Effects of alpha-methyl-para-tyrosine (AMPT) in drug-free depressed patients

A variety of biologic studies have demonstrated abnormal regulation of the norepinephrine (NE) system in patients with major depression, suggesting a role for NE in the etiology of depression. Brain NE and dopamine levels can be rapidly reduced by blocking synthesis with the tyrosine hydroxylase inhibitor alpha-methyl-para-tyrosine (AMPT). In the current investigation, AMPT was administered to drug-free depressed patients to evaluate the effect on mood of diminished catecholamine levels. Seventeen drug-free patients meeting DSM-III-R criteria for major depressive episode were tested with AMPT and an active placebo control, diphenhydramine. Testing was accomplished in a double-blind, crossover fashion, with random assignment to test conditions. Each test included baseline evaluation, 2 days with administration of either AMPT or diphenhydramine, and a follow-up day. Diphenhydramine was used as an active control because of the significant sedation associated with AMPT. Behavioral ratings, including visual analogue scales for a variety of feeling states, the Hamilton Depression Rating Scale (HDRS), and plasma for 3-methoxy-4-hydroxyphenelethyleneglycol (MPHG) and homovanillic acid (HVA) levels, were obtained. AMPT significantly reduced plasma HVA by 70% and MHPG by 50%, but it had no significant effects on the HDRS. AMPT also significantly increased visual analogue ratings of "tired" and decreased ratings of "energetic." Diphenhydramine significantly decreased HDRS scores, but the change was small and was not clinically apparent. The lack of AMPT effects on depressed mood, in conjunction with a prior report that large reductions in plasma tryptophan do not systematically alter depressed mood, indicate that monoamine deficiency by itself is insufficient explanation of the cause of depression. The role of the noradrenergic system needs to be considered in relationship to the many other neurobiologic factors that could be involved in the pathophysiology of depression.

Pharmacologic treatment of autonomic dysreflexia in the rat

Autonomic dysreflexic hypertension occurs in up to 80% of spinal cord injury patients with lesions thoracic level 6 or higher. Pharmacologic agents directed at each part of the autonomic dysreflexic circuit were tested for efficacy in a rat model. Guanethidine (15 mg/kg intraperitoneally), alpha-methyl-paratyrosine (20 mg/kg intraperitonally), propranolol (3 mg/kg intraperitonally) and control were each tested on groups of three rats with intrinsic control blood pressure measurements. Results show an increase of 15 +/- 5 mm Hg diastolic pressure in control animals compared with no detectable increase with guanethidine or alpha-methyl-paratyrosine. There was an 11 +/- 2 mm Hg increase in diastolic pressure with propranolol. In conclusion, screening drug trials show that the ganglionic blocking agent, guanethidine, and competitive tyrosine uptake precursor, alpha-methyl-paratyrosine, effectively blocked dysreflexic hypertension, whereas the beta-blocker, propranolol, did not.

Persistent psychosis after reduction in pre- and post-synaptic dopaminergic function

The purpose of this study was to evaluate the hypothesis that neuroleptic non-response in the face of "adequate" DA post-synaptic receptor blockade reflects failure of regulatory mechanisms to decrease DA pre-synaptic activity. Eight chronic schizophrenics, meeting rigorous criteria for neuroleptic non-response, were treated for four weeks with alpha-methylparatyrosine as an adjunct to their previously stable neuroleptic dose. Treatment with AMPT produced a prompt decrease in plasma HVA that was, on average, 72% lower at the end of the study. While there was also strong clinical evidence of reduction in central dopaminergic activity (both a significant reduction in dyskinetic movements and increase in extrapyramidal symptoms), there was virtually no change in severity of psychotic symptoms. Thus, in this group of non-responders, psychotic symptoms persisted despite both extensive dopamine post-synaptic receptor blockade and marked reduction of presynaptic activity. These symptoms may not be directly DA dependent.

An atrial pheochromocytoma-induced hypertensive crisis resistant to nitroprusside

A malignant pheochromocytoma with several unique features was studied. Initially, its histological and catecholamine secretory properties and physiological effects were terminated by an infarct prior to its excision in 1973. However, in 1985 a metastasis was resected from the right atrium. Hypertensive crisis during surgery was controlled by the administration of phentolamine but not by nitroprusside. Within 2 months, it was again detected at this same site. Biochemical studies confirmed its recurrence. The tumor did not respond to chemotherapy with vincristine, cyclophosphamide and dacarbazine, but there has been physiological and biochemical improvement from inhibiting catecholamine biosynthesis with metyrosine. We recommend that both phentolamine and sodium nitroprusside be readily available during resection of a pheochromocytoma.

[Therapy of a malignant sympathetic paraganglioma of the organ of Zuckerkandl--a case report]

We present a case report on a 35-year-old patient in whom a malignant sympathetic paraganglioma of the organ of Zuckerkandl was the cause of severe hypertension with excessive perspiration at night. Since curative surgery was not possible medical treatment was initiated. Interferon alfa 2b (Intron A, Essex Pharma) and the somatostatin-analogue SMS 201-995 (Sandostatin, Sandoz) had no effect on catecholamine production and progression of the tumor. Treatment with alpha-methyl-para-tyrosin (MPT, [Metyrosin], Demser, MSD) turned out to be an effective and well tolerable therapy in this patient with peritoneal carcinosis. Clinical and hormonal progression of the paraganglioma resumed only after two years of therapy, which constitutes the longest documented period of time of successful MPT treatment. The superior efficacy of MPT in our patient should encourage postoperative medical treatment with MPT in malignant pheochromocytoma or malignant paraganglioma, particularly when the tumor turns out to be resistent to alpha blocking drugs.

Dopamine beta-hydroxylase deficiency. A genetic disorder of cardiovascular regulation

Dopamine beta-hydroxylase (DBH) deficiency is a genetic disorder in which affected patients cannot synthesize norepinephrine, epinephrine, and octopamine in either the central nervous system or the peripheral autonomic neurons. Dopamine acts as a false neurotransmitter in their noradrenergic neurons. Neonates with DBH deficiency have had episodic hypothermia, hypoglycemia, and hypotension, but survivors sometimes cope relatively well until late childhood when overwhelming orthostatic hypotension profoundly limits their activities. The hypotension may be so severe that clonic seizures supervene. Most currently recognized patients are young or middle-aged adults. The diagnosis is established by the observation of severe orthostatic hypotension in a patient whose plasma norepinephrine/dopamine ratio is much less than one.

Alternative catecholamine pathways after tyrosine hydroxylase inhibition in malignant pheochromocytoma

A suppression of norepinephrine, epinephrine, and its metabolites in malignant pheochromocytoma by metyrosine was associated with an increase in tyrosine, plasma DOPA, and sulfate esters of DOPA and dopamine, followed, with continuing metyrosine administration, by a further rise of both DOPA sulfate and dopamine sulfate. Urinary dopamine progressively increased in the course of metyrosine treatment, and this, along with the increase of the dopamine metabolite, dihydroxyphenylethanol, and plasma dopamine sulfate, occurred in the absence of any change in plasma dopamine. The octopamine metabolite para-hydroxyphenylglycol, which was initially elevated at least 10-fold, also increased after metyrosine treatment. The unexpected increase of DOPA (progressively more converted toward DOPA sulfate) in the presence of tyrosine hydroxylase inhibition and increase in tyrosine may result from channeling the excess tyrosine toward DOPA and melanin through tyrosinase. Increases in plasma dopamine sulfate and urinary dopamine suggest that dopamine sulfate may be generated via DOPA sulfate and urinary dopamine may originate from circulating DOPA. Tyrosine hydroxylase inhibition may thus result in DOPA generation in non-catecholamine-producing tissues by an alternative pathway. The resulting progressive increase in DOPA and its sulfate may lead to increased urinary dopamine. DOPA sulfate may be an alternative source of dopamine sulfate.

Recent developments in the diagnosis and treatment of pheochromocytoma

The investigation and management of pheochromocytoma have been of special interest at the Mayo Clinic since 1926, when Dr. C. H. Mayo successfully removed an adrenal tumor. Recent clinical developments include the detection of asymptomatic paroxysms of hypertension by 24-hour ambulatory monitoring, detailed characterization of catecholamine cardiomyopathy by echocardiography, and further experience with Carney's triad and other polyglandular and multiple neoplasia syndromes associated with pheochromocytoma. Refinement in interpretation of catecholamine measurements and the development of radionuclide scanning with m-[131I]iodobenzylguanidine, computed tomography, and magnetic resonance imaging have greatly enhanced our diagnostic acumen. Developments in antihypertensive drug therapy and chemotherapy have improved our management of cathecholamine hypersecretion and tumor growth, respectively, in inoperable patients and in the preparation of patients for anesthesia and surgical treatment. Flow cytometry to detect abnormal DNA histograms may prove particularly useful in predicting the malignant nature of the tumors.

Treatment of infantile spasms with methysergide and alpha-methylparatyrosine

Twenty-four newly diagnosed and previously untreated infantile spasm patients were treated for 3 weeks with either methysergide (12 patients) or alpha-methylparatyrosine (12 patients). Response to therapy was determined objectively with 24-h polygraphic/video monitoring techniques and was defined as cessation of spasms and disappearance of the hypsarrhythmic EEG pattern. Two (17%) of the patients treated with alpha-methylparatyrosine responded to therapy, and one (8%) of the methysergide-treated group showed a response.

Continuous intracerebroventricular infusion of dopamine and dopamine agonists through a totally implanted drug delivery system in animal models of Parkinson's disease

We studied the effect of intracerebroventricular infusion of dopamine and dopamine agonists in animal models of dopamine deficiency as an experimental approach to the treatment of levodopa induced fluctuations in Parkinson's disease. Dopamine deficiency was produced in rats by unilateral lesion of the nigrostriatal pathway or by chronic treatment with reserpine. Monkeys were lesioned by intravenous injection of MPTP. The animals were treated with intracerebral infusions of dopamine (with or without associated intraperitoneal administration or intracerebroventricular infusion of pargyline), lisuride and pergolide. The intracerebroventricular infusion of these drugs was performed with osmotic minipumps in rats and with infusaid pumps in the monkeys. The infusion of dopamine or dopamine agonists in rats with unilateral lesions by 6-OH-dopamine produced a persistent rotation contralateral to the lesioned and implanted side. The infusion of dopamine reversed reserpine-induced akinesia only when pargyline was associated. In the range of concentration used, maximum allowed by solubility of compounds, the effects of dopamine were more potent than those of the agonists. In spite of the stability of dopamine "in vitro" when dissolved in antioxidants and at low pH, a pigment, product of autooxidation, was found in the brains of the animals infused with dopamine. The monkeys were implanted with infusaid pumps and infused for up to 3 weeks. The pump was not well tolerated due to its huge size for the animals. One monkey showed reversal of the MPTP-induced akinesia while the other, whose catheter had moved from the correct implantation site, remained unchanged. In both monkeys there was evidence of autooxidation of dopamine. Intracerebral infusion of dopamine agonists may be a possible experimental alternative to the treatment of levodopa induced fluctuations in Parkinson's disease but stable and soluble dopamine agonists and suitable delivery systems are needed.

[Alpha-methyl-paratyrosine in the treatment of malignant pheochromocytoma]

Alpha-methyl-paratyrosine (Demser) is a specific inhibitor of tyrosine hydroxylation to dopa. It is administered orally and may be given in combination with symptomatic treatments to reduce the hypersecretion of catecholamines. We report two cases of malignant phaeochromocytoma in which this drug was used. A pharmacological study of the compound is presented, and the literature on its long-term use in the treatment of malignant phaeochromocytoma is reviewed. In our second patient, who received alpha-methyl-paratyrosine for 9 months, a study of changes in differential catecholamine excretion showed that the urinary catecholamines were redistributed, with an increase in the dopamine/norepinephrine ratio. An HPLC study of urinary excretion of catecholamines demonstrated that their levels cannot be significantly increased by excretion of alpha-methyl-paratyrosine or its metabolites.

Metastatic pheochromocytoma in pregnancy and fetal biophysical assessment after maternal administration of alpha-adrenergic, beta-adrenergic, and dopamine antagonists

Metastatic pheochromocytoma, a rare complication of pregnancy, was managed from 30 weeks' gestation until delivery three weeks later with a combination of alpha-adrenergic blockade (Minipres) beta-adrenergic blockade (Timolol), and dopamine synthesis inhibition (Demser). The biophysical parameters of fetal heart rate (FHR) baseline, variability, and reactivity, as well as fetal breathing movements, body movements, tone, and amniotic fluid volume were followed sequentially during this period. A 1450-g growth-retarded infant, who subsequently did well, was delivered by cesarean section; the mother received combined surgical and medical therapy for her metastatic disease in the postpartum period. The initial fetal biophysical alteration observed was a reduction in mean FHR baseline rate; further biophysical test abnormalities appeared only after overt fetal compromise was evident. Sequential multiple parameter biophysical testing in such circumstances appears to be a valid and valuable approach to antepartum management.

alpha-Methyltyrosine blocks methylamphetamine-induced degeneration in the rat somatosensory cortex

Neurochemical and histological studies suggest that methylamphetamine (MA) administered continuously or in high doses is toxic to dopaminergic and serotonergic nerve terminals. Degeneration of the dopaminergic or serotonergic cell bodies themselves has not been reported, however. In the present study, administration of a single 100 mg/kg dose of MA was toxic to a subpopulation of neurons in the somatosensory cortex, an area of the brain which does not contain catecholaminergic or serotonergic cell bodies. This dose of MA also produced a long-lasting depletion of serotonin (5-HT) but not norepinephrine in the somatosensory cortex. Dopamine levels in the somatosensory cortices of control animals were virtually undetectable and therefore were not studied further. Administration of alpha-methyltyrosine (alpha-MT), a catecholamine synthesis inhibitor, prior to the injection of MA blocked both the depletion of 5-HT and the degeneration of cortical perikarya produced by MA alone. Since the MA-induced depletion of 5-HT and the MA-induced degeneration of cortical perikarya are correlated, we suggest that the serotonergic system may be involved in the toxic effects of MA on the cortical neurons.

Pharmacologic probes of neurotransmitter systems in tardive dyskinesia: implications for clinical management

Despite the plethora of clinical drug trials in tardive dyskinesia, few consistent findings have emerged. One possible reason for this is that there have been no serious attempts to define the role of major neurotransmitter systems (dopamine, norepinephrine, acetylcholine, serotonin, GABA) in one specific population of tardive dyskinesia patients. This study reports a series of five controlled drug trials in a population of patients with persistent tardive dyskinesia; each drug probed one of four neurotransmitter systems. The intra- and interpatient responses are analyzed and the implications of the pharmacologic response profiles for the clinical management of tardive dyskinesia are discussed.

Acute dystonia induced by neuroleptic drugs

About 2.5% of patients treated with neuroleptic drugs develop acute dystonia within 48 h of commencing therapy. The symptoms remit on drug withdrawal or following anticholinergic therapy. Acute dystonia can also be reliably induced in many primate species by neuroleptic treatment with comparable time course, symptomatology and pharmacological characteristics to those observed in man. In general, New World monkeys appear more susceptible to acute dystonia than Old World primates. It is at present not clear whether all primates, including man, would exhibit dystonia if a sufficiently high dose of neuroleptic was administered. Alternatively, some unknown, possibly species-specific or even genetic, factors may determine an individual's susceptibility to develop dystonia. Use of a rodent model of dystonia might enable more detailed analysis of biochemical correlates of dystonic behaviour. Whilst rodents do not exhibit overt dystonic behaviour after neuroleptic treatment, they may develop oral dyskinesias which bear a close pharmacological similarity to dystonia in man and primates. However, it is not known whether chewing induced by neuroleptic drugs in rats resembles acute dystonia in primates or whether this is another movement disorder possibly unique to rodent species. The pathophysiology of acute dystonia remains unknown, but may involve striatal dopaminergic and cholinergic function. In view of the close similarity between dystonia in man and other primates, studies on the mechanisms whereby neuroleptic drugs cause acute dystonic reactions in monkeys may give some clues to the pathogenesis of spontaneous dystonia in man.

Perioperative management of a patient with a malignant pheochromocytoma

A case report is presented of a patient with a known malignant pheochromocytoma, who was to undergo an orthopaedic procedure using methylmethacrylate bone cement. Preoperative preparation of the patient included the use of prazosin and metyrosine. Epidural blockade was chosen as the anaesthetic technique for intraoperative management. Surgical fixation with methylmethacrylate did not produce profound or prolonged hypotension despite sudden massive blood loss prior to its use. Epidural morphine was administered for postoperative pain control.

A therapeutic approach to tardive dyskinesia

An approach to treating tardive dyskinesia and tardive akathisia was tested in 33 patients. The common denominator was the elimination of antipsychotic drugs. In 7 of 8 patients with mild tardive dyskinesia and no akathisia who were treated by drug abstinence, gradual lessening of tardive dyskinesia occurred. Complete remission was seen after 2-4 years in 5 of these 8. Treatment with reserpine and discontinuance of antipsychotic drugs was useful for patients with severe symptoms of tardive dyskinesia or akathisia; complete remission with elimination of all drugs was achieved in 4 of 19 treated patients, without recurrence of symptoms. Although tetrabenazine masked symptoms in 5 of 7 patients to whom it was administered, none was able to achieve remission of tardive dyskinesia when taken off the drug. Seven of the total 33 patients received a course of levodopa; 2 of these 7 developed recurrence of their underlying psychosis. This agent should be used with caution.

[Malignant pheochromocytoma. A case]

A case of malignant phaeochromocytoma is reported. The primary tumour was removed in 1970. Metastases were diagnosed in 1979 and management of the condition included antihypertensive treatment with alphamethylparatyrosine, antitumoral chemotherapy and surgical reduction of secreting tissue. In these rare tumours malignancy can only be confirmed by metastases, i.e. presence of chromaffin cells in loci where they are not usually found. Histology is of little value. High levels of catecholamine precursors or their metabolites in the urine may be a sign of malignancy, but some asymptomatic tumours are only revealed by metastases. Computerized tomography and radioisotope scanning with I131 metaiodobenzylguanidine are the best available methods to locate the lesions. In view of the small number of cases and of the unpredictable course (sometimes spread over many years) of malignant phaeochromocytomas, the effectiveness of treatments with alphamethylparatyrosine, chemotherapy and radiotherapy is difficult to evaluate.

Catecholamine-secreting infratemporal fossa paraganglioma

Extraadrenal paragangliomas are tumors of the paraganglion system, usually arising from the carotid bodies, the glomus jugulare, or the glomus tympanicum. These tumors are capable of secreting catecholamines which can cause severe hypertensive crises. This paper reports a case of a patient who suffered a cerebral vascular accident due to hypertension resulting from a catecholamine-secreting infratemporal fossa paraganglioma. Any patient with a history of paroxysmal hypertension, headaches, and palpitations should be evaluated for a catecholamine-secreting tumor. Diagnosis and management of these tumors is best accomplished by a team including a radiologist, an endocrinologist, an anesthesiologist, a pathologist, an otolaryngologist--head and neck surgeon, and when the tumor invades the cranial cavity, a neurosurgeon. In this case, precise radiographic mapping of the tumor extent and its blood supply, control of hypertension with adrenergic blocking agents, and depletion of catecholamine stores using alpha-methyl-p-tyrosine allowed total extirpation through a craniofacial approach and a successful outcome.

Pheochromocytoma resistant to alpha-adrenergic blockade

In a 54-year-old man with a norepinephrine-secreting pheochromocytoma, resistance developed to the alpha-adrenergic blocking agent, phenoxybenzamine hydrochloride. Dosages of 240 mg/day were ineffective. Intravenous phentolamine mesylate reduced his BP at first, but resistance developed to this also. Therapy with alpha-methylparatyrosine, an inhibitor of catecholamine biosynthesis, finally controlled his BP, and the tumor was removed.

Pheochromocytoma: diagnosis, localization, and treatment

Pheochromocytoma is curable in 90% of cases, yet its diagnosis and localization are among the most challenging problems in clinical medicine. Although only 10% of these tumors are malignant, others may be lethal because of excessive circulating catecholamines. The clinical hallmark of pheochromocytoma is hypertension, but some patients are normotensive and may even be hypotensive.

Long-term treatment of tardive dyskinesia with presynaptically acting dopamine-depleting agents

Fourteen patients with TD, all but one also having tardive akathisia, were evaluated on presynaptically acting dopamine-depleting drugs, reserpine, TBZ, and AMT. Initially, the drugs were evaluated individually, but later AMT was used in combination with reserpine and with TBZ, since their different mechanisms of action allowed for increased potency when they were used in this combination. All but one patient responded to this therapeutic approach. Parkinsonism was easily induced, however. Most patients varied during the day between mild parkinsonism and mild dyskinesia-akathisia. It was difficult to have patients at the normal level between these two conditions. The addition of carbidopa/levodopa in one patient not only relieved the side effect of parkinsonism but may have also accelerated a remission from TD and akathisia. Although postural hypotension was a common adverse effect in patients receiving reserpine, especially in combination with AMT, it did not develop in patients taking TBZ, either alone or in combination with AMT. This observation suggests that TBZ may be less effective depleting monoamines in the periphery than in the central nervous system. Since reserpine is available commercially in the United States whereas TBZ is not, reserpine may be the drug of choice in treating patients with TD or tardive akathisia. The addition of AMT will increase the potency of this form of treatment.

Alpha methylparatyrosine and tetrabenazine in movement disorders

Clinical and experimental evidence suggests that alpha methylparatyrosine (AMPT), an inhibitor of tyrosine hydroxylase, can potentiate the effects of other dopamine antagonists. We therefore treated patients having various forms of dystonia and chorea with tetrabenazine (TBZ), and then added AMPT to determine if further improvement could be obtained. Side effects of both drugs were common, and they often necessitated withdrawal of the drug. Patients with Huntington's chorea and tardive dyskinesia were improved by TBZ. They obtained additional benefit from the combination of AMPT and TBZ. The results in the dystonia patients were disappointing with both drugs. Although a small number of patients did improve, and short- and long-term remissions occurred in a few, most patients with dystonia were not benefited by either drug.

Use of metyrosine in the anaesthetic management of patients with catecholamine-secreting tumours. A case report

Metyrosine 1.5 g daily for days decreased 24-h urine metanephrine concentration by about 60% in a patient with multiple catecholamine-secreting paragangliomas. Despite the considerable inhibition of catecholamine synthesis, this patient exhibited stress-induced sympathetic overactivity, indicated by increases in arterial pressure and serum catecholamine and urine metanephrine concentrations. It is concluded that metyrosine should be introduced early to the preoperative regimen. In this way, optimal inhibitory effect on catecholamine synthesis can be obtained and maintained for a sufficient time to allow catecholamine stores to become as close to normal as possible. Attainment of the optimal therapeutic effect is not clearly defined, but would seem to be best gauged by a combination of clinical tests of sympathetic responses and of suppression of urinary excretion of metanephrines or VMA.

alpha-Methyl-p-tyrosine: a review of its pharmacology and clinical use

alpha-Methyl-p-tyrosine is an orally active inhibitor of catecholamine synthesis which inhibits the hydroxylation of tyrosine to dopa. At dosages of 600 to 3500 mg daily it is effective in controlling the hypertensive episodes and symptoms of catecholamine excess in phaeochromocytoma during preparation for surgery. Limited published experience suggests that it is effective in controlling hypertension and symptoms in malignant phaeochromocytoma, but further long term experience is needed. Concomitant administration of phenoxybenzamine and propranolol may be desirable in some patients and treatment with phentolamine is usually necessary to control hypertension during manipulation of the tumour.

Neuroleptic-potentiating effect of alpha-methyl-p-tyrosine compared with haloperidol and placebo in a double-blind cross-over trial

The hypothesis that schizophrenia results from overactive dopaminergic influences suggests that reducing dopamine synthesis may increase the clinical effects of dopamine receptor blocking neuroleptic drugs. The neuroleptic potentiating role of alpha-methyl-paratyrosine (AMPT), a tyrosine hydroxylase inhibitor, was compared with haloperidol and placebo in a double-blind cross-over trial. Both AMPT and haloperidol increased the anti-schizophrenic effect of neuroleptic treatment in reduced dose compared with placebo (P less than 0.05), though two patients relapsed during the AMPT period. Both drugs slightly increased extrapyramidal symptoms, but the effect was greater with haloperidol. The limited antipsychotic effect and the potential for aggravating neurological symptoms suggest that the combination of AMPT and neuroleptics does not offer a superior advantage to treating schizophrenia. AMPT, however, may still be used as a research tool in elucidating pathogenetic mechanisms.

Huntington's disease: current concepts of therapy

Huntington's disease (Huntington's chorea), a degenerative disorder of the central nervous system, is inherited in an autosomal dominant pattern. Since there is no cure for this genetic disorder, therapy has been focused on pharmacologic manipulation of the involved neurotransmitter systems. In Huntington's disease, there is a functional predominance of striatal dopaminergic activity over antagonist cholinergic and possibly GABA-minergic systems. Many dopaminergic antagonists and cholinergic and GABA-minergic agonists are currently used in treatment. Supportive psychiatric care for affected persons and their families is an important therapeutic adjunct in the management of Huntington's disease. The eventual therapy will depend upon accurate identification of the primary genetic defect.

Antihypertensive activity of metyrosine in spontaneously hypertensive rats and its enhancement by carbidopa

1. Metyrosine (l-α-methyl-p-tyrosine, Demser), an inhibitor of tyrosine hydroxylase, has moderate antihypertensive activity in spontaneously hypertensive rats (20–40 mmHg fall in mean arterial pressure) at 20–80 mg/kg intraperitoneally or 80 mg/kg orally. The maximal effect is reached at 4 h after treatment and the duration of action exceeds 12 h.

2. A peripheral inhibitor of amino acid decarboxylase, carbidopa ([—]-l-α-hydrazino-3,4-dihydroxy-α-methylbenzenepropanoic acid monohydrate), (25 mg/kg intraperitoneally) has little or no antihypertensive activity alone but if administered 5 min before metyrosine, it greatly enhances the antihypertensive potency of metyrosine. The relative potency of metyrosine + carbidopa (both intraperitoneally), as compared with metyrosine alone, was 74 with 95% confidence limits of 31 and 142.

3. In another series of experiments, the antihypertensive activity of metyrosine (80 mg/kg orally) was enhanced and prolonged by carbidopa, (25 mg/kg intraperitoneally). This effect was independent of the interval between administration of the two drugs (5 or 45 min).

4. Metyrosine (20 mg/kg intraperitoneally), reduced brain and heart noradrenaline concentrations in spontaneously hypertensive rats as determined 6 h after treatment. Carbidopa (25 mg/kg intraperitoneally) slightly enhanced the noradrenaline-depleting effect of metyrosine in the whole brain but not in the heart.

5. After metyrosine or carbidopa + metyrosine, low concentrations of α-methyldopamine were found in the brain of spontaneously hypertensive rats. Methyldopa at the same dose (20 mg/kg intraperitoneally) produced a 10 times greater increase in α-methyldopamine concentrations.

6. The inhibition by carbidopa of noradrenaline synthesis in sympathetic nerve endings in the heart and in peripheral blood vessels may be at least partially responsible for the carbidopa-induced enhancement of the antihypertensive action of metyrosine.

[Preventive effect of inhibitors of catecholamine synthesis, serotonin and adrenoblockaders on anovulatory syndrome development in neonatally androgenized rats. 2]

Administration to female rats of 250 micrograms of testosterone propionate (TSP) on the 3rd day of postnatal life led to reduction of estradiol, progesterone, and, to a lesser degree, of lutropin in the blood plasma of these animals at the age of 3 months. There was an increase of the lutropin content in the adenohypophysis and of luliberin in the hypothalamus. Combined with TSP administration of alpha-methyl-p-tyrosine, p-chlorphenylalanine or droperidol promoted preservation of cyclic changes in the hypothalamic gonadotropin activity and partially prevented disturbances of estradiol and progesteron secretion caused by neonatal androgenization. The mechanisms of participation of biogenic monoamines in sex differentiation of the hypothalamus are discussed.

[Preventive action of catecholamine and serotonin synthesis inhibitors and of adrenergic blockaders on the occurrence of the anovular syndrome in neonatally androgenized rats. I]

Administration of catecholamine synthesis inhibitors (alpha-methl-p-tyrosine) or serotonin (parachlorphenylalanine) simultaneously with testosterone propionate prevented the anovular sterility in the majority of the neonatally androgenized rats. Preventive action of adrenoblockers (droperidol and propranolol) on the effects of early androgenization were weak. The data obtained pointed to the participation of catecholamines and serotonin in the realization of the masculinizing action of androgen on the neuroendocrine centres of the gonadotropin hormones secretion control.

Barbiturate physical dependence in mice: effects of neuroleptics and diazepam on the withdrawal syndrome

Diazepam (8 mg/kg) quickly and effectively reduced the incidence of withdrawal symptoms in phenobarbital dependent C57BL/6J male mice. In contrast, the neuroleptic agents employed (chlorpormazine, haloperidol, or reserpine) or alpha-methyl-p-tyrosine tended to exacerbate the withdrawal syndrome. Chlorpromazine and haloperidol were approximately equally potent in their effects; this would suggest that their antidopaminergic effects were not the primary mechanism of action for the increased incidence of withdrawal symptoms.

Cyclic AMP in cerebrospinal fluid of manic and depressive patients

Cyclic 3',5'-adenosine monophosphate (c-AMP) was measured in cerebrospinal fluid (CSF) of manic and depressive patients with and without probenecid administration both before and during treatment with various psychotropic drugs. Oral probenecid (100 mg/kg) produced substantial c-AMP accumulations in CSF suggesting a probenecid-sensitive transport mechanism for c-AMP. Baseline and probenecid-induced accumulations of c-AMP were not significantly different in manic and depressed patients, while baseline levels in depressed patients were higher than those in neurological controls. Imipramine, amitriptyline, lithium, tryptophan, and electroconvulsant therapies did not significantly alter levels or accumulations of c-AMP in CSF of depressed patients.

Avasucular necrosis of pheochromocytoma followed by spontaneous remission

Following an acute spontaneous hypertensive crisis and shock a patient with pheochromocytoma was found to have an exceedingly high catecholamine excretion rate. After this episode, the patient remained normotensive and urinary excretion of catecholamines returned to normal. During surgery, a large pheochromocytoma was found and removed that showed avascualr necrosis. In phenochromocytoma, a sudden and exceedingly high rate of catecholamine release may cause intense vasoconstriction both generally and within the tumor itself. In this patient, avascular tumor necrosis led to a spontaneous remission of clinical symptoms.

Childhood pheochromocytoma: treatment with alpha methyl tyrosine for resistant hypertension

A 12-year-old boy with a norepinephrine-secreting pheochromocytoma that caused hypertension resistant to oral alpha adrenergic blockade is reported. Resistance to alpha adrenergic blocking agents developed when the patient's daily propranolol dosage was lowered from 10 to 1 mg/kg. Subsequently, alpha methyl tyrosine, an inhibitor of tyrosine hydroxylase, the rate-limiting enzyme in catecholamine biosynthesis, controlled the patient's blood pressure and was associated with reduction in total urinary catecholamine excretion. Norepinephrine content of the tumor and uninvolved adrenal gland removal at surgery was reduced. These findings confirm that alpha methyl tyrosine inhibited in vivo synthesis of catecholamines.

The relationship between parkinsonism and tardive dyskinesia

The author analyzes parkinsonism and hyperkinesia in psychiatric patients with tardive dyskinesia before and during treatment with alpha-methyl-p-tyrosine (AMPT, a dopamine antagonist), biperiden (an acetylcholine antagonist), and baclofen (a GABA agonist); and in patients with paralysis agitans and L-dopa-induced hyperkinesia. AMPT and baclofen had similar influences on oral dyskinesia, resulting in reduced frequency, unchanged or slightly reduced amplitude, and increased duration of each movement. The author concludes that: 1) reduced dopaminergic activity may be the primary pathogenetic background for tardive dyskinesia; 2) dopaminergic hypersensitivity and/or cholinergic hypofunction is necessary before hyperkinesia breaks through; and 3) the neurotoxic effects of neuroleptics may be associated with age-dependent changes in nigrostriatal regions representing oral innervation.