The present study was conducted to establish whether growth hormone (GH) releasing factor (GRF) is present in porcine placenta. Various concentrations of placental extracts from sows at 90 and 110 days of gestation were added to porcine anterior pituitary cells in culture. The extract-induced GH secretion was compared to that of GRF(1-29)NH2. Experiments were also performed in the presence of the GRF receptor antagonist N alpha-acetyl(D-Arg2-Ala15) rat GRF(1-29)NH2 (10(-7) M). Significant effects on GH production were obtained with increasing concentrations of placental extracts (p < 0.001). This response was significantly diminished in the presence of the GRF receptor antagonist (p < 0.001). The effect of gestational age at the time of collection of the placenta was nonsignificant (p > 0.1). In addition, using a placental extract from 110 days of gestation, an immunoreactive GRF content of 52-63 ng/mg dry weight was detected. Altogether, the detection of an immunoreactive GRF-like substance in porcine placental extracts and the ability of these extracts to stimulate GH release in a concentration-dependent manner, likely by triggering a GRF-receptor-mediated mechanism, support the presence of GRF in this tissue.