Application of new homologous in vitro bioassays for human lactogens to assess the actual bioactivity of human prolactin isoforms in hyperprolactinaemic patients.
BACKGROUND
Prolactin (PRL) plays a central role in mammary gland development and lactation. Due to its molecular heterogeneity, measurement of PRL immunoreactivity does not necessarily reflect its intrinsic bioactivity. For many years the Nb2 rat lymphoma cell bioassay has been the only reference bioassay for human lactogens. This bioassay, however, does not always correlate with the clinical features found in some patients exhibiting normal or elevated immunoreactive serum PRL concentrations.


OBJECTIVE
(1) To determine the concentrations of bioactive PRL in serum samples from individuals with normoprolactinaemia or with different forms of hyperprolactinaemia using two recently described homologous in vitro bioassays (i.e. a transcriptional bioassay in HEK-293 cells and a proliferation assay in Ba/F3 cells); and (2) to compare these results with those generated by the classical Nb2 cell bioassay.


METHODS
Cross-sectional study.


METHODS
An institutional biomedical research laboratory.


METHODS
Ten patients with symptomatic hyperprolactinaemia due to prolactinoma, 11 patients with asymptomatic hyperprolactinaemia and macroprolactinaemia, and nine normal women.


METHODS
Measurement of immunoreactive and bioactive concentrations of serum PRL.


RESULTS
Samples from normal women and patients with tumoral hyperprolactinaemia due to prolactinoma exhibited similar within-group concentration values of bioactive and immunoreactive serum PRL when tested by the three bioassays and the immunoradiometric assay employed. By contrast, measurement of bioactive PRL in samples from patients with macroprolactinaemia revealed that macroprolactin was poorly active in the homologous receptor bioassays, while it was more active in the Nb2 bioassay.


CONCLUSIONS
The reduced bioactivity of PRL in patients with macroprolactinaemia may further explain the absence of clinical features of hyperprolactinaemia in these individuals. In addition, our findings indicate that species-specificity and sensitivity of the bioassays are determinant factors in the measurement of the intrinsic biological activity of circulating PRL.
Leaños-Miranda
Alfredo
A
Research Unit in Reproductive Medicine, Hospital de Ginecología y Obstetricia Luis Castelazo Ayala, Instituto Mexicano del Seguro Social, México D.F., Mexico. alfredolm@yahoo.com
Cárdenas-Mondragón
Guadalupe
G
Rivera-Leaños
Roxana
R
Ulloa-Aguirre
Alfredo
A
Goffin
Vincent
V
D000328:Adult; D000818:Animals; D001402:B-Lymphocytes / Q000378:metabolism; D001681:Biological Assay; D002460:Cell Line; D049109:Cell Proliferation; D002845:Chromatography; D002850:Chromatography, Gel; D002999:Clone Cells; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D006966:Hyperprolactinemia / Q000097:blood*; D015592:Immunoradiometric Assay; D007457:Iodine Radioisotopes; D007668:Kidney / Q000196:embryology; D008297:Male; D051379:Mice; D011388:Prolactin / Q000097:blood*; D011485:Protein Binding; D011869:Radioligand Assay; D014162:Transfection
D007457:Iodine Radioisotopes; D011388:Prolactin