Antibodies-Online Prolactin-releasing peptide is a specific prolactin releasing peptide. Antibodies-Online prolactin-releasing peptide (PrRP) was originally isolated as an endogenous hypothalamic ligand for the hGR3 orphan receptor and has been shown to release prolactin from dispersed pituitaries harvested from lactating female rats and only at very high doses in cycling females. PrRPs have no effect on prolactin production from dispersed pituitary cells harvested from males.