Prl, TSH, GH and LH responses to metoclopramide and breast-feeding in normal and hyperprolactinaemic women

Evidence that an altered prolactin release is consequent to abnormal ovarian activity in polycystic ovary syndrome

OBJECTIVE

To investigate whether endogenous dopaminergic activity is impaired in polycystic ovary syndrome (PCOS)-affected women and is normalized by medical ovariectomy.

PATIENTS

Women with PCOS untreated (n = 23) and treated for 3 months with GnRH analogue (GnRH-a) administration (n = 10) and normal cycling young women (n = 23) as controls.

INTERVENTIONS

Acute blockade of dopaminergic receptors by the IV administration of 5 mg of the dopaminergic receptor blocking agent sulpiride (sulpiride test) was performed 3 to 7 days after the initiation of spontaneous menses in cycling women or medroxyprogesterone acetate-induced menses in PCOS women. In PCOS women treated with GnRH-a administration (goserelin depot, 3.6 mg SC every 28 days), the sulpiride test was repeated 10 to 15 days after the third GnRH-a administration.

MAIN OUTCOME MEASURE

Basal PRL levels and PRL increase induced by sulpiride.

RESULTS

Basal PRL levels and the PRL response to sulpiride were increased in women with PCOS. In women with PCOS medical ovariectomy induced by GnRH-a administration reversed to normal both basal and sulpiride-stimulated PRL levels.

CONCLUSIONS

In women with PCOS the abnormal regulation of PRL and presumably of hypothalamic neurotransmitters controlling PRL secretion is not a primary alteration but it is likely dependent on abnormal ovarian functionality.

Control of prolactin secretion

1. Prolactin is a 21,500 Dalton single-chain polypeptide hormone but may occur in 50 kDa and 150 kDa molecular variants. 2. These large PRL variants may be secreted predominantly; this condition is termed "macroprolactinemia". It is characterized by high immunological and normal biological serum levels of prolactin, and lack of clinical symptoms of hyperprolactinemia. 3. The information on PRL is encoded on chromosome 6. Transcription can be enhanced and suppressed by a variety of hormonal factors. 4. PRL is secreted in a pulsatile fashion; it displays a circadian rhythm (with a maximum during sleep) and is stimulated by some amino acids. PRL also responds to mechanical stimulation of the breast. 5. PRL rises during pregnancy, and maintainance of hyperprolactinemia (and, thereby, physiological infertility) is dependent on the frequency and duration of breast feedings. 6. Hypothalamic regulation of prolactin mainly involves tonic inhibition via portal dopamine. The physiological importance of various stimulating factors present in the hypothalamus is still incompletely understood. In particular, there is still no place for TRH in PRL physiology. 7. PRL is released in response to stress; this response may be mediated by opioids. The low-estrogen, low-gonadotropin amenorrhea of endurance-training women is not mediated by prolactin, however. 8. Estrogens stimulate PRL gene transcription via at least two independent mechanisms. There are many clinical examples of this estrogen effect on prolactin serum levels, and also on the growth of prolactinomas. 9. Mild hyperprolactinemia remains an enigma which cannot satisfactorily be resolved by biochemical or radiological testing. The border between "normal" and "elevated" prolactin is ill-defined. The possibility of macroprolactinemia complicates this matter even further. 10. The number of drugs which suppress prolactin by acting on pituitary D2 receptors, and which are useful in the treatment of hyperprolactinemia, continues to increase. In the field of ergot alkaloids, parenteral application appears to be a logical solution to the problem of the high first-pass effect; in addition, this form of treatment is frequently better tolerated than the oral route. 11. Prolactinoma development is presently being studied employing molecular biological techniques; the question of whether tumorigenesis can be attributed to specific defects of gene regulation remains to be answered.

Age alters pulsatile prolactin release: influence of dopaminergic inhibition

To determine the effect of age on pulsatile prolactin secretion, we examined prolactin pulse characteristics by cluster analysis in healthy young and old male subjects during the day and night. Pulsatile prolactin secretion was identified in all subjects during the day and night, and prolactin pulse frequency remains stable with age. Younger subjects had a significantly higher prolactin pulse amplitude, area, and peak interval during the night compared with older subjects. In contrast, daytime prolactin pulse characteristics were similar in young and old subjects. Because the major neuroregulator of prolactin is dopamine and because normal aging has been reported to be associated with reductions in hypothalamic dopamine content and effect, we determined whether the mechanism of altered day-night prolactin pulsatile secretion was due to changes in dopaminergic tone. We examined endogenous prolactin secretion after administration of the dopamine antagonist metoclopramide. Metoclopramide significantly increased mean serum prolactin concentration and prolactin pulse height and amplitude in all subjects during the day and night. However, net prolactin pulse amplitude after metoclopramide stimulation at night was significantly higher in older subjects compared with younger subjects. We conclude that prolactin pulse amplitude is blunted in elderly men at night and that daytime pulsatile prolactin secretion is unaltered by age in normal men. The mechanism for this alteration of nighttime prolactin pulsatile secretion in elderly men may be due to age-associated changes in dopaminergic regulation.

Treatment of hirsutism in polycystic ovary syndrome with bromocriptine

The value of bromocriptine in the treatment of hirsutism in polycystic ovary syndrome (PCO) was assessed subjectively and photographically in a double-blind trial in 22 women studied for 1 year. Menstrual frequency was recorded. Circulating concentrations of oestradiol, oestrone, testosterone, androstenedione, and sex hormone binding globulin (SHBG) were determined before treatment and after 6 and 12 months therapy. On the same occasions gonadotrophin concentrations (mean of 24 samples) and their response to 100 micrograms LHRH were determined. No evidence was found to support a therapeutic role for bromocriptine in the treatment of hirsutism or menstrual regulation in PCO. No biochemical changes were seen specific to bromocriptine therapy.

The acute effects of a dopamine antagonist (domperidone) on luteinising hormone, follicule stimulating hormone, prolactin and thyrotrophin secretion in polycystic ovarian syndrome: differential effect of ovulation

An alteration of the hypothalamic dopaminergic regulation of LH secretion has been implicated in the abnormal LH secretion of polycystic ovarian syndrome (PCOS). To investigate this, the acute effect of dopamine (DA) receptor blockade on LH, FSH, PRL and TSH secretion was determined. No effect was observed on either LH or FSH secretion in the PCOS patients or in normal women and LH pulsatility appeared to be maintained. When the PCOS patients were divided into those who ovulated in the preceding cycle and those who were anovulatory, it was observed that the ovulatory patients had a normal PRL and TSH response; whereas in the anovulatory patients, the PRL rise was blunted and the TSH response was absent. We conclude that this study gives no evidence to support the hypothesis of altered hypothalamic DA regulation of LH secretion in PCOS. The lack of LH response to DA blockade suggests that a physiological role of DA in the control of LH secretion seems unlikely as determined under these experimental conditions. The differences in PRL and TRH response may reflect anovulation rather than a fundamental abnormality in PCOS.