Temporal profile of GDF-8 in hamster uterus during pregnancy: (A) mRNA expression and (B) cleaved form of the protein. Total RNA from uterus collected at designated time points post coitus was extracted, reversely-transcribed and subjected to real time PCR for amplification of GDF-8. Data were expressed as mean ± S.E.M. To determine how pregnancy affected GDF-8 expression, data from pregnant uterus was compared with non-pregnant uterus at day of estrous (D0) by Student's t-test (*P < 0.05; ***P < 0.01) (Number of animals: D0:6; D2.5:4, D3:4, D5:3, D7:5, D9:5, D15:4). There was a significant reduction in GDF-8 mRNA from D3 onwards. At D2.5 (open squares) the uterus was free of embryos. From D3 onwards (closed squares), embryos were in the uterus. To find out if the presence of embryos affected GDF-8 mRNA expression, data from D3 to D15 were compared with that of D2.5 by one-way ANOVA and a significant decrease was noted only in the D9 uterus #P < 0.05). (B) Total uterine proteins at various post coital time points were extracted to determine the amount of active GDF-8 peptide by ELISA. Likewise, data were expressed as mean ± S.E.M. Data from pregnant uteri (closed squares) were compared with that of non-pregnant uterus at estrus (D0, open squares) by Student's t-test (***P < 0.01) (Number of animals at each time point =3). The amount of active GDF-8 in pregnant uterus was significantly higher than that of non-pregnant uterus. One-way ANOVA was used to determine the effect of the presence of embryos in uterus on active GDF-8 level. The presence of embryo at D3, D5 and D9 has significantly higher level of active GDF-8 (#P < 0.05; ###P < 0.01 compared with D2.5).