Ontogeny and Nutritional Programming of the Hepatic Growth Hormone-Insulin-Like Growth Factor-Prolactin Axis in the Sheep

Abstract

The liver is an important metabolic and endocrine organ in the fetus, but the extent to which its hormone receptor sensitivity is developmentally regulated in early life is not fully established. Therefore, we examined developmental changes in mRNA abundance for the GH receptor (GHR) and prolactin receptor (PRLR) plus IGF-I and -II and their receptors. Fetal and postnatal sheep were sampled at either 80 or 140 d gestation, 1 or 30 d, or 6 months of age. The effect of maternal nutrient restriction between early gestation to midgestation (i.e. 28–80 d gestation, the time of early liver growth) on gene expression was also examined in the fetus and juvenile offspring. Gene expression for the GHR, PRLR, and IGF-I receptor increased through gestation peaking at birth, whereas IGF-I was maximal near to term. In contrast, IGF-II mRNA decreased between midgestation and late gestation to increase after birth, whereas IGF-II receptor remained unchanged. A substantial decline in mRNA abundance for GHR, PRLR, and IGF-I receptor then occurred up to 6 months. Maternal nutrient restriction reduced GHR and IGF-II receptor mRNA abundance in the fetus, but caused a precocious increase in the PRLR. Gene expression for IGF-I and -II were increased in juvenile offspring born to nutrient-restricted mothers. In conclusion, there are marked differences in the ontogeny and nutritional programming of specific hormones and their receptors involved in hepatic growth and development in the fetus. These could contribute to changes in liver function during adult life.