Interaction of growth hormone-releasing hormone with the insulin-like growth factors during prenatal development in the rat

The placenta is a chimeric organ that produces all the components of the hypothalamic-pituitary GH axis. We propose that placental GH-releasing hormone (GHRH) stimulates placental GH-like hormones which in turn stimulate production of the insulin-like growth factors (IGFs), IGF-I and IGF-II, and these placental IGFs are important for growth and development of the placenta as well as the fetus. To test this hypothesis, pregnant rats were given either GHRH antisera or preimmune sera ip from days 7–19 of gestation. Fetuses were killed on day 19, and IGF-I and IGF-II tissue and serum concentrations in the mother and fetus were measured by RIA. IGF-II receptor content was measured by Western analysis. IGF-I and IGF-II messenger (m) RNA levels were measured in the placentas as well as in the fetal livers. The GHRH antibody titer was highest at day 19 of gestation but continued to be present through day 20 of postnatal development. Although placental weights did not differ, antibody-treated animals had higher pl...