Effect of the dopamine agonist, lergotrile mesylate, on circulating anterior pituitary hormones in man

Oral glucose load and mixed meal feeding lowers testosterone levels in healthy eugonadal men

PURPOSE

Precise evaluation of serum testosterone levels is important in making an accurate diagnosis of androgen deficiency. Recent practice guidelines on male androgen deficiency recommend that testosterone be measured in the morning while fasting. Although there is ample evidence regarding morning measurement of testosterone, studies that evaluated the effect of glucose load or meals were limited by inclusion of hypogonadal or diabetic men, and measurement of testosterone was not performed using mass spectrometry.

METHODS

Sixty men (23-97 years) without pre-diabetes or diabetes who had normal total testosterone (TT) levels underwent either an oral glucose tolerance test (OGTT) or a mixed meal tolerance test (MMTT) after an overnight fast. Serum samples were collected before and at regular intervals for 2 h (OGTT cohort) or 3 h (MMTT cohort). TT was measured by LC-MS/MS. LH and prolactin were also measured.

RESULTS

TT decreased after a glucose load (mean drop at nadir = 100 ng/dL) and after a mixed meal (drop at nadir = 123 ng/dL). Approximately 11% of men undergoing OGTT and 56% undergoing MMTT experienced a transient decrease in TT below 300 ng/dL, the lower normal limit. Testosterone started declining 20 min into the tests, with average maximum decline at 60 min. Most men still had TT lower than baseline at 120 min. This effect was independent of changes in LH or prolactin.

CONCLUSION

A glucose load or a mixed meal transiently, but significantly, lowers TT levels in healthy, non-diabetic eugonadal men. These findings support the recommendations that measurement of serum testosterone to diagnose androgen deficiency should be performed while fasting.

Pituitary function and the somatotrophic system in patients with idiopathic Parkinson's disease under chronic dopaminergic therapy

Idiopathic Parkinson's disease and dopaminergic medication may influence pituitary hormone secretion. The present study aimed to reveal any abnormalities of the somatotrophic system induced by the disease itself and/or the dopaminergic therapy. Investigations of other pituitary hormones under basal and stimulated conditions, as well as an analysis of body composition, were also performed. This was a controlled diagnostic study in which luteinising hormone-releasing hormone, thyroid-releasing hormone, corticotrophin-releasing hormone and arginine hydrochloride were administered to ten patients with idiopathic Parkinson's disease under dopaminergic medication. Basal and stimulated hormone concentrations and bioelectrical impedance analyses were compared with those of healthy, age-matched controls. Basal growth hormone (GH) at -30 and 0 min was higher in Parkinsonian patients (2.74 +/- 3.79 ng/ml versus 0.53 +/- 0.10 ng/ml and 2.12 +/- 2.44 ng/ml versus 0.51 +/- 0.03 ng/ml; P < 0.05). The area under the GH curve after stimulation was greater in Parkinsonian patients (502.4 +/- 202.6 ng x min/ml versus 312.0 +/- 98.5 ng x min/ml; P < 0.05), depending on higher basal GH levels, rather than a greater arginine response. No differences in insulin growth factor (IGF)-1 or IGF-BP3 concentrations were detected. There were no differences between the groups in basal and stimulated gonadotrophic, corticotrophic and thyrotrophic function, or body composition. Prolactin was below the detection limit in the patients during the course of the study. Parkinsonian patients experience marked hypoprolactinaemia and repeated stimulation of GH secretion during chronic dopaminergic therapy. Our findings suggest a peripheral GH resistance in these chronically-treated patients.

Drugs and HPA axis

This paper outlines the interferences of the most widely used drugs with hypothalamo-pituitary-adrenal function and the related laboratory parameters, with the purpose of providing practical help to clinicians during testing for hypo- or hypercortisolemic states.

A dose rising study of the safety and effects on serum prolactin of SK&F 101468, a novel dopamine D2-receptor agonist

1. SK&F 101468, a non phenolic indolone derivative, has been characterised preclinically as a novel, potent and specific dopamine D2-receptor agonist. 2. Its tolerability and effects on serum prolactin were investigated in 14 healthy male volunteers in a study of the first administration of SK&F 101468 to man. 3. Doses between 80 micrograms and 2.5 mg caused statistically significant (P less than 0.05) lowering of basal and food stimulated serum prolactin, relative to placebo, over a 6 h post treatment period. 4. SK&F 101468 was well tolerated up to 1 mg with symptoms of nausea and postural hypotension at higher doses.

TRH: behavioral and endocrine effects in man

1. The tripeptide TRH exerts a spectrum of biological activities in both animals and man. Some of these activities have been extensively studied, particularly in psychiatric patients. 2. Behaviorally, TRH appears to increase the sense of well-being, motivation, relaxation, and coping capacity in both normal subjects and patients with psychiatric and neurologic disease. These effects are not disease-specific; attempts to use TRH as a treatment tool have thus been disappointing. 3. Endocrinologically, administration of TRH stimulates the response of TSH; this response has been reported to be blunted in approximately 30% of patients with major depression. However, TSH blunting is not specific for depression, it has also been observed in a variety of other psychiatric conditions. 4. The relevance of these effects for psychiatry in general, and for psychoneuroendocrinology especially, is discussed in this review.

Differential action of bromocriptine on nigrostriatal versus mesolimbic dopaminergic neurons

The present study was undertaken to compare the abilities of the dopaminergic agonists apomorphine, bromocriptine, and lergotrile to inhibit the synthesis of dopamine (DA) in terminals of nigrostriatal and mesolimbic DA neurons. The in vivo synthesis of DA was estimated by measuring the rate of accumulation of dihydroxyphenylalanine (DOPA) in terminals of nigrostriatal (striatum) and mesolimbic (nucleus accumbens, olfactory tubercle) neurons 30 min after the administration of NSD 1015, a decarboxylase inhibitor. The activation of DA autoreceptors in these regions was evaluated by measuring the abilities of the DA agonists to inhibit DA synthesis in brain regions of rats pretreated with gamma-butyrolactone (GBL). Apomorphine (0.03-1.0 mg/kg for 45 min) and bromocriptine (0.1-10 mg/kg for 90 min) produced dose-dependent decreases in the rate of DA synthesis in all three brain regions of both vehicle- and GBL-treated rats. A time course of the effects of the highest dose of bromocriptine (10 mg/kg), however, demonstrated dramatic regional differences in the ability of this drug to inhibit DA synthesis in saline-versus GBL-pretreated rats. Bromocriptine inhibited the GBL-induced increase in DA synthesis for 6 hours in all regions examined. In the striatum of saline-treated rats the decrease in DA synthesis was evident only at 1.5 hours after bromocriptine administration, while in the nucleus accumbens and olfactory tubercle DA synthesis remained inhibited for 6 hours. By contrast, lergotrile reduced DA synthesis to a similar extent in all three regions for at least 6 hours in both vehicle- and GBL-treated rats. These results suggest that there is no regional difference in the ability of bromocriptine to inhibit DA synthesis via DA autoreceptor mechanisms, but there appear to be differences in postsynaptic DA receptor-mediated mechanisms which regulate nigrostriatal versus mesolimbic DA neurons.

Variability and selectivity of anterior pituitary response to dopamine agonists throughout the normal menstrual cycle

To clarify whether there is a variation of dopamine effect throughout the normal menstrual cycle, 24 studies were performed during the follicular, periovulatory, and luteal phase in seven ovulatory women. The subjects were studied for 24 hours after receiving two different dopamine agonists, 2.5 mg of bromocriptine in one cycle and 50 micrograms of pergolide in a subsequent cycle. Baseline plasma luteinizing hormone, follicle-stimulating hormone, prolactin, and thyrotropin were followed through time, and the dynamic responses to gonadotropin-releasing hormone and thyrotropin-releasing hormone before and at 6 and 22 hours after medication were studied. Since the results obtained with both agonists were similar, the data have been combined in a single group. Baseline luteinizing hormone levels (but not follicle-stimulating hormone) were significantly suppressed (p less than 0.01) during the follicular phase only, and the plasma luteinizing hormone and follicle-stimulating hormone response to gonadotropin-releasing hormone was not affected by the agonists in any of the three cycle phases. Baseline plasma prolactin was suppressed equally (p less than 0.005) in all phases of the cycle, and the response to thyrotropin-releasing hormone was similarly suppressed in all phases only at 6 hours (p less than 0.002). Baseline thyrotropin also was suppressed (p less than 0.01) in all phases but the degree of inhibition was greater in the luteal than in the follicular phase (p less than 0.05). The response to thyrotropin-releasing hormone was inhibited, with the smallest response seen at 22 hours (p less than 0.01). In conclusion, these results suggest that the modulatory effect of dopamine on pituitary hormone secretion is variable and selective throughout the normal menstrual cycle. The greatest inhibition is on prolactin release, which is similar in all phases, followed by thyrotropin, which is greater in the luteal phase, and then by luteinizing hormone in the follicular phase only; it has no effect on follicle-stimulating hormone release.

The TRH test during dopamine receptor blockade in depressed patients

In an evaluation of the possible role of dopamine on TRH test results, 21 depressed patients were given TRH before and after one week of treatment with a low dose of haloperidol. Haloperidol significantly increased serum prolactin (both basal and after TRH) and cortisol levels, decreased body temperature, and had no effect on serum TSH, growth hormone, or thyroid hormone levels. Five of six patients with initial TSH blunting were retested with TRH; in four patients the TSH response remained blunted. These data render it unlikely that dopamine exerts a major inhibitory input on TSH secretion in depression.

The effect of a new ergoline derivative, CU 32-085, in the treatment of acromegaly. A controlled study

The effect of a new dopamine agonist, CU 32-085 (8 alpha-amino-ergoline), on pituitary function in acromegaly was evaluated by a controlled, single blind study of 12 acromegalics. The study included a single dose placebo/drug (0.5 mg CU 32-085) trial and a long-term crossover trial with 3 month periods (placebo/CU 32-085 8 mg daily). The patients were evaluated clinically and biochemically (oral glucose tolerance (OGTT), TRH- and LHRH-tests) before and after each 3 month period. Nine patients completed this long-term trial; one died from myocardial infarction during the placebo period, and two dropped out because of side effects. The release of GH, judged from more than 9 h suppression of serum GH following the single dose, and from the response to OGTT after the long-term treatment, was significantly inhibited by CU 32-085. Serum GH reached normal values in 4 of 9 patients. Serum PRL was also markedly suppressed, to subnormal values after the 3 months in all but one hyperprolactinemic patient. Serum TSH, cortisol, FSH and LH were generally unaffected. Glucose tolerance was not significantly altered, although an improvement was found in six of nine patients. A semiquantitative evaluation of subjective symptoms showed a significant improvement following the long-term treatment, while objective signs of acromegaly were unaffected. The blood pressure was slightly lowered, both after a single dose and after 3 months' treatment. Seven patients experienced nausea and dizziness, two of them with vomiting, after a single dose of the drug. Four of these had similar symptoms initially during the long-term treatment, which forced two to interrupt the trial. We conclude that CU 32-085 caused a marked suppression of the release of GH and PRL and an improvement of the major symptoms of acromegaly, a therapeutic effect that is comparable to the previous experience with bromocriptine.

Plasma ACTH levels in depression before and after recovery: relationship to the dexamethasone suppression test

Sixteen patients with major depressive disorder who were nonsuppressors on the dexamethasone suppression test (DST) on hospital admission were studied for plasma levels of adrenocorticotropic hormone (ACTH). Eight patients reverted to normal suppression with clinical recovery, while eight remained nonsuppressors. There was a significant reduction of ACTH levels in those who normalized on their DST, while ACTH levels remained high in the group that continued to be nonsuppressors. The results favored the hypothesis that dexamethasone nonsuppression in depression is mediated by high ACTH levels.

Growth hormone neuroregulation and the clinical relevance of somatostatin

The hypothalamus controls GH secretion from the anterior pituitary using two peptides; somatostatin inhibits GH, but physiologically the most important appears to GHRF, the structure of which has recently been discovered by two groups. This exciting development has not only given us further insight into the control of GH secretion, but also posed interesting questions as to the cause of the abnormal GH responses to various stimuli seen in patients with acromegaly. The other hypothalamic peptide controlling GH secretion, somatostatin has been the subject of intensive research in the last ten years. It is widely distributed and has important physiological actions including those involved in GH secretion and its action as a hypothalamic hormone. The secretion and synthesis of these two hypothalamic hormones is in turn modulated by a number of neurotransmitters, the most important of which appears to be dopamine. Knowledge gained in these studies has enabled the development of useful tools in the diagnosis of growth hormone deficiency as well as the only effective medical treatment for acromegaly. Much remains to be learnt of the physiology of growth hormone releasing factor and as a result further patients will benefit in the future.

Relationship of changes in serum concentrations of prolactin and testosterone during dopaminergic modulation in males

To evaluate the effect of PRL on the male pituitary-gonadal system, serum concentrations of PRL, testosterone, LH and FSH were determined in healthy young men daily before, during, and after 3-day oral administration of bromocriptine, metoclopramide or sulpiride. Bromocriptine (2.5 mg as a single dose) caused, concurrently with a marked suppression of serum PRL, a significant increase of serum testosterone and a transient decrease of serum LH. The changes of PRL and testosterone were negatively correlated. With metoclopramide (10 mg q.i.d.) serum PRL was increased and testosterone inversely decreased. There was no change in LH and FSH. Sulpiride (50 mg q.i.d.) evoked the elevation of serum PRL and LH, but no change in testosterone. A significant increase in serum concentration of testosterone was also observed in a patient with PRL-producing pituitary tumour and four out of seven patients with acromegaly during bromocriptine treatment. These results suggest an inhibitory effect of PRL on testosterone secretion at the gonadal level, or direct dopaminergic stimulatory control of testosterone secretion.

Studies off the opiate control of prolactin, GH and TSH

Opiate peptides are known to influence the secretion of several anterior pituitary hormones under basal conditions. Further studies on prolactin, GH and TSH have therefore been performed in normal subjects, under basal and stimulated conditions, using an opiate agonist and antagonist. Sixteen mg naloxone had no effect on the basal release of prolactin or GH, but lowered TSH. An infusion of the met-enkephalin analogue DAMME (1 mg) increased GH, and produced an exaggerated response of both prolactin and TSH to 200 micrograms TRH i.v. The peak responses of both prolactin and GH to hypoglycaemia were unaffected by pretreatment with either low-dose (0.4 mg) or high-dose (25 mg) naloxone, or DAMME (0.25 mg). These results suggest that opiate peptides are unlikely to play a major role in the tonic or hypoglycaemia-stimulated release of prolactin and GH, although they may be of importance in the control of TSH.

Pituitary function in normoprolactinaemic infertile men receiving bromocriptine

A double blind trial of bromocriptine 7.5 mg daily versus placebo was carried out in ten infertile men. Pretreatment basal plasma prolactin, thyroid stimulating hormone (TSH) testosterone and luteinizing hormone (LH) concentrations were normal, but plasma follicle-stimulating-hormone (FSH) was raised in four individuals. After 4 months treatment with bromocriptine a significant fall in plasma prolactin was observed (P less than 0.01), both under basal conditions and following thyroid stimulating hormone releasing hormone (TRH). Basal plasma gonadotrophin, testosterone and thyroid stimulating hormone (TSH) concentrations did not alter. No change in sperm density, volume or motility was noted. However an apparent fall in the peak plasma LH (but not FSH) response to gonadotrophin releasing hormone (LHRH) was observed in patients receiving bromocriptine. This reduction in plasma LH responsiveness was significant when compared with the baseline response (P less than 0.05) but failed to reach significance when compared with the placebo response. It is concluded that prolonged bromocriptine therapy in normoprolactinaemic men does not suppress FSH secretion, and any reduction in plasma LH responsiveness to LHRH is not accompanied by a significant fall in plasma testosterone.

Neuroendocrine tests of monoamine function in man: a review of basic theory and its application to the study of depressive illness

Neuroendocrine tests are now available for studying monoamine function in the brains of patients with mental illness. Great care is required in the selection of drugs which act upon specific monoamine receptors to produce specific hormonal responses. Equal care is required in the control of biological variables which may influence hormonal release. Recently reported neuroendocrine studies of depressive illness are assessed in these terms. The results of these studies support the hypothesis that there is defective noradrenergic function in the brains of some patients with depressive illness.

Pharmacologic effects in man of a potent, long-acting dopamine receptor agonist

Single-dose administration of pergolide mesylate (100 to 400 micrograms) results in a dose-related inhibition of prolactin secretion which persists for more than 24 hours. During multiple-dose administration of pergolide, plasma prolactin concentrations remain markedly reduced (greater than 80 percnet) and gradually return to control levels several days after drug administration is discontinued.

The effect of lisuride hydrogen maleate, an ergot derivative on anterior pituitary hormone secretion in man

The effects of single oral doses of 0.2 mg of lisuride hydrogen maleate, a semisynthetic ergot derivative, on serum levels of prolactin (PRL), growth hormone (GH), thyroid stimulating hormone (TSH), luteinizing hormone (LH), follicle stimulating hormone (FSH), cortisol and blood glucose were studied in six normal males. Lisuride effectively inhibited basal PRL secretion as well as the PRL response to TRH given 3 h later. In addition, the drug raised basal GH levels and decreased basal and TRH stimulated TSH secretion. No significant differences between lisuride and control were observed in basal LH and FSH, LHRH stimulated gonadotrophins or in cortisol. Drowsiness was noted by all subjects, one became nauseated and another vomited, 60 and 90 min respectively after administration of lisuride. No changes were seen in pulse rate and blood pressure. The endocrine effects of lisuride were attenuated by the prior administration of the dopamine antagonist metoclopramide. These results suggest that lisuride acts as a long-acting dopamine agonist and that therefore this drug could be of therapeutic use in hyperprolactinaemic states and acromegaly.

The effects of dopamine, bromocriptine, lergotrile and metoclopramide on prolactin release from continuously perfused columns of isolated rat pituitary cells

The control of secretion of prolactin was studied using continuous perfusion of a column of isolated rat pituitary cells supported by Bio-Gel polyacrylamide beads. Prolactin secretion was inhibited repeatedly by dopamine and rapidly recovered in its absence. Maximum inhibition was achieved at 5 x 10(-7) M dopamine. Bromocriptine and lergotrile directly inhibited prolactin release from the pituitary cells. Bromocriptine had a longterm action in inhibiting secretion. The dopamine receptor blocking agent, metoclopramide, overcame the inhibitory effect of dopamine but had no effect on prolactin secretion in its absence.