Effect of the ergot derivative lisuride hydrogen maleate on serum prolactin concentrations in female rats

Dopamine Agonists: From the 1970s to Today

The discovery of dopamine inhibitory effects on prolactin secretion has led to an era of successful dopaminergic therapy for prolactinomas. Herein we provide an overview of the evolution of dopamine agonists and their use in patients with PRL-secreting pituitary tumors, starting from the 1970s up to today, highlighting that normalization of PRL levels, restoration of eugonadism, and reduction of tumor mass can be achieved in the majority of patients by treatment with dopamine agonists.

Influence of ergot derivatives on prolactin secretion in rats. Mechanisms of action and clinical implications

Ergot derivatives are the most effective compounds in the treatment of migraine attacks. It has been proposed that these compounds exert this effect by direct action on skull arteries or arteriovenous anastomoses, or by interfering with peripheral or central serotonin receptors. It is also possible that these compounds influence monoaminergic neurotransmission and, thereby, endorphines modulating the threshold for pain or sensory perception. In testing these hypotheses, changes in receptor sensitivity or function have to be considered since we have observed simultaneous tolerance and supersensitivity development in the same animal treated chronically with lisuride. We therefore propose that ergot derivatives can reduce the well documented higher sensitivity of migraine sufferers to various stimuli. In humans, prolactin-levels can be used for determining bioavailability of some ergot derivatives and for studying whether dopaminergic mechanism plays a role in their antimigraine effect.

Les dérivés de l'ergot sont les composés les plus efficaces dans le traitement des attaques de migraine. Il semble que ces composés exercent cet effet par une action directe sur les artères du crâne ou sur les anastomoses des artères, ou en interférant par les récepteurs sérotonine regiques periphériques ou centraux. Ces composés peuvent aussi influencer la neuro-transmission mono-aminergique et, par conséquent, donner lieu, par exemple, au phénomène des endorphines règlant le seuil de la douleur ou de la perception sensorielle. Lors de l'évaluation de cette hypothèse, il faut tenir compte des modifications de la fonction ou de la sensibilité des récepteurs car l'on a observé un développement simultané de la tolérance et de l'hyper-sensibilité même chez les animaux traités par lisuride pour des formes chroniques. Nous avons donc formulé l'hypothèse selon laquelles les dérivés de l'ergot peuvent réduire l'hyper-sensibilité à différents stimuli chez les personnes souffrant de migraines. Chez l'homme, les niveaux de prolactine peuvent être employés pour déterminer la disponibilité biologique de quelques dérivés de l'ergot ou pour vérifier un rôle possible du mécanisme dopaminergique dans leur effet anti-migraine.

I derivati dell'ergot sono i composti piu’ efficaci nel trattamento sintomatico e preventivo dell'emicrania; l'effeto sembra esercitarsi mediante un'azione diretta sulle arterie del cranio o sulle anastomosi arterovenose, oppure interferendo con i recettori serotoninergici periferici o centrali. E’ anche possibile che questi composti influenzino la neurotrasmissione endorfinergica della soglia del dolore o la sua percezione. Nel valutare queste ipotesi devono essere tenute in considerazione le variazioni funzionali e di sensibilita’ recettoriale, poichè noi abbiamo osservato uno sviluppo simultaneo della tolleranza e della supersensibilità negli stessi animali trattati cronicamente con lisuride. Abbiamo quindi formulato l'ipotesi che i derivati dell'ergot possono ridurre la ben nota maggiore sensibilata’ degli emicranici a vari stimoli. Nell'uomo i livelli di prolattina possono essere usati per determinari la biodisponibilita’ di alcuni derivati dell'ergot oppure per studiare se il meccanismo dopaminergico gioca un ruolo nel loro effetto anti-emicranico.

Medical treatment of prolactinomas

Prolactinomas, the most prevalent type of neuroendocrine disease, account for approximately 40% of all pituitary adenomas. The most important clinical problems associated with prolactinomas are hypogonadism, infertility and hyposexuality. In patients with macroprolactinomas, mass effects, including visual field defects, headaches and neurological disturbances, can also occur. The objectives of therapy are normalization of prolactin levels, to restore eugonadism, and reduction of tumor mass, both of which can be achieved in the majority of patients by treatment with dopamine agonists. Given their association with minimal morbidity, these drugs currently represent the mainstay of treatment for prolactinomas. Novel data indicate that these agents can be successfully withdrawn in a subset of patients after normalization of prolactin levels and tumor disappearance, which suggests the possibility that medical therapy may not be required throughout life. Nevertheless, multimodal therapy that involves surgery, radiotherapy or both may be necessary in some cases, such as patients who are resistant to the effects of dopamine agonists or for those with atypical prolactinomas. This Review reports on efficacy and safety of pharmacotherapy in patients with prolactinomas.

Advances in the treatment of prolactinomas

Prolactinomas account for approximately 40% of all pituitary adenomas and are an important cause of hypogonadism and infertility. The ultimate goal of therapy for prolactinomas is restoration or achievement of eugonadism through the normalization of hyperprolactinemia and control of tumor mass. Medical therapy with dopamine agonists is highly effective in the majority of cases and represents the mainstay of therapy. Recent data indicating successful withdrawal of these agents in a subset of patients challenge the previously held concept that medical therapy is a lifelong requirement. Complicated situations, such as those encountered in resistance to dopamine agonists, pregnancy, and giant or malignant prolactinomas, may require multimodal therapy involving surgery, radiotherapy, or both. Progress in elucidating the mechanisms underlying the pathogenesis of prolactinomas may enable future development of novel molecular therapies for treatment-resistant cases. This review provides a critical analysis of the efficacy and safety of the various modes of therapy available for the treatment of patients with prolactinomas with an emphasis on challenging situations, a discussion of the data regarding withdrawal of medical therapy, and a foreshadowing of novel approaches to therapy that may become available in the future.

The effects of perphenazine and bromocriptine on follicular dynamics and endocrine profiles in anestrous pony mares

Nineteen anestrous pony mares were used in a project designed to determine the effects of altered prolactin concentrations on follicular dynamics and endocrine profiles during spring transition. The dopamine antagonist, perphenazine, was administered daily to mares (0.375 mg/kg body weight) in Group A (n = 6), while Group B mares (n = 7) received 0.08 mg/kg metabolic weight (kg75) dopamine agonist, 2-bromo-ergocriptine, intramuscularly twice daily. Mares in Group C (n = 6) received 0.08 mg/kg75, i.m., saline twice daily. Treatment began January 20, 1994, and continued until ovulation occurred. Mares were teased 3 times weakly with an intact stallion. The ovaries of the ponies were palpated and imaged weekly using an ultrasonic B-mode unit with a 5 Mhz intrarectal transducer until they either exhibited estrual behavior and had at least a 20-mm follicle, or had at least a 25-mm follicle with no signs of estrus. At this time, ovaries were palpated and imaged 4 times weekly. Blood samples were obtained immediately prior to ultrasonic imaging for measurement of prolactin, FSH and estradiol-17 beta. Perphenazine treatment advanced the spring transitional period and subsequent ovulation by approximately 30 d. Group A exhibited the onset of estrual behavior earlier (P < 0.01) than control mares. In addition, Group A mares developed large follicles (> 30 mm) earlier (P < 0.01) than Group B mares, with least square means for Groups A and B of 47.0 +/- 8.8 vs 88.1 +/- 8.2 d, respectively. Control mares developed 30-mm follicles intermediate to Groups A and B at 67.3 +/- 8.8 d. Bromocriptine decreased (P < 0.05) plasma prolactin levels throughout the study, while perphenazine had no significant overall effect. However, perphenazine treatment did increase (P < 0.05) mean plasma prolactin concentrations from Day 31 to 60 of treatment. There were no differences in mean plasma FSH or estradiol-17 beta between treatment groups. We concluded that daily perphenazine treatment hastened the growth of follicles and subsequent ovulation while bromocriptine treatment appeared to delay the growth of preovulatory size follicles without affecting the time of ovulation.

Effect of reserpine on the inhibition of prolactin released from different pituitary constructs in vitro by dopamine, bromocriptine and apomorphine

Hourly release of Prolactin by pituitary constructs 1 whole pituitary (PI), adenohypophysis (P-N) and pituitary-hypothalamus co-incubate (PHC) were compared. Adenohypophysis secreted significantly more prolactin than PI and PHC, while PHC secreted significantly less than PI. Co-incubation of (P-N) with posterior pituitary reduced the elevated secretion of prolactin. Addition of dopamine (10(-7) M), bromocriptine (10(-7) M) and apomorphine (5 x 10(-8) M) to these constructs did not affect the release of prolactin from PI but inhibited the same from (P-N) and PHC. Treatment with reserpine increased serum prolactin levels but intrapituitary prolactin contents were decreased. Hourly release of prolactin from pituitary constructs derived from reserpine-treated rats was significantly reduced as compared to ascorbic acid--treated controls. Inclusion of dopamine (10(-7) M), bromocriptine (10(-7) M) and apomorphine (5 x 10(-8) M) in these constructs inhibited prolactin secretion further. In vitro addition of perphenazine stimulated the release of prolactin by PHC but was without any effect on PI and (P-N). The data are interpreted to suggest that dopamine in posterior pituitary may be an important determinant of hypothalamic modulation of prolactin secretion.

Comparative evaluation of lisuride and terguride, ergot alkaloid derivatives, on the field-stimulated vas deferens of mouse

The ergot alkaloid derivatives, lisuride (LIS) and terguride (TDHL), known to interact with central dopamine receptors as agonist and partial agonist, respectively, were studied on the field-stimulated mouse vas deferens, where recently the existence of presynaptic dopamine receptors has been evidenced. LIS was a competitive antagonist at prejunctional alpha 2 and DA1 receptors situated on the sympathetic nerve terminals of the mouse, with a pA2 value of 9.2 and 9.1, respectively. LIS was also able to antagonize the effects of LY 171555, selective DA2 agonist, but the type of interaction cannot be conceptualized in terms of competitive antagonism. Likewise, the type of interaction of TDHL with dopaminergic and adrenergic agonist-activated sites is not suggestive of a competitive antagonism. Based on these results, it seems that central and peripheral pharmacologic profiles of LIS and TDHL cannot be overlapped, LIS being a potent DA1- and alpha 2-antagonist with a high degree of specifity for these receptors.

Immunocytochemical studies on the pituitary gland and spontaneous pituitary tumors of Sprague-Dawley rats

The review of our studies indicates a predictive value of the pituitary gland and spontaneous pituitary tumors of Sprague-Dawley rats for detecting and evaluating the effects and interactions of estrogens and dopamine agonists on the pathogenesis, functional morphology and therapy of human pituitary tumors, such as prolactinomas, gonadotroph adenomas and null cell adenomas. The functional classification of spontaneous pituitary tumors in old female Sprague-Dawley rats reveals a diversity of hormone content and morphologic appearance. They seem to be useful models of the human disease.

Prolactin desensitizes the prostaglandin E1-dependent adenylyl cyclase in the rat prostate gland

Prior exposure of the rat ventral prostate to a high dose of ovine prolactin in vivo or in vitro caused the specific desensitization of the prostaglandin E1-dependent adenylyl cyclase. Maximal desensitization was achieved in vivo 6 h after exposure to 100 micrograms prolactin and complete resensitization occurred after 7 days. No heterologous desensitization of the response of the cyclase to other hormones tested was observed. Incubation of isolated secretory cells with prolactin and prostaglandin E1 desensitized the subsequent response to the same prostaglandin. Simultaneous exposure of the cells to indomethacin prevented the prolactin-induced effect. Prolactin could also induce similar changes in the prostaglandin E1-dependent cyclase of rat Leydig cell tumour cells in vivo, suggesting that this may represent a phenomenon shared by other prolactin target organs. This study supports the hypothesis that prostaglandins may constitute second messengers for prolactin effects on the prostate gland.

Novel 8 alpha-ergolines with inhibitory and stimulatory effects on prolactin secretion in rats

Four derivatives of the ergot dopamine (DA) agonist lisuride (LIS), namely 6-n-propyl-lisuride (6-n-propyl-LIS), transdihydrolisuride (TDHL), 6-n-propyl-transdi-hydrolisuride (6-n-propyl-TDHL) and 2-bromolisuride (2-Br-LIS) were investigated in female rats with regard to their influence on hyperprolactinaemia induced by pretreatment with reserpine (2 mg/kg i.p., 24 h) at various intervals following their subcutaneous or oral administration (0.05 mg/kg). Two hours after administration, LIS, 6-n-propyl-LIS, and 6-n-propyl-TDHL caused a statistically significant inhibition of reserpine-induced hyperprolactinaemia of about the same extent. Eight hours after administration 6-n-propyl-LIS and 6-n-propyl-TDHL were as active as after 2 h in inhibiting prolactin (PRL) secretion whereas LIS was almost ineffective in this respect. TDHL caused a statistically significant inhibition of PRL secretion at 2 and 8 h after oral administration; this effect was less pronounced after s.c. administration. In contrast to the aforementioned derivatives 2-Br-LIS further increased the reserpine-induced hyperprolactinaemia. In normal male rats pretreatment with 2-Br-LIS (0.025-6.25 mg/kg s.c., 2 h) dose-dependently stimulated PRL secretion. The present data support the assumption of the longlasting DA agonistic action of 6-n-propyl-LIS and 6-n-propyl-TDHL and of the antidopaminergic properties of 2-Br-LIS recently derived from behavioural studies.

Pituitary secretion after administration of a new cerebroactive drug, fipexide

The effect of a single oral dose of 400 mg fipexide on pituitary secretion was investigated in 10 elderly non-endocrine patients. Fipexide induced significant decrease (P less than 0.05) in serum prolactin (PRL) values at 90 and 120 min after drug administration, without affecting serum growth hormone (GH), gonadotropin (LH and FSH), thyrotropin (TSH) and cortisol values. Fipexide was unable to modify metoclopramide-induced PRL release in five of these patients. Our results show that this drug acts as a mild dopamine (DA) agonist, probably not directly affecting hypothalamic and/or pituitary DA receptors but indirectly via a reduced DA re-uptake at the pre-synaptic level.

The history and pharmacology of dopamine agonists

The recognition of the dopaminergic properties of some ergot derivatives has initiated new therapeutical approaches in endocrinology as well as in neurology. The pharmacological characterization of the different ergot derivatives during the last decade has largely improved our understanding of central dopaminergic systems. Their development has yielded valuable information on the pharmacology of dopamine receptors involved in the regulatory mechanisms of prolactin secretion and in striatal functions. The clinical application of such new neurobiological concepts has underlined the therapeutical interest of such compounds either in the control of prolactin-dependent endocrine disorders or in the treatment of parkinsonism. Owing to their pharmacological profiles, dopaminergic agonists represent a valuable clinical option especially in the management of Parkinson's disease in view of the problems arising from chronic L-Dopa treatment.

Autoreceptors mediate the inhibition of dopamine synthesis by bromocriptine and lisuride in rats

The administration of bromocriptine and lisuride to rats caused a decrease in striatal dopamine (DA) synthesis, as measured by 3,4-dihydroxy-phenylalanine (DOPA) accumulation after decarboxylase inhibition. DOPA formation was inhibited by a maximum of about 60% of control values by bromocriptine and lisuride, 5.0 and 0.3 mg/kg, respectively. Both compounds showed very similar time-courses for the effect and failed to modify DOPA accumulation during the first 30 min. Pretreatment with (-)-sulpiride (50 mg/kg i.p.), a specific D2-receptor blocker, completely prevented the inhibitory effect of bromocriptine and lisuride on DOPA accumulation. Finally, both compounds significantly reversed the gamma-butyrolactone (GBL) (700 mg/kg i.p.)-induced DOPA accumulation at doses (0.25 and 0.015 mg/kg, respectively) that were inactive in normal rats. The data suggest that bromocriptine and lisuride act as agonists on D2-presynaptic autoreceptors which have different sensitivity to the agonist according to the basal firing rate of DA neurons.

Multiple postsynaptic dopamine receptors and behavioral manifestation

Previously we demonstrated the existence of non- and positive-cooperative dopamine receptors in rat striatum in [3H] apomorphine binding experiments. Non-cooperative sites were sensitive to the inhibition of sulpiride while cooperative sites were not. In the present study results dealing with the involvement of those two types of postsynaptic dopamine receptors in different behavior manifestations is shown employing lisuride hydrogen maleate (LHM). LHM elicited contralateral turnings in 6-hydroxydopamine lesioned rats unilaterally in the striatum whereas it caused ipsilateral turnings in kainic acid lesioned rats as was observed following the administration of apomorphine. Furthermore, the effect of LHM on rotating behavior was abolished by the pretreatment with sulpiride. On the other hand, LHM inhibited apomorphine induced stereotyped behavior whereas the sulpiride failed to block it. These results suggested the dual action of LHM on multiple postsynaptic dopamine receptors. The results also indicated that non-cooperative postsynaptic dopamine receptors are involved in rotating behavior while cooperative receptors participate in the elicitation of stereotypy.

Dopaminergic modulation of adenylate cyclase stimulation by vasoactive intestinal peptide in anterior pituitary

The activation of adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] by vasoactive intestinal peptide (VIP) was used as a model to investigate the molecular mechanisms triggered by the occupancy of dopamine recognition sites in rat anterior pituitary. Dopamine failed to change the basal enzyme activity, but it inhibited the stimulation of adenylate cyclase elicited by VIP. Apomorphine, 2-amino-6,7-dihydroxy-1,2,3,4-tetrahydronaphthalene, and 2-bromo-alpha-ergocryptine mimicked the effect of dopamine, whereas (-)-sulpiride and and classical neuroleptics antagonized it. Dopamine failed to modulate the activation of pituitary adenylate cyclase by prostaglandin E1, which does not increase prolactin secretion. From these results we infer that stimulation of D-2 (dopamine) receptors may affect pituitary secretion by inhibiting the activation of anterior pituitary adenylate cyclase by VIP or other secretagogues.

Characterization of ergot and non-ergot serotonin antagonists by prolactin and growth hormone profiles during wakefulness and sleep

In order to further clarify the involvement of serotonin in the control of secretion of pituitary lactogens, diurnal and sleep prolactin (PRL) and growth hormone (GH) profiles were investigated in healthy subjects treated with ergot and non-ergot serotonin antagonists. A group of 10 subjects received a single oral dose of 2 mg each of pizotifen, methysergide, and the dopaminergic drug bromocriptine as reference substance, in comparison with placebo. Blood was collected at hourly intervals for 6 h. Another group of 10 individuals received either a placebo, 2.5 mg bromocriptine (n = 6) twice daily for 4 days or pizotifen (n = 10) 0.5 mg 3 times daily for 12 days before undergoing EEG recording and blood sampling during night sleep. The diurnal plasma profiles of PRL and GH were not modified by pizotifen, a non-ergot drug. Methysergide and bromocriptine, two ergot derivatives, significantly (P < 0.01 and P < 0.001 respectively) suppressed the basal secretion of PRL throughout the trial and increased plasma GH significantly (P < 0.01). The sleep profile of PRL was not modified by pizotifen but there was a moderate reduction in GH reaching the level of significance (P < 0.02) between hours 1 and 2 of sleep. Bromocriptine suppressed completely PRL secretion throughout the entire sleep period and significantly (P < 0.05) prolonged the secretory profile of GH. The results indicate the presence in the ergot molecule of a dopaminergic moiety responsible for PRL inhibition and GH stimulation. This effect is independent of the serotonin active component of the drug.

Stimulatory action of lisuride on dopamine-sensitive adenylate cyclase in the rat striatal homogenate

Effect of lisuride, an ergot derivative of isolysergic structure, on dopamine-sensitive adenylate cyclase was studied in the homogenate of rat corpus striatum. Stimulatory action of lisuride, similar to the actions of dopamine and apomorphine, on striatal adenylate cyclase was potentiated significantly by guanosine triphosphate (GTP) and by guanyl-5'-yl imidodiphosphate (GMP-PNP), although with lisuride alone, there was only a slight stimulation. The maximal stimulation attained in the presence of GTP corresponded to about 1.4 times the basal rate of cyclic AMP formation in the homogenate and was abolished by an addition of haloperidol. Lisuride at a concentration about 3 microM inhibited stimulation of cyclic AMP formation by dopamine. The effect of lisuride and the extent of potentiation by the guanyl nucleotides were almost comparable to the effects of apomorphine, under corresponding conditions. Thus, lisuride, like apomorphine, acts as a partial agonist-antagonist, and has the ability to stimulate the dopamine-sensitive adenylate cyclase in the rat corpus striatum.

Size reduction of a prolactin secreting adenoma during long-term treatment with the dopamine agonist lisuride

A 38-year-old amenorrhoeic woman suffering from a prolactin (PRL) secreting adenoma, which had suprasellar extension as shown by caroe agonist (lisuride). PRL levels were lowered and after 1 year of treatment CAT showed a marked reduction of the tumour size. After 2 years of treatment menstruation returned and CAT demonstrated a further reduction of the adenomatous tissue. This study supports the suggestion that dopamine agonists possess an anti-proliferative effect on tumoural lactotrophic cells of humans.

Effects of lisuride on body temperature of rats and rabbits: relation to microsomal biotransformation and dopaminergic receptor stimulation

In rats, lisuride, either administered systemically or intracerebroventricularly induced a dose-related hypothermia. This effect was selectively antagonized by blockade of DA receptors in the CNS but not by inhibition of catecholamine synthesis or blockade of serotoninergic receptors. Also a blocker of "peripheral" DA receptors failed to antagonize the hypothermic effect of lisuride in rats. Induction of rat liver microsomal drug-metabolizing enzymes by phenobarbital counteracted lisuride-induced hypothermia. In rabbits lisuride induced a hyperthermic response which was sensitive to both pimozide and metergoline pretreatment. These findings indicate that stimulation of brain DA receptors involved in thermoregulation is responsible for the changes in body temperature indiced by lisuride in rats and rabbits and that these effects are caused by the drug itself and do not require previous biotransformation into an active metabolite.

Effect of lisuride on inhibition of lactation and serum prolactin

Lisuride, a new semisynthetic ergot derivative, was given to 53 women to inhibit lactation; 26 women had 300 micrograms daily and 27 had 600 micrograms daily for seven days. Eight lactating women acted as controls. Lisuride effectively inhibited lactation and also suppressed the serum prolactin levels; the latter effect was dose related. Lisuride produced no untoward side effects.

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.

Hypothermic action of lisuride in rats and differences to bromocriptine in the antagonistic effect of neuroleptics

The semisynthetic ergot derivative lisuride induced dose- and time-dependent hypothermia in rats placed in a cold environment (+4 degrees C). As regards dosage, lisuride was more than 100 times more effective in this test model than bromocriptine. The effect of both drugs could be reduced by pretreatment with the dopamine antagonist haloperidol, which indicated a dopaminergic action of both drugs. In contrast, the hypothermic effect of lisuride could not be impaired by pretreatment with sulpiride, whilst the effects of bromocriptine were clearly antagonized by this drug. This results could be explained by a different affinity of these drugs to the same receptors, or, more likely, by a different mechanism of action by which lisuride and bromocriptine activate dopaminergic systems.

Neuroendocrine effects of neuropsychotropic drugs and their possible influence on toxic reactions in animals and man -- the role of the dopamine-prolactin system

As an example for the importance of the neuroendocrine system in the toxicological evaluation of neuropsychotropic drugs, the influence of functional dopaminergic agonists and antagonists on the secretion of prolactin is studied. In rats, all functional dopamine antagonists (reserpine alone or combined with alpha-methyl-p-tyrosine or benserazide, haloperidol, spiroperidol, sulpiride) increased serum PRL levels. Dopaminergic agonists (apomorphine, piribedil, d-amphetamine, L-DOPA, and the ergot derivatives bromocriptine and lisuride) all caused a decrease of serum prolactin levels. The same effect could be observed also after treatment with other ergot derivatives such as d-LSD, methergoline, methysergide and ergotamine. Also in this case, the prolactin-lowering effect seems to be related to dopaminergic activity. This was suggested by the inhibitory effect of pretreatment with the dopamine antagonist spiroperidol or with sulpiride on the prolactin-lowering effect of lisuride. In dogs, thyrotropin releasing hormone (TRH) increased and lisuride decreased serum prolactin levels determined with a new radioimmunoassay. As an example for the situation in humans, the effects of the dopamine antagonist sulpiride and of the dopamine agonist bromocriptine were described. The prolactin levels were higher in the presence of estrogens. The relevance of these neuroendocrine effects of neuropsychotropic drugs on physiological systmes in animals and man is discussed.