PRESENCE OF A BIOACTIVE AND IMMUNOREACTIVE GROWTH-HORMONE-RELEASING-FACTOR-LIKE SUBSTANCE IN PORCINE PLACENTA

The present study was conducted to establish whether growth hormone (G H) releasing factor (GRF) is present in porcine placenta. Various conc entrations of placental extracts from sows at 90 and 110 days of gesta tion were added to porcine anterior pituitary cells in culture, The ex tract-induced GH secretion was compared to that of GRF(1-29)NH2. Exper iments were also performed in the presence of the GRF receptor antagon ist N-alpha-acetyl(D-Arg(2)-Ala(15)) rat GRF(1-29)NH2 (10(-7) M). Sign ificant effects on GH production were obtained with increasing concent rations of placental extracts (p < 0.001). This response was significa ntly diminished in the presence of the GRF receptor antagonist (p < 0. 001). The effect of gestational age at the time of collection of the p lacenta was nonsignificant (p > 0.1). In addition, using a placental e xtract from 110 days of gestation, an immunoreactive GRF content of 52 -63 ng/mg dry weight was detected. Altogether, the detection of an imm unoreactive GRF-like substance in porcine placental extracts and the a bility of these extracts to stimulate GH release in a concentration-de pendent manner, likely by triggering a GRF-receptor-mediated mechanism , support the presence of GRF in this tissue.