Large Molecular Weight Immunoreactive Corticotrophin‐Releasing Hormone has Bioactivity on Superfused Ovine Pituitary Cells

Human placental extracts fractionated with Sephadex G‐50 produced three peaks of corticotrophin‐releasing hormone immunoreactivity, a large molecular weight peak (Mr30,000), an intermediate peak (4,758 < Mr < 10,000) and a low molecular weight peak coeluting with the 41‐residue hormone. All three peaks of immunoreactivity stimulated the release of β‐endorphin‐like immunoreactivity from ovine pituitary cells superfused in vitro. No response was observed from unstimulated cells superfused in parallel. Gel chromatography indicated that intermediate and small molecular weight forms of human corticotrophin‐releasing hormone immunoreactivity remained intact after contact with the ovine pituitary cells, whereas the large molecular weight material dissociated to produce 41‐residue hormone immunoreactivity. The secreted β‐endorphin immunoreactivity was shown by gel chromatography to comprise both β‐lipotrophin‐like and the 31‐residue β‐endorphin‐like immunoreactivity. The data show that the intermediate and low molecular weight forms of placental corticotrophin‐releasing hormone immunoreactivity are bioactive and suggest that the intermediate form is a hormone precursor, possibly procorticotrophin‐releasing hormone125–196, and the small form is identical to the hypothalamic hormone. The results with the larger molecular weight material indicate that it is likely to be a complex of the mature 41‐residue hormone and a binding protein.