Secretory dynamics of bioactive and immunoreactive prolactin in polycystic ovary syndrome

[True and false hyperprolactinemia: how to discriminate one from the other in infertility management?]

Serum prolactin measurement is usually performed in infertility evaluation, even if there's no specific clinical presentation of hyperprolactinemia. High levels of prolactin are noted in 20 to 30% of menstrual abnormalities and in about 10% of regular menses. It is of importance to determine whether hyperprolactinemia is related to pituitary adenoma, drug administration, general diseases, or circulating large forms of prolactin, in order to avoid heavy, expensive, time consuming and unnecessary clinical investigations or therapeutic actions. We must first to confirm the biological diagnosis of hyperprolactinemia with few repeated plasmatic measurements, and, later, if necessary use TRH-metoclopramide test and/or pituitary magnetic resonance imaging.

Hypothalamic dopaminergic tone and prolactin bioactivity in women with polycystic ovary syndrome

BACKGROUND

The present study was carried out to investigate the functional significance of the reduced dopaminergic tone in subjects affected with polycystic ovary syndrome (PCOS).

METHODS

Our group evaluated the response of pituitary PRL, LH, FSH, and TSH to the administration of a single 10-mg oral dose of the dopamine (DA) receptor antagonist metoclopramide in lean (n = 7) and obese (n = 8) PCOS women and in 11 regularly cycling age- and weight-matched controls (six lean and five obese). In addition, circulating PRL bioactivity was evaluated by its mitogenic activity on a lymphoma cell bioassay.

RESULTS

Oral administration of metoclopramide resulted in a significant increase in serum PRL in all subjects; however, the highest increments, regardless of body mass index (BMI), were observed in control women (p <0.005). Measurements of PRL mitogenic activity on the Nb2 lymphoma cell bioassay revealed a significant increase in the bioactive/immunoreactive (B/I) ratio of PRL under basal and stimulated conditions in obese PCOS subjects (p <0.05). Mean fasting glucose/insulin and glucose/insulin-AUC ratios were significantly lower (p <0.001) in obese PCOS when compared with all other groups.

CONCLUSIONS

These data support the existence of low DA hypothalamic tone in PCOS women that is likely involved in the inappropriate LH and PRL secretion frequently seen in this syndrome. In addition, our results suggest changes in PRL bioactivity in obese PCOS that may play a role in the development of hyperinsulinemia; however, whether PRL has a functional significance in the development of the metabolic disturbances frequently seen in PCOS remains to be elucidated.