PROLACTIN RECEPTORS IN HUMAN PITUITARY-ADENOMAS

OBJECTIVE In the rat, prolactin receptors (PRL-R) have been identified in normal pituitary cells and in anterior pituitary tumours induced b y oestradrol. No published data are available concerning PRL-R in the human pituitary. The aim of our study was therefore to detect the pres ence of PRL-R in the normal human pituitary gland and human pituitary adenomas. DESIGN Evaluation of free and total PRL-R in the normal pitu itary gland and different pituitary tumours characterized by immunocyt ochemical analysis. PATIENTS Twenty-six unselected patients (14M, 12F) who underwent surgery for pituitary adenoma (3 prolactinomas, 4 GH-PR L adenomas, 5 GH adenomas, 1 ACTH adenoma, 9 glycoprotein and/or alpha -subunit adenomas, 4 null cells adenomas) were studied. Nine pituitari es from subjects whose death was unrelated to brain and endocrine dise ases, were also studied as a control group in the PRL binding studies. MEASUREMENTS Free PRL-R in microsomal membranes were determined by in -vitro radioreceptor assay using I-125-labelled human PRL as ligand. T otal PRL-R were also measured in the same membrane fractions by removi ng endogenous PRL bound to its receptors using 4 MgCl2. Serum PRL leve ls were also evaluated in all patients before surgery using an IRMA me thod. RESULTS Specific binding values for PRL (free PRL-R) were 0.39 /- 0.03% (range 0-1.96%) in the pituitary adenomas. These binding valu es were identical to those observed in normal pituitaries (0.38 +/- 0. 07%, range 0.1-0.78%). Elevated PRL binding (1.25% and 1.96%) was foun d in two patients with PRL secreting adenomas and very high serum PRL levels (5768 and 11240 mU/L. No PRL binding was shown in 4 patients. T reatment of membranes with 4M MgCl2 increased the specific binding (to tal PRL-R) in both pituitary tumours (0.5 +/- 0.11%; P < 0.001) and no rmal pituitaries (0.47 +/- 0.07%; P < 0.02). CONCLUSIONS Our data have demonstrated the presence of prolactin receptors in normal cadaveric pituitary and in most pituitary adenomas, irrespective of histological classification. In particular, elevated prolactin receptor levels wer e shown in PRL-secreting tumours from patients with markedly increased serum PRL levels. Our study may support several lines of experimental evidence for a specific functional role for PRL in the growth of some pituitary adenomas.