Effect of lithium on hypothalamic-pituitary dopaminergic function

Stereospecificity of the dopamine receptor mediating the growth hormone response to apomorphine in man. Short communication

The stereospecificity of the D-2 receptor mediating the growth hormone (GH) response to apomorphine (Apo) and the D-2 receptor regulating prolactin (PRL) secretion were investigated in 10 normal men by examining the effects of cis-flupenthixol (cis-Fx) and trans-flupenthixol (trans-Fx). cis-Fx (1 mg six hourly times four doses) antagonized the GH response to Apo HCl (0.5 mg sc) and increased basal serum PRL concentrations whereas the trans-isomer showed no effect. These findings (a) provide further evidence that the GH response to Apo is mediated by stimulating dopamine (DA) receptors, and, (b) demonstrate stereospecificity of the DA receptor mediating the GH response to Apo and the DA receptor regulating PRL secretion.

The effects of drugs on tests of thyroid function

Many drugs affect tests of thyroid function through alterations in the synthesis, transport and metabolism of thyroid hormones, as well as via influences on thyrotrophin (TSH) synthesis and secretion. Despite effects on circulating thyroid hormone and TSH levels, few drugs result in important changes in clinical thyroid state, but difficulty in interpretation of thyroid function tests often results. Commonly prescribed drugs including anti-convulsants, non-steroidal anti-inflammatory drugs, beta-adrenoceptor antagonists, steroid hormones and heparin may result in abnormal thyroid function tests in the absence of clinical features of thyroid dysfunction. In contrast, lithium and iodine containing drugs, including radiographic contrast agents and amiodarone, may result rarely in overt thyroid disease.

Lithium increases 5-HT-mediated neuroendocrine responses in tricyclic resistant depression

The addition of lithium to the tricyclic antidepressant medication of 11 depressed patients resulted in an increase in the prolactin response to L-tryptophan after both 4 days and 4 weeks of lithium treatment. There was also a significant fall in Hamilton Depression scores. The results suggest that lithium and tricyclic antidepressants may act synergistically to enhance certain aspects of brain 5-HT function in depressed patients.

Lithium increases 5-HT-mediated prolactin release

The effects of short-term (3-4 days) lithium treatment on the prolactin responses to intravenous clomipramine (0.1 mg/kg), metoclopramide (5 micrograms/kg) and haloperidol (2.5-5 micrograms/kg) were assessed in male volunteers. Prolactin responses to clomipramine were significantly enhanced by lithium while those following administration of haloperidol and metoclopramide were not significantly altered. Lithium did not change the cortisol response to clomipramine. The results suggest that lithium may selectively enhance 5-HT mediated prolactin release. These data are consistent with the hypothesis that synergistic effects of lithium and clomipramine on brain 5-HT function may be involved in their therapeutic effect in resistant depression.

Childhood and adolescent depression. II: Research in clinical populations

The tremendous increase in interest in childhood and adolescent depression that has occurred since the early 1970s has resulted in a large and contradictory literature. Development of the concept of childhood depression, and the many clinical studies of depression and its concomitants, both psychosocial and biological, are critically reviewed. A number of methodological and theoretical problems are discussed.

Apomorphine in the evaluation of dopaminergic function in man

1. Apomorphine (Apo), a short acting dopamine (DA) receptor agonist, stimulates growth hormone (GH) secretion, decreases prolactin secretion, induces yawning, penile erections and other physiological effects in man. An effect on behavior, movement disorders and alcoholism has also been described. 2. Apo-mediated responses are used to evaluate DA function in psychiatric and neurological disorders. Many of the studies in schizophrenia using the GH response to Apo as an index of central DA function are difficult to interpret because of failure to control for key variables. 3. The GH response to Apo is a useful system to evaluate the effects of various drugs including peptides which may not cross the blood brain barrier on DA function in man. 4. Apo is a potent sedative. Specific antimanic, antischizophrenic, and anticraving effects in alcoholics have not been convincingly demonstrated. Side effects of Apo and failure to use active placebo make double-blind studies difficult. 5. Apo improves parkinsonian symptoms and certain forms of reflex epilepsy but beneficial effects in other involuntary movement disorders requires further documentation. 6. Apo may be a useful agent to evaluate DA function in impotent patients and predict a therapeutic response to long-acting dopaminergic agents. 7. Impairment of DA function may play a role in diabetic impotence. 8. The development of a simple polygraphic method to monitor the yawning response to Apo may facilitate clinical studies on the basic physiology of yawning in man and the use of the yawning response as a measure of central DA function in schizophrenia and other clinical disorders. 9. The use of Apo with 18F-fluorodeoxyglucose positron emission tomography to examine regional DA function in man opens up a promising area of research. 10. Though long-acting orally active aporphine DA agonists and antagonists have been developed the problem of tolerance may limit their therapeutic potential.

Effect of sulpiride, an atypical neuroleptic, on apomorphine-induced growth hormone secretion

Sulpiride (100 mg IM), an atypical neuroleptic, which does not block dopamine (DA) receptors that are linked to adenylate cyclase, abolished the growth hormone (GH) response to the DA receptor agonist, apomorphine (Apo) HCl (0.5 mg SC) in seven healthy male subjects. These results suggest that Apo increases GH secretion in man by an effect on DA receptors that are not linked to adenylate cyclase.

Hypothalamic-pituitary dopaminergic function in hepatic failure in man

The growth hormone (GH) response to apomorphine HCl (Apo) (0.75 mg sc), a dopamine (DA) receptor agonist, was assessed in healthy chronic alcoholics without cirrhosis (N = 20) and in patients with alcoholic cirrhosis both with (N = 5) and without (N = 14) hepatic encephalopathy (HE). A significant number of cirrhotic patients with (P less than 0.004) and without (P less than 0.002) HE had an impaired GH response (peak increment less than 5 ng/ml) compared with non-cirrhotic individuals. An impaired GH response was independent of the presence of HE. The magnitude of the GH response was unrelated to plasma oestrone, oestradiol, or progesterone concentrations but was significantly correlated with plasma testosterone levels (P less than 0.01). None of the patients with an abnormally low testosterone concentration showed a normal GH response. None of the subjects with HE showed an arousal response to Apo. These results suggest that DA receptor sensitivity is decreased in liver cirrhosis and that this decrease is related to inadequate circulating levels of testosterone. The occurrence of HE is independent of impaired DA function. The present study only evaluates DA function in the hypothalamic-pituitary axis and therefore may not reflect changes in other regions of brain.

Effect of domperidone on apomorphine-induced growth hormone secretion in normal men

Domperidone, a peripheral dopamine (DA) receptor blocker which poorly crosses the blood-brain barrier and which is inactive towards dopamine-sensitive adenylate cyclase, in a dose (100 micrograms/kg) sufficient to increase serum prolactin levels at least 5-fold, decreased the growth hormone (GH) response to the DA receptor agonist, apomorphine HCI (Apo) (0.5 gm s.c.) in each of six normal men examined. The mean GH increment at 30, 45, 60 and 75 min following Apo injection, the mean individual peak increment and the mean individual GH secretion (ng min) was significantly decreased by domperidone pretreatment (p less than 0.005 -p less than 0.002). These results indicate that in man Apo stimulates GH secretion by an effect on DA receptors which are not linked to adenylate cyclase and which are situated at a locus in the hypothalamic-pituitary axis that lies outside the blood-brain barrier.

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.

Lithium therapy and thyroid function: a long-term study

Seventy-three patients who had been continuously receiving lithium carbonate for 6 months or more had their thyroid function evaluated clinically and biochemically. Goitre was found in 37%, exophthalmos in 23%, positive thyroid auto-antibodies in 24% and abnormal TRH tests in 49%. It would appear that thyroid failure due to lithium is usually dependent on antibody mediated damage. It is unlikely that lithium has a direct effect on the hypothalamic-pituitary axis.

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

The plasma thyrotropin (TSH) and prolactin (PRL) responses to thyrotropin releasing hormone (TRH) were studied before and during lithium treatment for 3-4 weeks in 6 patients with manic states and 8 control subjects. The plasma TSH responses to TRH were not different between the two groups before lithium treatment. Lithium administration did not alter non-stimulated secretion of TSH in any groups, but resulted in exaggerated responses of plasma TSH to TRH in both groups. No difference between two groups was observed in plasma TSH responses to TRH. The basal plasma PRL concentration did not differ between the two groups and was not affected by lithium administration to either group. The plasma PRL responses to TRH in female subjects were greater than those in male subjects. In females, the plasma PRL responses to TRH in manic patients were significantly higher than those in control subjects before the treatment. Lithium administration caused enhanced responses to TRH in patients when compared to pretreatment levels, but not in control subjects. Although the small number of male subjects limits conclusions, pretreatment plasma PRL responses to TRH in male manic patients were apparently greater than those in control subjects. However, lithium administration appeared not to affect the responses of plasma PRL to TRH in manic patients when compared to pretreatment levels. The augmented responses of plasma PRL to TRH in patients with manic states suggest the existence of some abnormality in the hypothalamo-pituitary axis. Thus, the effect of the anti-manic agent on PRL secretion in manic patients may suggest the mechanism by which the drug affects manic symptoms.