The effects of ovariectomy and estrogen treatment on the dopamine inhibition of gonadotropin and prolactin release

Do the limits of serum prolactin in disconnection hyperprolactinaemia need re-definition? A study of 226 patients with histologically verified non-functioning pituitary macroadenoma

BACKGROUND

The differentiation of a pituitary non-functioning macroadenoma from a macroprolactinoma is important for planning appropriate therapy. Serum PRL levels have been suggested as a useful diagnostic indicator. However, values between 2500 and 8000 mU/l are a grey area and are currently associated with diagnostic uncertainty.

OBJECTIVE

We wished therefore, to investigate the serum PRL values in a large series of patients presenting with apparently non-functioning pituitary macroadenomas.

PATIENTS AND METHODS

All patients presenting to the Department of Endocrinology in Oxford with clinically non-functioning pituitary macroadenomas (later histologically verified) between 1990 and 2005 were studied. Information documented in the notes on the medications and on the presence of conditions capable of affecting the serum PRL levels at the time of blood sampling was also collected.

RESULTS

Two hundred and twenty-six patients were identified (median age at diagnosis 55 years, range 18-88 years; 146 males/80 females; 143 gonadotroph, 46 null cell, 25 plurihormonal and 12 silent ACTH adenomas). All tumours had suprasellar extension. At the time of blood sampling 41 subjects were taking medications capable of increasing serum PRL. Hyperprolactinaemia was found in 38.5% (87/226) of the patients. The median serum PRL values in the total group were 386 mU/l (range 16-3257) (males: median 299 mU/l, range 16-1560; females: median 572 mU/l, range 20-3257) and in those not taking drugs capable of increasing serum PRL 363 mU/l (range 16-2565) (males: median 299 mU/l, range 16-1560; females: median 572 mU/l, range 20-2565). Serum PRL < 2000 mU/l was found in 98.7% (223/226) of the total group and in 99.5% (184/185) of those not taking drugs. Among the three subjects with serum PRL > 2000 mU/l, two were taking oestrogen preparations.

CONCLUSIONS

Based on a large series of histologically confirmed cases, serum PRL > 2000 mU/l is almost never encountered in nonfunctioning pituitary macroadenomas. Values above this limit in the presence of a macroadenoma should not be surrounded by diagnostic uncertainty (after acromegaly or Cushing's disease have been excluded); a prolactinoma is the most likely diagnosis and a dopamine agonist should be considered as the treatment of choice.

Neuromodulation in polycystic ovary syndrome

Although central and peripheral factors have been implicated in the neuromodulation of GnRH in PCOS, there are no definitive or conclusive data to establish a primary causal role for any one factor. Because increased GnRH pulse frequency is at least a contributor to the secretion of excess LH and insufficient FSH that are the proximate cause of chronic anovulation in PCOS, strategies to slow the GnRH pulse generator are likely to promote ovulation in women with PCOS. Several pharmacologic agents, such as dopamine agonists and antagonists, have been tried, but the lack of consistent effects in women with PCOS limits their clinical utility. Current treatment strategies include the use of the combined oral contraceptive pills, antiandrogens or androgen receptor blockers, and insulin sensitizers. Oral contraceptive preparations are effective in suppressing ovarian hyperandrogenemia, regulating menstrual cycles, and reducing the risk of endometrial hyperplasia. Androgen blockade and antiandrogens provide symptomatic relief from androgen-induced acne and hirsutism and have been reported to restore ovulation in women with PCOS. Whether this effect is mediated peripherally or centrally remains to be clarified. The most recent class of pharmacologic agents to gain popularity are the "insulin modifiers." With increasing evidence that insulin resistance constitutes a key metabolic element, it seems logical that improving insulin sensitivity and glucose disposal might wholly, or partially, reverse certain features of PCOS, including anovulation. To date, insulin modifiers have proved most promising in improving the clinical features and promoting fertility, but whether this effect is centrally mediated is yet to be elucidated.

Induction of ovulation with clomiphene citrate in combination with metoclopramide in patients with amenorrhea of hypothalamic origin

Literature data have demonstrated that the chronic use of metoclopramide (MCP), a dopamine antagonist, causes increased gonadotropin secretion in patients with hypothalamic amenorrhea but without triggering ovulation. It has also been observed that women with hypothalamic amenorrhea respond poorly to ovulation induction with clomiphene citrate (CC). On this basis, the objective of the present study was to determine the effect of MCP on the response to CC in patients with hypothalamic amenorrhea in order to evaluate the validity of the simultaneous use of these drugs as ovulation inducers in this type of chronic anovulation. Twenty-two patients with amenorrhea of hypothalamic origin were submitted to a randomized double blind study in which one tablet of 5 mg MCP or placebo was administered every 8 hours for 2 months. After the 30th day of medication (MCP or placebo), CC, 100 mg orally, was additionally administered to both groups for 5 days. Blood samples were collected on days 1, 15 and 30 during the first month of the study and on days 7, 14 and 21 after the last CC tablet during the second month, for later measurement of follicle-stimulating hormone (FSH), luteinizing hormone (LH), prolactin, estradiol and progesterone by radioimmunoassay. The group that received MCP showed a significant increase in LH and FSH during the first month of the study, as well as a slighter increase in estradiol. Prolactin increased only during the second stage of treatment. No significant increases in gonadotropins, prolactin or estradiol occurred in the placebo group. In the group treated with MCP, 40% of the patients ovulated after CC, with menstruation occurring in 60% of them. In the placebo group, 33.3% of the women ovulated after CC and 44.4% menstruated at the end of the study. We conclude that MCP increases the circulating levels of LH, FSH, estradiol and prolactin in patients with hypothalamic amenorrhea and low estrogen levels, supporting the hypothesis that an increase in hypothalamic dopaminergic tonus occurs in these patients. On the other hand, the combination of MCP and CC does not improve the rate of ovulation compared to placebo.

Endogenous catecholamines augment the inhibitory effect of opioids on luteinizing hormone secretion during the midluteal phase

OBJECTIVE

Our purpose was to test the hypothesis that endogenous catecholamines may interact with endogenous opioid peptides to influence gonadotropin secretion during the midluteal phase in normal women.

STUDY DESIGN

Normal cycling women studied during the midluteal phase were randomized to one of four treatment groups: (1) alpha-methyl-para-tyrosine, (2) naloxone, (3) alpha-methyl-para-tyrosine and naloxone, and (4) control. Mean treatment luteinizing hormone levels were compared by analysis of variance. Pulse frequency, amplitude, and integrated area under the curve were assessed by CLUSTER analysis and compared by means of nonparametric analyses.

RESULTS

Mean luteinizing hormone levels were significantly higher in the naloxone and alpha-methyl-para-tyrosine plus naloxone groups compared with alpha-methyl-para-tyrosine or placebo. Coadministration of alpha-methyl-para-tyrosine and naloxone caused a significant increase in large-burst luteinizing hormone pulses compared with the group receiving naloxone only.

CONCLUSION

Endogenous catecholamines augment the inhibitory effect of opioids on luteinizing hormone secretion during the midluteal phase in normal cycling women.

Age-related changes in the metoclopramide-induced prolactin release in nulliparous women

OBJECTIVE

To assess the metoclopramide-stimulated PRL response in nulliparous women as a function of chronological age (CA).

DESIGN

Open and prospective study.

SETTING

Outpatient endocrine clinic of a third level medical institution.

PATIENTS

Fifty-one clinically healthy volunteer nulliparous women 15.8 to 48.2 years of age, with regular menses at least 1 year before the study (except 3 postmenopausal women) and no regular drug ingestion during the last 6 months, studied on days 18 to 22 of their menstrual cycle.

INTERVENTIONS

After a 30-minute rest, three basal blood samples were obtained; oral metoclopramide (10 mg) was administered followed by subsequent blood samples at 60, 90, and 120 minutes.

MAIN OUTCOME MEASURES

Duplicate serum PRL determinations were performed by RIA in all samples with P and E2 only in the pool of the basal samples. Hypothesis was formulated before data collection.

RESULTS

All menstruating women had serum P levels > or = 4.0 ng/mL (> or = 12.72 nmol/L). A linear correlation was observed between CA and the serum PRL response, and also between CA and serum E2. Multiple regression analysis showed that CA and body mass index had the most marked effect on PRL response. Women < or = 25.0 years old had a serum PRL response and mean basal serum E2 levels lower than women > 25.1 years old.

CONCLUSIONS

The metoclopramide-induced PRL response in nulliparous women augmented linearly as CA increased, suggesting a gradual decrease in the dopaminergic tone in older women, perhaps partially compensated by a high estrogen level to prevent an unrestrained rise in serum PRL levels.

Synchronous secretion of LH and prolactin during the normal menstrual cycle

Integrated hourly concentrations of day-time prolactin and LH showed significant positive correlations (p < 0.05-0.001) on the day of the pre-ovulatory mid cycle LH surge (n = 3) and during the mid luteal phase (n = 6) in a group of regularly cyclic women. No correlations between these two hormones were seen during any other stage of the cycle. Consistent significant correlations were not evident between prolactin and oestradiol, prolactin and progesterone, LH and oestradiol or LH and progesterone during any other stage of the cycle.

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.

Decrease of prolactin secretion via stimulation of pituitary dopamine D-2 receptors after application of talipexole and SND 919

The present experiments were performed to investigate the effects of talipexole (B-HT 920) and SND 919 on prolactin release from the anterior pituitary glands of rats both in vivo and in vitro. The basal serum prolactin levels were reduced dose dependently by s.c. administration of talipexole or SND 919 at doses of 5-100 micrograms/kg. Daily treatment with estradiol (35 micrograms/kg for 3 days) increased serum prolactin levels in male rats to levels 4-fold higher than those of non-primed rats. This increase was suppressed by administration of talipexole or SND 919. In vitro, the spontaneous prolactin release into perfusates from isolated anterior pituitary was inhibited by talipexole or SND 919 added at concentrations ranging from 10(-9) to 10(-6) M. This inhibitory effect of SND 919 was blocked by concurrent application of a dopamine D-2 receptor antagonist, YM-09151-2. The spontaneous prolactin release from the anterior pituitary isolated from estradiol-primed rats was 2-fold higher than that from non-primed rats. This increased release was also inhibited by application of either drug. The inhibitory effects of these drugs were greater in estradiol-primed rats than in non-primed rats when expressed as percent inhibition of control prolactin release. The results suggest that talipexole and SND 919 have a selective dopamine D-2 receptor agonistic property and are almost completely effective to counteract the enhancement of prolactin release induced by estrogens via stimulation of dopamine D-2 receptors in the anterior pituitary.

Plasma catecholamine metabolites and polycystic ovary syndrome

It has been postulated that catecholamine metabolism may be altered in cases of polycystic ovary syndrome. To search for possible correlations between catecholamine metabolism and hormonal disturbances, we have studied the serum LH, LH:FSH ratio, testosterone, and plasma catecholamine metabolites in patients with polycystic ovary syndrome and in control subjects with normal ovulatory cycles. The metabolites studied were 3-methoxy-4-hydroxyphenylglycol (MHPG) and 3,4-dihydroxyphenylacetic acid (DOPAC) as markers of adrenergic activity and dopaminergic activity, respectively. The polycystic ovary was divided into 2 patterns [general cystic pattern (GCP) and peripheral cystic pattern (PCP)] as determined by ultrasound. The results were as follows: 1) Serum LH, LH:FSH ratios, and plasma MHPG levels in patients with polycystic ovary syndrome were significantly higher than in the controls. 2) In cases of polycystic ovary syndrome, serum LH, LH:FSH ratios, and testosterone showed no significant correlations with catecholamine metabolites. 3) Using the ultrasonographical classification, we found that plasma MHPG levels of the GCP group were significantly higher compared with the PCP group in patients with polycystic ovary syndrome. Thus, catecholamine metabolism is altered in patients with polycystic ovary syndrome, and ultrasonography revealed different patterns of catecholamine metabolism.

Increased dopamine turnover in women with polycystic ovary syndrome

The main dopamine metabolite, homovanillic acid (HVA), was measured in urine samples from 35 women with polycystic ovary syndrome (PCO) and in 38 normal menstruating women of the same age range. In both groups the plasma levels of LH, FSH, prolactin and testosterone were also measured. HVA excretion was significantly increased in women with PCO. Plasma levels of LH correlated negatively (r = -0.6268, 2a less than 0.001) to urinary HVA in the group of normal women. This correlation did not exist in the women with PCO. The results suggest that there is a disturbance of the inhibitory influence of dopamine on LH secretion in women with the syndrome, which is not due to a deficient synthesis or utilization of dopamine.

Possible dopaminergic system involvement in LH and PRL responses to naltrexone treatment

Naltrexone (Nalt) causes a rapid increase in luteinizing hormone (LH) level. This short term increase of LH concentration declines to baseline levels in less than 1 hour. Addition of pimozide (0.1 mg) caused a blunted response to Nalt challenge, with significantly reduced LH peak values compared with Nalt treatment alone. Pimozide alone caused a delayed decrease compared with baseline LH values. By following plasma prolactin (PRL) levels it was shown that pimozide administration increased PRL levels rapidly for more than 2 hours. Addition of Nalt to pimozide-treated rats significantly decreased plasma PRL values compared with pimozide alone. Nalt injected by itself attenuated PRL baseline levels. Thus, the mechanism by which pimozide caused PRL elevated level is via the dopaminergic as well as the opioid system. It is suggested that the opioid system controls plasma PRL and LH levels through other hypothalamic neurotransmitters in addition to dopamine.

Low-dose dopamine infusions do not ablate luteinizing hormone pulses in women

The effect of dopamine on the secretion of luteinizing hormone in 15 euprolactinemic and 15 hyperprolactinemic women was investigated using infused doses of dopamine that achieved circulating levels from 2 to 100 times basal physiologic concentrations. The normal women were studied in the early follicular phase of the cycle. Different concentrations of dopamine were maintained at each dose level for 2 hours. Blood samples were obtained every 15 minutes and concentrations of dopamine, luteinizing hormone, follicle-stimulating hormone, and prolactin quantified. Mean basal concentrations of estradiol were 53 +/- 19 pg/ml in the euprolactinemic and 33 +/- 12 pg/ml in the hyperprolactinemic women; mean prolactin levels were 8.1 +/- 3.9 ng/ml in euprolactinemic and 183 +/- 174 ng/ml in hyperprolactinemic women; mean basal dopamine concentrations were 323 +/- 308 pg/ml in euprolactinemic and 337 +/- 232 pg/ml in hyperprolactinemic women. All doses of dopamine achieved some degree of prolactin suppression, but doses that achieved nanomolar circulating concentrations did not significantly affect luteinizing hormone secretion. Eight of the women in each group exhibited high-amplitude luteinizing hormone pulses, which persisted during the dopamine infusions. Neither the amplitude nor frequency of luteinizing hormone release correlated with basal estradiol, luteinizing hormone, or prolactin levels. We conclude that low doses of dopamine infused into the peripheral circulation do not achieve significant suppression of luteinizing hormone release. In some women during the early follicular phase of the menstrual cycle and in some amenorrheic hyperprolactinemic women, luteinizing hormone is secreted in a pulsatile manner characterized by high-amplitude low-frequency bursts. These bursts of luteinizing hormone were not influenced by elevations in circulating dopamine concentrations sufficient to suppress prolactin.

Prolactin secretion in polycystic ovary syndrome: circadian rhythmicity and dynamic aspects

The circadian rhythms of plasma prolactin (PRL) and cortisol and of oral temperature were simultaneously studied in 24 women with polycystic ovary syndrome (PCOS). The PRL response to thyrotropin-releasing hormone (TRH) and domperidone was also evaluated in some of these patients. The physiological circadian chrono-organization of prolactin and cortisol secretion and of oral temperature was maintained in PCOS. The PRL responsiveness to the specific stimulations fell within normal limits. These results do not support the hypothesis of an impaired central dopaminergic regulation of prolactin secretion in PCOS.

Opiate system involvement in the control of LH secretion in diabetic and normoglycemic male rats

The effect of Naltrexone (Nalt), a specific opiate receptor blocker, on LH secretion was studied at frequent intervals during the first hour following treatment. Nalt was injected i.v. by one bolus (1 mg/rat) to diabetic and normoglycemic rats. Blood samples (0.8 ml) were withdrawn at short intervals after injection, through an indwelling cannula. The diabetic rats responded by secretion of LH, which was lower, but not significantly, than that of normal rats, (peak levels 0.74 +/- 0.17 and 0.97 +/- 0.21 ng/ml respectively). After 45 min., LH levels were in the same range as baseline level in the diabetic group; but were still significantly elevated in the control rats. Thus, it can be concluded that in normal rats, as well as in diabetics, LH secretion as a response to Nalt was episodic in spite of Nalt's long half life time. In order to explain the rapid fall in LH levels after Nalt administration, normal rats were injected with a second bolus of Nalt, 2 hours after the first. The second bolus caused only a blunted response of LH secretion. In another experiment, administration of morphine (1 mg/rat) 2 hours after pretreatment with Nalt did not stimulate the prolactin secretion which normally follows morphine treatment. These results indicate that the rapid decrease of LH levels after Nalt treatment in normal rats is not due to absence of the drug in the system. It is suggested that other neural mechanisms, such as the dopaminergic system, are activated during Nalt influence.

Acute effects of L-dopa and bromocriptine on serum PRL, LH and FSH levels in patients with hyperprolactinemic and normoprolactinemic polycystic ovary syndrome

We have investigated the importance of the dopaminergic control of gonadotropin secretion by studying LH, FSH and PRL responses to L-dopa and bromocriptine in patients with polycystic ovary syndrome (PCOS). Both L-dopa and bromocriptine administration were followed by a statistically significant decrease in LH in the hyperprolactinemic PCO patients (compared to the normoprolactinemic subgroup - p less than 0.01 and control group - p less than 0.05); the decline was proportional to the basal level of LH. A significant positive correlation between basal LH levels and maximum net decrease of LH was observed after administration of both agents (p less than 0.01). Although both subgroups of PCO patients showed a similar decrease in PRL levels it was statistically significant only in the normoprolactinemic patients (p less than 0.01). Prolactin sensitivity to the inhibitory effect of bromocriptine and L-dopa showed a significant correlation with the basal PRL level (p less than 0.01). The response of serum FSH was variable and not significant. These results suggest that a reduction of an inhibitory influence of hypothalamic dopamine might be a cause of inappropriately elevated LH and PRL levels found in patients with polycystic ovary syndrome and hyperprolactinemia.

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.

Sex-related naloxone influence on growth hormone-releasing hormone-induced growth hormone secretion in normal subjects

The effect of opiate-receptor antagonist naloxone on growth hormone (GH) release after growth hormone-releasing hormone (GHRH) 1-44 administration was investigated in ten normal men and 18 normal women during different phases of their menstrual cycle. Naloxone was infused at a rate of 1.6 mg/h in women and 1.6- and 3.2 mg/h in men, starting one hour before GHRH administration (50 micrograms iv as a bolus). On different day sessions, naloxone, GHRH, or saline were administered as controls. Naloxone infusion reduced the GHRH-induced GH release in normal women. The mean % inhibition of peak GH response was 83% during follicular phase, 46.5% during periovulatory phase, and 77.6% during luteal phase. On the contrary, in normal men, both doses of naloxone infusion were ineffective in blunting the GH response to GHRH. Our studies indicate that naloxone infusion was capable of inhibiting GH release induced by direct stimulation with GHRH in normal women, suggesting an opiate-antagonist action at the anterior pituitary level. The absence of such an effect in normal men strongly indicates a sex dependence of naloxone effects and suggests a role of the sexual steroid environment in opioid modulation of pituitary hormone secretion.

Failure of prophylactic surgery to avert massive pituitary expansion in pregnancy

Macroprolactinomas have a well-recognized potential for marked expansion during pregnancy. Measures advocated to minimize this risk include prior treatment with dopamine agonists, radiotherapy and pituitary surgery. We describe a patient who underwent transsphenoidal surgery with the removal of an histologically proven prolactin-secreting adenoma with the intention of rendering subsequent pregnancy safe. The patient remained hyperprolactinaemic and received prolonged therapy with metergoline and bromocriptine which suppressed prolactin to normal and she conceived after induction of ovulation with human menopausal gonadotrophin and human chorionic gonadotrophin. At 3 months gestation she developed headaches, vomiting, reduced visual acuity and bitemporal hemianopia caused by massive pituitary expansion. Reintroduction of bromocriptine rapidly abolished features of tumour expansion and after delivery of a full-term normal female infant, repeat CT scan documented tumour shrinkage.

Further acquisitions on gonadal function in bromocriptine treated hyperprolactinemic male patients

The diurnal variation of plasma total and free testosterone (tT and fT) and the gonadotropinemic response to LH-RH were evaluated in a group of hyperprolactinemic impotent males with pituitary microprolactinoma before and during therapy with bromocriptine, a well known dopamine agonist drug. Before treatment, basal levels not only of tT but also of fT were decreased and the diurnal variation of both tT and fT was absent. Moreover, the LH-RH test showed a delay in the LH response peak, together with normal basal levels of LH. Bromocriptine therapy caused normalization of both the secretion response of LH to LH-RH and of the secretion pattern of tT and of fT (basal levels and diurnal variation) besides a significant decrease in PRL levels and an improvement in sexual function. The possible effects of high plasma levels of PRL at various levels of the hypothalamus-pituitary-testicular axis are discussed.

A relationship between gonadotropins and visuospatial function

Follicle Stimulating Hormone (FSH) levels were negatively correlated with visuospatial function in two successive testing sessions in 32 young adult men. Men with high concentrations of FSH performed poorly on three-dimensional tests and tests of point localization. Men with low concentrations tended to perform better. Luteinizing Hormone (LH) tended to correlate positively with verbal/sequential skills and with two of the visuospatial skills for one session; testosterone was positively correlated with one spatial test. Multiple regression between the average performance on visuospatial tests and the three hormones produced Rs of 0.67 and 0.60, accounting for 39% and 29% of the variance, respectively, in Sessions 1 and 2. In women, the hormonal/behavior relationships were less clear although in many ways similar. For example, FSH was negatively correlated with one visuospatial test but only after the effects of estradiol and progesterone were partialled out. FSH was positively correlated with word fluency as was LH. With respect to sex differences women were poorer than men on the visuospatial tests and better on verbal fluency which is consistent with women's generally higher FSH levels and the negative relationship between FSH and visuospatial skills and the positive relationship with fluency.

The influence of oestrogens on the sensitivity of PRL, TSH and LH to the inhibitory actions of dopamine in hyperprolactinaemic patients

The effects of oestrogen priming on the response of serum PRL, LH and TSH to dopamine (DA) infusion have been studied in hyperprolactinaemia. Seven hyperprolactinaemic females (aged 22-57 years; basal PRL 911-5130 mU/l, normal less than 420 mU/l), had submaximal DA infusions (0.06 micrograms/kg/min) over 3 h. The DA was repeated at the same dose after pretreatment with ethinyl oestradiol (E2) 100 micrograms daily by mouth for 3 d, and after a further 2 week interval, following pretreatment with tamoxifen (TAM) 20 mg twice a day by mouth for 3 d. Ethinyl oestradiol pretreatment stimulated a rise in basal PRL levels in all subjects (mean +/- SE, mU/l; 2903 +/- 761 vs 2293 +/- 684, P less than 0.05) while TAM produced a higher but more variable increase in basal PRL levels (mean +/- SE, mU/l; 3402 +/- 757, P = n.s.). The individual increments in basal PRL levels after both E2 and TAM pretreatment showed a significant positive correlation with the greater decrement in PRL levels during E2 and TAM primed DA infusions (E2, r = 0.93, P less than 0.01, TAM, r = 0.83, P less than 0.05). E2 pretreatment produced a rise in basal LH levels in 5/7 patients, and there was a significant positive correlation between the rise in basal LH levels after E2 and the decremental change in LH levels in E2 primed DA infusions (r = 0.94, P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Dopamine decreases release of luteinizing hormone releasing hormone from superfused rat mediobasal hypothalamus

The effects of dopamine hydrochloride (DA) on the releases of LHRH and LH were examined in a serial sequential double chamber perifusion system by perifusing the mediobasal hypothalamus including the preoptic area and/or pituitaries excised from diestrus female rats. DA, perifused at a dose of 4.2 X 10(-4) M, significantly (p less than 0.05) lowered LH secretion from the pituitary in series with the hypothalamus 40-80% below the preinfusion level, but it had no effect on LH efflux from the pituitary perifused alone. DA also significantly (p less than 0.05) reduced the LHRH level 20-40% below the initial level. Perifusion with the DA receptor blocker haloperidol at a concentration of 10(-6) M abolished the suppressive effect of DA on LH secretion. These findings indicate that DA suppressed hypothalamic LHRH release, resulting in decrease in LH secretion from the pituitary in diestrus rats.

Effect of low-dose dopamine infusion on basal and stimulated TSH and prolactin concentrations in man

Dopamine (DA) infused at pharmacological doses in man inhibits thyrotrophin (TSH) secretion, although the physiological significance of this observation is unclear. The effect of low-dose DA infusion (0.1 microgram/kg/min) on TSH and prolactin (PRL) concentrations during stimulation with thyrotrophin releasing hormone (TRH) in normal male subjects is reported. Six subjects were given intravenous DA or placebo infusions for 165 min on separate days. A bolus of TRH (7.5 micrograms) was given at + 90 min, followed by infusion of the tripeptide (750 ng/min) for 45 min during both DA and placebo studies. In all subjects TRH administration caused a small rise in TSH which was partially inhibited by DA (peak 5.73 +/- 0.85 mU/l vs 4.58 +/- 1.09, P less than 0.05). PRL response to TRH was almost totally inhibited by DA (620 +/- 164 mU/l vs 234 +/- 96, P less than 0.05); integrated TSH and PRL responses to TRH were similarly inhibited by DA. Circulating plasma DA concentration during infusion of the catecholamine was 3.46 +/- 1.00 ng/ml, which is within the range reported in pituitary stalk plasma of other species. These data support the hypothesis that DA is a physiological modulator of TSH secretion in normal man. Major differences in the time course of TSH and PRL responses to TRH, and in the suppressive effect of DA on these responses suggest that there are fundamental differences in stimulus-secretion coupling for TRH and the lactotroph and thyrotroph.

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.

The influence of gonadal steroids on the dopamine inhibitory effect on gonadotropin release in men

The aim of this study was to ascertain whether an interrelationship exists between gonadal steroids and the inhibition of gonadotropin secretion by dopamine. The effect of dopamine infusion (4 micrograms/kg/minute intravenously) on gonadotropin plasma levels in four castrated men (18 to 23 years of age) and in four age-matched normal men was studied. Normal subjects were studied before and after treatment with a specific nonsteroidal estrogen receptor antagonist, CC. LH plasma levels in normal subjects receiving CC had a maximum decrease percentage and a net decrease significantly greater (P less than 0.005 and P less than 0.012, respectively) than those before CC treatment. In castrated subjects the maximum decrease percentage was significantly greater (P less than 0.005) than in control subjects, but it did not show any difference from that of normal subjects receiving CC. In none of the group were significant changes in FSH concentration observed. The findings suggest that whenever there is a gonadal steroid deficiency, dopamine infusion causes an increased sensitivity to LH inhibition. This may be due to a lower endogenous dopaminergic influence on LH secretion.

Evidence for altered catecholamine metabolism in polycystic ovary syndrome

It has been hypothesized by Yen et al. that there is decreased dopaminergic control of luteinizing hormone secretion in polycystic ovary syndrome. Levels of urinary homovanillic acid, dihydroxyphenyl acetic acid, and 3-methoxy-4-hydroxyphenylglycol were measured in seven women with polycystic ovary syndrome and in six matched control subjects to reflect, in part, central dopamine and norepinephrine metabolism. In addition, gonadotropin-releasing hormone stimulation tests were carried out in women with polycystic ovary syndrome and in control subjects. In patients with polycystic ovary syndrome, serum gonadotropin levels were determined before and after gonadotropin-releasing hormone stimulation, before and after treatment with 500 mg of L-dopa for 1 week, and again before and after treatment with 400 mg of L-dopa and 100 mg of carbidopa for 1 week the following month. Urinary homovanillic acid and dihydroxyphenyl acetic acid levels were significantly lower and the level of 3-methoxy-4-hydroxyphenylglycol was significantly higher in patients with polycystic ovary syndrome (p less than 0.05). There was a significant negative correlation between levels of homovanillic acid and serum luteinizing hormone (r = -0.57, p less than 0.05) and a positive correlation between the ratio of 3-methoxy-4-hydroxyphenylglycol/homovanillic acid and luteinizing hormone (r = 0.75, p less than 0.01). After gonadotropin-releasing hormone stimulation, delta max serum luteinizing hormone was elevated in patients with polycystic ovary syndrome but decreased to control levels after treatment with L-dopa. No changes occurred in baseline levels of serum luteinizing hormone or follicle-stimulating hormone. After treatment with L-dopa-carbidopa, baseline levels of luteinizing hormone and follicle-stimulating hormone were unchanged as were responses after gonadotropin-releasing hormone stimulation. These data suggest that there may be altered catecholamine metabolism in polycystic ovary syndrome. Viewed together with previous findings by Yen et al., our data support the hypothesis that there is decreased dopaminergic control of luteinizing hormone in polycystic ovary syndrome.

Evidence for decreased endogenous dopamine and opioid inhibitory influences on LH secretion in polycystic ovary syndrome

The inhibitory role of the dopaminergic and opioidergic mechanisms in the control of LH secretion in patients with polycystic ovary syndrome (PCO) was evaluated. The administration of an opiate receptor antagonist, naloxone, of a dopamine receptor antagonist, metoclopramide, or of human synthetic beta h-endorphin, were unable to alter LH secretory activity in patients with PCO. Since identical doses of these antagonists and the opiate agonist have elicited respectively a rise and fall of LH levels in normal cycling women, these findings suggest that an underlying hypothalamic component of defect in endogenous dopamine and opioid control may be responsible for the inappropriate gonadotrophin secretion in this syndrome.

Clinical evaluation of the effects of combined treatment with bromocriptine and spironolactone in two women with the polycystic ovary syndrome

Two women with the polycystic ovary syndrome were treated with bromocriptine (15 to 20 mg/day) in combination with spironolactone (100 mg/day). In the first woman the combined therapy induced a marked reduction of hirsutism, with ensuing ovulation and pregnancy. In the second woman, who had hyperthecosis and had been refractory to treatment with clomiphene and wedge resection, the combined therapy resulted in abolition of hirsutism, normalization of blood pressure, weight reduction, and improvement in glucose intolerance. In this patient fertility could not be established by the above treatment, but the symptomatic amelioration was so great that she accepted no further attempt to induce ovulation. In view of the marked amelioration of the polycystic ovary syndrome induced by combined bromocriptine and spironolactone treatment, this mode of therapy should receive further consideration.

Amplification of LH response to LHRH by dopamine infusion in eugonadal women

Although the role of biogenic amines in the regulation of gonadotropin release has been studied extensively, the precise role of dopamine (DA) in stimulating LHRH and/or LH release is still controversial. In the present study 6 eugonadal women, aged 20-30, were given an LHRH infusion on day 6 of the menstrual cycle and the pattern and magnitude of LH and FSH responses were estimated. On day 6 of the next cycle, the experiment was repeated and DA was also infused beginning 60 min after the start of the LHRH infusion. Following LHRH infusion plasma LH showed a marked and significant rise with a mean peak increment at 4 h, and with a cumulative response (CR) of 9136 +/- 955 mIU/ml/6h. The pattern of FSH response tended to parallel that of LH; however, mean peak increment at 4 h and a CR of 2640 +/- 169 mIU/ml/6h were markedly lower. Plasma prolactin levels remained unchanged. Addition of DA to LHRH at 60 min evoked a significantly greater mean peak LH increment at 4 h and a CR of 15514 +/- 1836 mIU/ml/6h (p less than 0.001). There were no significant changes in either mean FSH peak at 4 h or in the CR (3257 +/- 309 mIU/ml/6h). As expected, a highly significant (p less than 0.001) decrease in circulating PRL from 12.1 +/- 3.1 to 3.0 +/- 1.5 ng/ml was seen during DA infusion. In conclusion, DA given by iv infusion enhancement LH response to LHRH in eugonadal women under the conditions of the present investigation, supporting a role for a dopaminergic component in the control of LH release in women.

Abnormal catecholamine mechanisms in hypothalamic-pituitary disorders

Patients with growth hormone or prolactin-secreting pituitary tumors failed to show normal plasma catecholamine (especially norepinephrine) responses to oral bromocriptine. These patients had normal basal plasma catecholamine concentrations. Patients with anorexia nervosa had low basal levels of dopamine, norepinephrine, and epinephrine. These data are consistent with disordered catecholamine metabolism in patients with these neuroendocrine disorders.