Objective: The objective of the study was to characterize the bioactivity of prolactin (PRL) in hyperprolactinaemic patients with prolactinomas, irregular menstrual cycles, regular menstrual cycles and PCOS.
Methods: Serum PRL, biological activity of PRL (after polyethylene glycol (PEG) precipitation) and serum follicle stimulating hormone (FSH), luteinizing hormone (LH), estradiol (E2), testosterone (T), thyroid-stimulating hormone (TSH) concentrations were measured in all hyperprolactinaemic patients and control group (healthy subjects). Correlations between active PRL (PRL-PEG) and serum FSH, LH, E2, T, TSH concentrations were also evaluated.
Results: Prolactinoma is characterized by high serum PRL levels and its high biological activity. Hyperprolactinaemic patients with irregular cycles were characterized by high biological activity of PRL. Patients with hyperprolactinaemia and regular cycles had low biological activity of PRL.
Conclusions: Diagnosis of hyperprolactinaemia should be associated with estimation of PRL biological activity because it is important for type of hyperprolactinaemia management. Low biological activity of PRL does not impair FSH and LH secretion and does not cause hypoestrogenism.