objective of this study was to investigate the occurrence of apoptosis in the ovaries of cattle and buffalo fetuses between 4 and 8 months old by the terminal deoxynucleotidyltransferase - mediated dUTP nick end labeling (TUNEL) assay . Histological analysis of the ovarian t issue showed that apoptosis occurred at all ages evaluated , presenting a similar pattern among different fetal stages in both species . Within species, secondary follicles displayed a higher (P 0.05) of apoptotic follicular cells among the three follicular classes compared . C omparing resul ts between species, secondary follicles had a higher (P < 0.05) mean number of TUN EL positive cells in bovine fetuses; however , this difference was proportional to the larger number of follicular cells present in secondary follicles in this species . In summary, the TUNEL method was effective for the detection of apoptosis in the support ing cells of ovarian follicles from bovine and buffalo fetuses with apoptosis occurring at similar rates in both species between 4 and 8 months of gestational age. Further studies are needed to better understand the dynamics of apoptosis as a regulator of follicular atresia in fetal ovaries from these species, as well as the potential involvement of the oocyte in this process.