Dopaminergic receptors in human prolactin-secreting adenomas: a quantitative study.
Dopaminergic receptors were observed on the membranes of 26 human PRL-secreting adenomas. Two binding sites were found for [3H]domperidone, a selective dopamine antagonist, with a Kd1 of 0.29 +/- 0.06 nM and a Kd2 of 4.19 +/- 0.7 nM (n = 5). Bmax1 and Bmax2 (maximum numbers of binding sites, first and second sites, respectively) varied from one adenoma to another. When considering Bmax1, two different categories of PRL-secreting adenomas were distinguished, one with a concentration of receptor over 250 fmol/mg protein and others with lower concentrations of receptor (< 250 fmol/mg protein). In the latter, when considering the volume of the tumor, a higher plasma PRL level was found. Two binding sites for [3H]domperidone also were found in the normal human hypophysis with Kd values similar to those of the adenomas (0.18 +/- 0.04 and 3.95 +/- 0.35 nM). The same number of binding sites was observed in normal pituitaries and in PRL-secreting adenomas. However, when considering the density of PRL-secreting cells in the two different tissues (prolactinomas contain 2 or 3 times more PRL-secreting cells than human pituitary tissue), one may suspect a defect in the dopaminergic inhibiting control in PRL-secreting adenomas.
D000236:Adenoma / Q000378:metabolism*; D000293:Adolescent; D000328:Adult; D000368:Aged; D001562:Benzimidazoles / Q000378:metabolism; D001667:Binding, Competitive; D002462:Cell Membrane / Q000378:metabolism; D004294:Domperidone; D005260:Female; D006801:Humans; D007700:Kinetics; D008297:Male; D008875:Middle Aged; D010880:Piperidines / Q000378:metabolism; D010902:Pituitary Gland / Q000378:metabolism; D010911:Pituitary Neoplasms / Q000378:metabolism*; D011388:Prolactin / Q000378:metabolism*; D011954:Receptors, Dopamine / Q000378:metabolism*
D001562:Benzimidazoles; D010880:Piperidines; D011954:Receptors, Dopamine; D004294:Domperidone; D011388:Prolactin