Expression of Prolactin-Releasing Peptide and Its Receptor Messenger Ribonucleic Acid in Normal Human Pituitary and Pituitary Adenomas1

The recently identified PRL-releasing peptide (PrRP) is the first hypothalamic peptide hormone that specifically stimulates PRL production from the pituitary gland. Similar to other hypothalamic regulatory hormones, it acts through 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 tumors. PrRP mRNA was expressed in all five normal pituitary glands examined. In contrast, PrRP mRNA was detected in only 5 of 11 of the human prolactinomas. All 5 prolactinomas expressing PrRP were responsive to dopamine agonist treatment, whereas PrRP-negative prolactinomas were non- or partially responsive. PrRP mRNA was also detected in 6 of 13 GH-secreting tumors and 5 of 10 clinically nonfunctioning tumors investigated. PrRP receptor mRNA was found in all the normal and neoplastic human pituitary samples studied. The production of PrRP and its receptor by normal and neoplastic pituitary tissue raises the question of whether it may regulate PRL production in an autocrine/paracrine manner in pituitary tissue. Further investigation of PrRP and its receptor expression and function will be needed to clarify its potential role in regulating PRL secretion in normal human lactotrophs and pituitary tumors.