Regional distribution of immunoreactive prolactin-releasing peptide in the human brain

Regional distribution of prolactin-releasing peptide (PrRP) in the human brain was studied by radioimmunoassay. The antiserum raised against human PrRP-31 in a rabbit was used in the assay, which showed 100% cross reaction with PrRP-20 and no significant cross reaction with other peptides. The highest concentrations of immunoreactive-PrRP were found in hypothalamus (912 +/- 519 fmol/g wet weight, n = 6, mean +/- SEM), followed by medulla oblongata (496 +/- 136 fmol/g wet weight) and thalamus (307 +/- 117 fmol/g wet weight). On the other hand, immunoreactive-PrRP was not detected in frontal lobe or temporal lobe (<50 fmol/g wet weight). Sephadex G50 column chromatography of the immunoreactive-PrRP in the hypothalamus and medulla oblongata showed three immunoreactive peaks; one peak eluting in the position of PrRP-20, one eluting in the position of PrRP-31 and one eluting earlier. Reverse phase high-performance liquid chromatography (HPLC) of these brain tissue extracts showed a peak eluting in the position of PrRP-20 and PrRP-31. The present study has shown for the first time the presence of immunoreactive-PrRP in the human brain. The immunoreactive-PrRP levels in the human hypothalamus were, however, lower than the levels of other neuropeptides with prolactin-releasing activity, such as thyrotropin-releasing hormone and vasoactive intestinal polypeptide.