Expression of prolactin-releasing peptide and its receptor messenger ribonucleic acid in normal human pituitary and pituitary adenomas

The recently identified PRL-releasing peptide (PrRP) is the first hypothala mic peptide hormone that specifically stimulates PRL production from the pi tuitary gland. Similar to other hypothalamic regulatory hormones, it acts t hrough its specific seven-transmembrane domain, G protein-coupled receptor. Using RT-PCR, we examined messenger ribonucleic acid (mRNA) expression of PrRP and its receptor in normal human pituitary tissue and in pituitary tum ors. PrRP mRNA was expressed in all five normal pituitary glands examined I n contrast, PrRP mRNA was detected in only 5 of 11 of the human prolactinom as. All 5 prolactinomas expressing PrRP were responsive to dopamine agonist treatment, whereas PrRP-negative prolactinomas were non- or partially resp onsive. PrRP mRNA was also detected in 6 of 18 GH-secreting tumors and 5 of 10 clinically nonfunctioning tumors investigated. PrRP receptor mRNA was f ound in all the normal and neoplastic human pituitary samples studied. The production of PrRP and its receptor by normal and neoplastic pituitary tiss ue raises the question of whether it may regulate PRL production in an auto crine/paracrine manner in pituitary tissue. Further investigation of PrRP a nd its receptor expression and function will be needed to clarify its poten tial role in regulating PRL secretion in normal human lactotrophs and pitui tary tumors.