Effect of lithium on prolactin responses to thyrotropin releasing hormone in patients with manic state

Molecular targets of lithium action

Lithium is an effective drug for both the treatment and prophylaxis of bipolar disorder. However, the precise mechanism of lithium action is not yet well understood. Extensive research aiming to elucidate the molecular mechanisms underlying the therapeutic effects of lithium has revealed several possible targets. The behavioral and physiological manifestations of the illness are complex and are mediated by a network of interconnected neurotransmitter pathways. Thus, lithium's ability to modulate the release of serotonin at presynaptic sites and modulate receptor-mediated supersensitivity in the brain remains a relevant line of investigation. However, it is at the molecular level that some of the most exciting advances in the understanding of the long-term therapeutic action of lithium will continue in the coming years. The lithium cation possesses the selective ability, at clinically relevant concentrations, to alter the PI second-messenger system, potentially altering the activity and dynamic regulation of receptors that are coupled to this intracellular response. Subtypes of muscarinic receptors in the limbic system may represent particularly sensitive targets in this regard. Likewise, preclinical data have shown that lithium regulates arachidonic acid and the protein kinase C signaling cascades. It also indirectly regulates a number of factors involved in cell survival pathways, including cAMP response element binding protein, brain-derived neurotrophic factor, bcl-2 and mitogen-activated protein kinases, and may thus bring about delayed long-term beneficial effects via under-appreciated neurotrophic effects. Identification of the molecular targets for lithium in the brain could lead to the elucidation of the pathophysiology of bipolar disorder and the discovery of a new generation of mood stabilizers, which in turn may lead to improvements in the long-term outcome of this devastating illness (1).

Endocrine effects of lithium carbonate in healthy premenopausal women: relationship with body weight regulation

The mechanisms involved in Li-induced weight gain remain unclear. The higher frequency of obesity in women than in men under Li treatment, suggests a role for reproductive hormones. The serum levels of the following hormones were evaluated in healthy young women at diverse stages of a control menstrual cycle, and during Li carbonate (900 mg/day) or placebo administration: prolactin, luteinizing hormone, follicle-stimulating hormone, 17-1 estradiol, progesterone, thyroxine, thyrotropin, cortisol, dehidroepiandrosterone sulfate, free testosterone, leptin and an oral glucose tolerance test, in order to measure the areas under the glucose and insulin curve. The body weight was assessed the day before and the last day of treatment. The Li serum levels 15 hours after the last dose were 0.31 +/- 0.1 mEq/L. No significant changes in body weight and in the normal fluctuations of the reproductive hormones along the menstrual cycle were observed during Li administration. An increase in the serum levels of thyrotropic hormone ( p = 0.0001) was the only significant effect of Li, which may predispose to excessive weight gain after prolonged administration of the cation. The remarkable lack of effects of Li on these hormones, question the pertinence of studies conducted in healthy volunteers for the comprehension of the obesity observed in psychiatric patients who may be particularly prone to gain weight under prolonged treatment with high dose of Li.

Effects of i.c.v. lithium chloride administration on monoamine concentration in rat mediobasal hypothalamus

We investigated the acute effects of a single i.c.v. injection of lithium chloride (LiCl) the neuroamine content of the rat mediobasal hypothalamus (MBH). The effects of lithium on amine synthesis and degradation enzymes were also studied in vitro. Noradrenaline (NA), dopamine (DA), serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) concentrations were reduced 10 min after i.c.v. injection of 24 nmol of LiCl and returned to control values 30 min after the injection. Two nmol of LiCl reduced the concentration of DA (10 and 30 min after injection) and 5-HIAA (30 min after injection). LiCl (0.5-10 mM) inhibited tyrosine hydroxylase activity (catecholamine synthesis) in vitro in a concentration dependent manner. The i.c.v. administration of a high dose of LiCl reduced the content of neuroamines in the MBH. This might result from and inhibition of synthesis. A possible link between the observed changes and some reported side effects of lithium therapy is discussed.

Inositol monophosphate esterase inhibition by lithium in normal human studies using neuroendocrine tests. Part I. PRL and TSH responses to TRH

1. Many neuroendocrine events are mediated by intracellularly second messengers, among which are the breakdown of phosphatidylinositol 4,5-biphosphate (PIP2). 2. Lithium (Li) was shown in therapeutic doses to be a specific inhibitor of the enzyme inositol monophosphate esterase Li reduces the turnover of PIP2 and diminishes the cell responses. 3. In order to investigate this new mode of action of Li the authors studied the influence of acute dose of Li on the response of prolactin (PRL) and thyrotropin (TSH) to thyrotropin stimulating hormone (TRH), a stimulation mainly mediated through the activation of the turnover of PIP2. 4. In seven normal subjects a single dose of 19.80 meq of Li reduced the response of PRL in 4, and augmented it in 3 subjects: Li decreased the TSH response in 4 subjects, it was increased in 1 and remained unchanged in 2. 5. These results are discussed in the light of the different interactions between hormone secretion, and the fact that adenopituitary is located out of the brain blood barrier.

Acute antidepressant effect of lithium is associated with fluctuation of calcium and magnesium in plasma. A double-blind study on the antidepressant effect of lithium and clomipramine

In a double-blind study on 22 patients with major depressive disorder the effects of lithium and clomipramine on signs and symptoms and on calcium and magnesium in plasma were compared. Ratings of antidepressant and side effects were performed by 2 psychiatrists at the end of a placebo period of 5-7 days and after treatment for 2 and 4 weeks. Psychopathology was rated by 15 reported and 4 observed items from the Comprehensive Psychopathological Rating Scale (CPRS). Eleven items present in 72-100% of the patients were used to evaluate the effect of the two drugs. After 2 weeks of treatment the rated scores dropped for more than half of the CPRS items. After 4 weeks the scores for all but one item were reduced in both groups. The sums of scores were significantly reduced after 2 weeks in both groups and after 4 weeks global scores were reduced as well. The drugs had notable and similar antidepressant effects. Lithium treatment was associated with fluctuations in calcium and magnesium levels in plasma not seen during clomipramine treatment. Serum prolactin increased during clomipramine treatment but was unaffected by lithium treatment. No correlations were found between the sum of rating scores and blood levels of drugs, prolactin, calcium or magnesium.

Luteinizing hormone responses to luteinizing hormone releasing hormone (LHRH) in acute mania and the effects of lithium on LHRH and thyrotrophin releasing hormone tests in volunteers

The endocrine responses to Luteinizing Hormone Releasing Hormone (LHRH) of eight drug-free males with mania were determined. Basal levels of Luteinizing Hormone (LH) and the plasma levels following injection of LHRH were elevated in patients compared with controls; Follicle Stimulating Hormone (FSH) and testosterone were not different. Elevated levels of LH have been described previously in recovered manic patients and have been suggested to be state-independent features of mania. In order to clarify the status of this finding, the effects of lithium administration upon hormone responses to LHRH in six male volunteers were also investigated, together with the effects upon Thyrotrophin Releasing Hormone (TRH) stimulation of Thyroid Stimulating Hormone (TSH) and prolactin release. Lithium increased the basal levels of LH and levels after injection of LHRH without effect upon FSH and testosterone. Lithium also increased basal and TRH stimulated release of TSH and basal prolactin levels. Lithium was without effect upon prolactin responses to TRH. The results are discussed in relation to current information on the mechanism of lithium's action. The implications for neuroendocrine work on recovered patients taking lithium are also explored.

Drug-induced changes in prolactin secretion. Clinical implications

Prolactin secretion is affected by various diseases as well as by many drugs in humans and animals. While marked hyperprolactinaemia suggests the presence of a pituitary tumor, moderate changes may also occur in various endocrine or non-endocrine disorders. Drugs can interfere with prolactin regulation via complex mechanisms at the hypothalamus or at the pituitary site, but possible changes in prolactin metabolism are poorly understood as yet. This survey of the literature up to June 1986 covers the influence of various groups of drugs and agents on the plasma prolactin level under various conditions. It contains information that will facilitate evaluation of whether hyper- or hypoprolactinaemia may result from therapeutic intervention or must be related to an underlying disease. It is obvious that more subtle changes can be revealed by the use of dynamic tests either to stimulate or to suppress prolactin secretion.

TSH response to TRH and haloperidol response latency in psychoses

Thyroid-stimulating hormone (TSH) response to thyrotropin-releasing hormone (TRH) was measured in 19 acutely psychotic (DSM-III schizophrenia, 7; schizophreniform, 2; schizoaffective, 3; affective, mood-incongruent psychosis, 5; manic, mood-congruent psychosis, 2) drug-free patients prior to systematic trials of lithium and/or haloperidol. TSH response was not associated with sex, age, baseline T4, or baseline TSH. A reduced TSH response was associated with affective diagnosis and was a significant predictor of a positive, rapid response to neuroleptic treatment.

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.

Sleep during mania in manic-depressive males

Sleep polygraphic recordings were performed in six unmedicated male manics, in age and sex matched unipolar and bipolar depressives and in normal controls. No difference was evidenced between manics, depressives and controls when percentages of sleep stages 1, 2, 3, 4 and REM were considered. Manics demonstrated poorer sleep efficiency, longer sleep onset latency and reduced sleep period time than normal controls but no more so than in our depressed patients. None of the classical sleep disturbances reported in depression (short REM latency, decreased delta sleep and increased REM density) were observed in mania suggesting that with the exception of sleep continuity disturbances, sleep in mania is comparable to sleep in normal subjects.

The effects of lithium on neuroendocrine function in affectively ill patients

Lithium is the primary treatment for manic-depressive illness. The mechanism of action of lithium and its endocrine effects remain unclear. Therefore, the hormone responses to sequential stimuli, namely arginine, TRH, and LHRH, were studied in eight patients with major depression before and during treatment with lithium. The drug was found to elevate baseline TSH and prolactin and to augment both their responses to TRH. No clinically significant effect on sex hormones was noted. The advantages of the experimental design and the implications of the findings for lithium's mechanism of action are discussed.

The neuroendocrinology of mania

The paper reviews the endocrine findings in manic patients and the effects of treatment, as well as the association between endocrine conditions or hormonal treatments and abnormal states of elation resembling mania. The findings are discussed in relation to hypotheses about the neurochemical basis of mania, particularly the mesolimbic dopamine hypothesis.

Lithium-induced changes in the plasma and pituitary levels of luteinizing hormone, follicle stimulating hormone and prolactin in rats

Adult male Sprague-Dawley rats, maintained under a controlled photoperiod of LD 14:10 (white lights on at 06:00 h, CST), were injected with lithium chloride and changes in the levels of plasma and pituitary homogenates of luteinizing hormone (LH), follicle-stimulating hormone (FSH) and prolactin (PRL) were examined to evaluate the effects of this anti-manic drug on reproductive function. Two groups of rats were injected with lithium chloride intraperitoneally, twice daily at 09:00 and 16:00 h, for 2 and 7 days at a dosage of 2.5 meq/Kg body weight. Plasma and pituitary levels of LH, FSH and PRL were measured by radioimmunoassay. Plasma levels of LH were significantly (P less than 0.05) increased after 2 days of lithium treatment. In contrast, a significant (P less than 0.005) reduction in plasma levels of LH was evident when lithium injections were continued for 7 days. The plasma levels of FSH remained unaffected by lithium treatment by either time period. Lithium administered for 2 days did not bring about any significant alteration in the plasma levels of PRL, although there was a significant (P less than 0.002) reduction in plasma PRL levels after 7 days treatment. The concentrations of pituitary LH, FSH and PRL remained unchanged after 2 and 7 days of lithium treatment.

Inhibitory effect of lithium on neuroleptic and serotonin receptors in rat brain

We investigated the effect of acute and chronic administration of lithium on neuroleptic receptors ([3H]spiroperidol binding sites) and serotonin receptors ([3H]serotonin binding sites) in rat brain. In the limbic-forebrain, both acute and chronic lithium treatment significantly reduced the density (Bmax) of neuroleptic receptors, without affecting the affinity (Kd) of those receptors. However, lithium treatment had no apparent effect on neuroleptic receptors in the caudate-putamen and frontal cortex in either acute or chronic administrations. On the other hand, acute lithium administration markedly decreased the Kd and Bmax of serotonin receptors in the hippocampus, but not in the cerebral cortex; this distinct observation was also found in animals chronically treated with lithium. These results indicate that lithium has an inhibitory effect on neuroleptic receptors in the limbic-forebrain and on serotonin receptors in the hippocampus. Therefore, it is possible to postulate that these effects of lithium in specific brain regions may be related to the therapeutic mechanism of this drug in affective disorders.

A case of manic state in which lactation occurred after Li2CO3 administration

Li2CO3 alone was administered to a 21-year-old female, who was in a manic state. As a consequence, lactation occurred on about the 50th day after Li2CO3 administration started, and the volume of lactation changed in parallel with the serum Li2CO3 level. The basal plasma PRL concentration and the responses to TRH (500 micrograms) were elevated during Li2CO3 administration. However, both of them returned to within the normal range after the suspension of Li2CO3 administration. From the above-mentioned findings, it is suggested that lactation is closely related to the Li2CO3 administration.

Antagonizing effect of lithium on the development of dopamine supersensitivity in the tuberoinfundibular system

We investigated whether receptor supersensitivity occurs in the tuberoinfundibular dopaminergic system, as reported in the nigrostriatal and mesolimbic areas. Animals received either haloperidol or saline for 2 weeks. Five days after the last injection of haloperidol, animals pretreated with haloperidol showed a significantly longer lasting inhibition of prolactin (PRL) secretion by apomorphine, compared with the controls. This dopamine receptor supersensitivity was also observed on the 12th, but not the 33rd day after the cessation of haloperidol administration. The effect of lithium on this dopamine supersensitivity in PRL release was investigated. All rats were treated with haloperidol and fed either a diet containing lithium carbonate or a diet without lithium for 2 weeks. Lithium administration with haloperidol resulted in the inhibition of PRL-lowering action of apomorphine at 5 days of withdrawal from haloperidol, indicating that the supersensitivity of dopamine receptors of dopamine receptors on pituitary lactotrophs were decreased by lithium. This action of lithium may be related to the prophylactic effect of the drug on the manic-depressive disease.

Lithium in combination with haloperidol or thyrotropin-releasing hormone induces jumping in mice

Lithium (250 mg/kg IP) administered in combination with haloperidol (2-5 mg/kg IP) or thyrotropin-releasing hormone (TRH) (10 or 20 mg/kg, IP) evoked jumping in mice. Jumping elicited by lithium (250 mg/kg) plus haloperidol (4 mg/kg) or TRH (20 mg/kg) was decreased by physostigmine (0.2 mg/kg IP) and phentolamine (10 mg/kg IP), but was increased by atropine (5 mg/kg IP) and clonidine (0.5 mg/kg IP). While the jumping was not affected by either methylatropine (5 mg/kg IP) or propranolol (10 mg/kg IP). Jumping was also induced by haloperidol (4 mg/kg IP), but not by lithium (250 mg/kg IP), administered after atropine (5 mg/kg IP) or clonidine (0.5 mg/kg IP). The results indicate that lithium plus haloperidol or TRH produces jumping in which dopaminergic and cholinergic inhibition as well as noradrenergic activation may be involved.

Inhibition by lithium of dopamine receptors in rat prolactin release

We investigated the effect of lithium on prolactin (PRL) secretion in both urethane-anesthetized rats and right atrial catheter-bearing conscious rats. Basal plasma PRL levels were not significantly altered for 4 h after lithium administration. However, lithium treatment apparently potentiated PRL release by haloperidol in both conscious and urethane-anesthetized rats. In addition, the inhibition by apomorphine of PRL secretion was significantly antagonized by lithium in conscious rats. Lithium had no effect on the enhancement of PRL secretion by either 5-hydroxytryptophan or beta-endorphin in conscious rats. These observations indicate that lithium affects PRL secretion when dopaminergic neural activity is altered. Therefore, it is possible to postulate that the decrease of dopamine receptor sensitivity by lithium may be related to the therapeutic action of the drug on affective disorders.