Biomedical subjects
Publications and source records attributed to D B Calne.
A method for measuring hydroxylase cofactor activity in human cerebrospinal fluid is described. The hydroxylase cofactor content of cerebrsopinal fluid from Parkinsonian patients is approximately 50 percent that of normal subjects. A significant correlation between hydroxylase cofactor and the concentration of homovanillic acid in the cerebrospinal fluid was observed.
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Continuous intravenous infusion of levodopa was used for eight days to manage a parkinsonian patient with "on-off" fluctuations who underwent abdominoperineal resection for carcinoma of the rectum. Reasonable control of parkinsonism was obtained initially with small doses of levodopa, but more than 4 g daily were eventually required. No adverse effects on cardiac rhythm, blood pressure, or gastrointestinal function occurred. Frequent adjustment of levodopa dosage was necessary in view of continuing "on-off" fluctuations. Severe akinesia, which can cause dysphagia, respiratory complications, and venous stasis in the legs, can benefit from this method of management after major abdominal surgery in a patient with advanced parkinsonism.
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Because of the high concentrations of gamma-aminobutyric acid (GABA) in the cerebellar cortex and nuclei, an attempt was made to enhance GABAergic transmission in patients with cerebellar disease. Maximum tolerated doses of sodium valproate, a drug which inhibits the degradation of GABA, failed to influence cerebellar deficits in a double blind crossover study on six patients.
Because there is biochemical evidence of decreased GABAergic function in Parkinson's disease, sodium valproate, an inhibitor of GABA catabolism, was administered to eight Parkinsonian patients. Valproate treatment did not significantly alter any Parkinsonian feature, but tended to increase the dyskinesia in the "on-off" patients. The increased dyskinesias were not a result of altered peripheral metabolism of L-dopa. Despite obtaining high plasma levels of valproate, no consistent alteration of CSF GABA levels could be demonstrated. Thus, in these patients, an effect of valproate on GABA metabolism is unproven, and in turn, the role of GABA in Parkinsonism and dyskinesia uncertain.
While the era of major advances in understanding and treating parkinsonism seems to be over, steady progress is being made in elucidating physiological and pharmacological aspects of extrapyramidal function. The dramatic impact of levodopa therapy has been followed by the recognition of serious limitations to its long-term use, which provides a continuing stimulus for efforts to analyze the physiological and pharmacological properties of the basal ganglia and substantia nigra. There are reasonable grounds for the hope that this research will lead to significant developments in therapy.
Eight out of 12 unselected patients with Shy-Drager syndrome were found to have severe bilateral paresis of vocal cord abduction by fibre-optic laryngoscopy. This commonly presented as increased snoring followed by episodes of inspiratory and expiratory stridor and sometimes by sleep apnoea. Respiratory failure eventually developed in four cases and was reversed by tracheostomy. In another patient tracheostomy relieved severe attacks of sleep apnoea. This complication was not necessarily associated with advanced disease, and it should be considered in all patients with Shy-Drager syndrome as appropriate treatment can lead to a useful extension of life.
Two recent sporadic cases of progressive Parkinsonism after encephalitis are described. Both patients had two oligoclonal protein bands in their CSF. These bands were not present in patients with idiopathic Parkinson's disease and might, therefore, be useful for diagnostic purposes, particularly when the history of encephalitis is uncertain.
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Advances through basic research have elucidated the disturbances of neurotransmitter function in Parkinson's Dopamine has replaced acetylcholine and norepinephrine as the most studied neurotransmitter, with both conceptual and practical developments, exemplified by the hypothesis of cyclic adenosine monophosphate as a "second messenger," and new therapeutic agents. We now have rationally designed in-vitro and in-vivo tests for the evaluation of dopaminergic compounds instead of entirely empiric screening procedures. We are starting to identify different categories of dopaminergic receptors and to manipulate them selectively, with gains in understanding the physiologic input to the striatum. Crucial questions remain, including how dopamine modulates striatal output and what causes the parkinsonian degeneration of the nigrostriatal pathway. Developing knowledge on synaptic physiology and pharmacology may lead to better therapy.
Increased serum activities of the enzymes alanine aminotransferase (ALT) and aspartate aminotransferase (AST) occurred in 12 out of 19 patients with idiopathic parkinsonism when they were treated with the ergot derivative lergotrile at an oral dose varying from 50 to 150 mg daily. Hepatocellular injury was confirmed by microscopic examination of liver biopsies obtained from 3 of these patients when the serum activities of ALT and AST were appreciably elevated. Light microscopy revealed features of mild acute hepatocellular injury, and electron microscopy showed proliferation of the smooth endoplasmic reticulum and apparently unique mitochondrial changes in hepatocytes. This is the first report of pathological changes in the liver associated with the therapeutic use of an ergot derivative. The presence of a potentially reactive cyanide group in the lergotrile molecule could be causally related to the observed hepatocellular injury. It is suggested that serum ALT and AST activities should be monitored carefully when the therapeutic potential of any new ergot derivative is assessed.
The response of Parkinsonism to three ergot derivatives which modify dopaminergic transmission was studied. CF 25-397 behaved more as an antagonist than an agonist. Lergotrile was an agonist with therapeutic properties marred by prominent hepatotoxicity. Bromocriptine is an effective anti-Parkinsonian agent, particularly useful in patients with prominent dyskinesia or "on-off" reactions to levodopa; in most patients optimal results have been obtained by combining from 40 to 90 mg of bromocriptine daily with approximately 60% of the previous maximal dose of levodopa. Unfortunately, only some 50% of patients tolerate long-term bromocriptine therapy, but all adverse reactions have been dose dependent and reversible.
92 patients with parkinsonism have been treated with bromocriptine for up to 30 months. 48 continue to receive bromocriptine with benefit; of these, 35 take bromocriptine (mean dose 53 mg daily) in combination with levodopa and 13 take bromocriptine (mean dose 45 mg daily) without levodopa. In those who were originally on levodopa, addition of bromocriptine allowed a mean 41% reduction in the dose of levodopa; the largest group of patients to benefit from bromocriptine entered the study because of excessive dyskinesia or "on-off" phenomena induced by levodopa. In 40 patients bromocriptine was stopped because of adverse reactions, absence of therapeutic response, or non-compliance with the protocol. The main problems were psychiatric disturbance (8 patients) and erythromelalgia (7 patients); these effects tended to occur late (mean 6 months and 10 months, respectively) and with high dosage (mean 66 mg and 115 mg daily). Other frequent adverse effects were dizziness and nausea; these began considerably earlier (at 2 months and 1 month) and with much lower dosage (31 mg and 12 mg daily). 4 patients died, for reasons apparently unrelated to therapy.
Animal experiments suggest that opiate peptides might play a role in extrapyramidal function. This hypothesis was tested by administering the opiate antagonist, naltrexone, in doses sufficient to antagonize exogenous opiates, to patients with parkinsonism and Huntington's disease. No improvement in the clinical features of either disorder was noted.
The therapeutic and adverse effects of two ergot derivatives, bromocriptine and lergotrile, were compared in idiopathic parkinsonism. At both low (50 mg daily) and high (150 mg daily) dosage there was a similar but not identical profile of response. Initially, lergotrile tended to induce more severe but always transient hypotension. At higher doses, bromocriptine caused more dyskinesia. Neurological deficits improved with increasing doses up to an average daily level of 80 to 150 mg of ergot derivatives combined with levodopa, 450 to 1,150 mg, and carbidopa, 45 to 115 mg. However, efficacy often declined at the highest doses of antiparkinsonian agents. Adverse effects caused by ergot derivatives are more common with dosages greater than 100 mg per day. In general, the best overall therapeutic results with bromocriptine and lergotrile were obtained in the dose range of 50 to 100 mg daily for each. It is concluded that bromocriptine and lergotrile are similar in their therapeutic properties and that both are comparable in efficacy to levodopa plus carbidopa (though optimal results are commonly obtained by combining submaximal doses of levodopa with ergot derivatives). The role for each drug in the treatment of parkinsonism is likely to be determined by factors such as cost (bromocriptine) and hepatotoxicity (lergotrile).
While the etiology of the most common form of parkinsonism (idiopathic) remains elusive, studies of the regional biochemistry and pharmacology of the brain have led to recognition of the importance of certain pathways, such as the nigrostriatal system. This information evolved from the discovery that the neurotransmitter dopamine is depleted in parkinsonism and that restoration of dopamine by administration of its precursor, levodopa, induces a dramatic therapeutic response in many patients. Such studies have initiated and sustained a major surge in neuropharmacologic advances, but the tangible benefits, in the form of therapeutic results, have undergone some critical reappraisal with the appearance of late adverse reactions to levodopa. One practical approach to this problem is deliberate delay in starting levodopa therapy and the use of lower doses. Use of artificial dopaminergic agonists and selective inhibitors of monoamine oxidase B has also been investigated.
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