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 pol ycystic ovary syndrome (PCOS). Methods. Our group evaluated he response of pituitary PRL, LH, FSH, and TSH to the administration of a single 10-mg oral dose of the dopamine (DA) rec eptor antagonist metoclopramide in lean (n = 7) and obese (n = 8) PCOS wome n and in 11 regularly cycling age- and weight-matched controls (six lean an d five obese). In addition, circulating PRL bioactivity was evaluated by it s mitogenic activity on a lymphoma cell bioassay. Results. Oral administration of metoclopramide resulted in a significant in crease in serum PRL in all subjects; however, the highest increments, regar dless of body mass index (BMI), were observed in control women (p <0.005). Measurements of PRL mitogenic activity on the Nb2 lymphoma cell bioassay re vealed a significant increase in the bioactive/ immunoreactive (B/I) ratio of PRL under basal and stimulated conditions in obese PCOS subjects (p <0.0 5), Mean fasting glucose/insulin and glucose/insulin-AUC ratios were signif icantly lower (p <0.001) in obese PCOS when compared with all other groups. Conclusions. These data support the existence of low DA hypothalamic tone i n PCOS women that is likely involved in the inappropriate LH and PRL secret ion frequently seen in this syndrome, In addition, our results suggest chan ges in PRL bioactivity in obese PCOS that may play a role in the developmen t of hyperinsulinemia; however, whether PRL has a functional significance i n the development of the metabolic disturbances frequently seen in PCOS rem ains to be elucidated. (C) 2000 IMSS, Published by Elsevier Science Inc.