Exogenous somatotropin alters IGF axis in porcine endometrium and placenta

The aim of this study was to examine whether exogenous somatotropin (ST) can alter the insulin-like growth factor (IGF) axis in the porcine epitheliochorial placenta. Crossbred gilts were injected either 6 mg of recombinant porcine ST or vehicle from days 10 to 27 after artificial insemination (term day 116). Control and ST-treated gilts were euthanized on day 28 (8 control/5 treated), day 37 (4 control/6 treated), and day 62 (4 control/6 treated) of gestation. Endometrium and placental tissue samples were collected and subjected to mRNA analyses. In control gilts, somatotropin receptor (STR) and IGF-I mRNA abundance in the endometrium decreased with gestation. Conversely, the amounts of IGF-II mRNA and of IGF binding protein (BP)-2 and -3 mRNA, which were analyzed in endometrium and placental chorion, increased with gestation. The endometrium contained less IGF-II mRNA but more IGFBP-2 and-3 mRNA than the placental chorion. In response to pST treatment, the amounts of endometrial STR and IGF-I mRNA were lower at days 28 and 37, but higher at day 62 of gestation. The content of IGF-II mRNA was higher in the endometrium of pST-treated than control gilts on day 37. The amount of IGFBP-2 mRNA was increased on day 37 in endometrium and placenta of pST-treated gilts, whereas no changes in IGFBP-3 mRNA were observed. The IGF-II/IGFBP-2 ratio was higher in the placenta in response to pST on day 28 of gestation. Results show that pST treatment of pregnant gilts during early gestation alters IGF axis in maternal and fetal placental tissues and suggest pST may exert an effect on fetal growth by altering the relative amount of IGFBPs and IGFs at the fetal-maternal interface.