Locations and molecular forms of gastrin-releasing peptide-like immunoreactive entities in ovine pregnancy

Large quantities of gastrin-releasing peptide-like immunoreactivity (GRP-LI) are present in ovine pregnancy fluids (allantoic fluid > fetal plasma > esophageal fluid = amniotic fluid = urine > maternal plasma) and in term endometrium (60 +/- 29 pmol.g-1) and myometrium (4.5 +/- 1.2 pmol.g-1). The larger molecular size [greater than GRP (1-27)] of this GRP-LI entity is not due to a GRP binding protein nor to a C-terminal extension of GRP. In contrast, ovine fetal colon extracts appear to contain the usual GRP (1-27) and GRP (18-27) forms. Hence, the uterus, not the fetus, is the probable source of this novel GRP-like peptide. It apparently acts as a hormone in ovine pregnancy and may play an important role in fetal-placental development.