[ADDITIONAL EXPERIMENTAL STUDIES ON L-DOPA IN PARKINSON'S SYNDROME AND RESERPINE PARKINSONISM]

The Potential of Metabolomics to Find Proper Biomarkers for Addressing the Neuroprotective Efficacy of Drugs Aimed at Delaying Parkinson's and Alzheimer's Disease Progression

The first objective is to highlight the lack of tools to measure whether a given intervention affords neuroprotection in patients with Alzheimer's or Parkinson's diseases. A second aim is to present the primary outcome measures used in clinical trials in cohorts of patients with neurodegenerative diseases. The final aim is to discuss whether metabolomics using body fluids may lead to the discovery of biomarkers of neuroprotection. Information on the primary outcome measures in clinical trials related to Alzheimer's and Parkinson's disease registered since 2018 was collected. We analysed the type of measures selected to assess efficacy, not in terms of neuroprotection since, as stated in the aims, there is not yet any marker of neuroprotection. Proteomic approaches using plasma or CSF have been proposed. PET could estimate the extent of lesions, but disease progression does not necessarily correlate with a change in tracer uptake. We propose some alternatives based on considering the metabolome. A new opportunity opens with metabolomics because there have been impressive technological advances that allow the detection, among others, of metabolites related to mitochondrial function and mitochondrial structure in serum and/or cerebrospinal fluid; some of the differentially concentrated metabolites can become reliable biomarkers of neuroprotection.

Challenges involved in cell therapy for Parkinson's disease using human pluripotent stem cells

Neurons derived from human pluripotent stem cells (hPSCs) provide a valuable tool for studying human neural development and neurodegenerative diseases. The investigation of hPSC-based cell therapy, involving the differentiation of hPSCs into target cells and their transplantation into affected regions, is of particular interest. One neurodegenerative disease that is being extensively studied for hPSC-based cell therapy is Parkinson's disease (PD), the second most common among humans. Various research groups are focused on differentiating hPSCs into ventral midbrain dopaminergic (vmDA) progenitors, which have the potential to further differentiate into neurons closely resembling DA neurons found in the substantia nigra pars compacta (SNpc) after transplantation, providing a promising treatment option for PD. In vivo experiments, where hPSC-derived vmDA progenitor cells were transplanted into the striatum or SNpc of animal PD models, the transplanted cells demonstrated stable engraftment and resulted in behavioral recovery in the transplanted animals. Several differentiation protocols have been developed for this specific cell therapy. However, the lack of a reliable live-cell lineage identification method presents a significant obstacle in confirming the precise lineage of the differentiated cells intended for transplantation, as well as identifying potential contamination by non-vmDA progenitors. This deficiency increases the risk of adverse effects such as dyskinesias and tumorigenicity, highlighting the importance of addressing this issue before proceeding with transplantation. Ensuring the differentiation of hPSCs into the target cell lineage is a crucial step to guarantee precise therapeutic effects in cell therapy. To underscore the significance of lineage identification, this review focuses on the differentiation protocols of hPSC-derived vmDA progenitors developed by various research groups for PD treatment. Moreover, in vivo experimental results following transplantation were carefully analyzed. The encouraging outcomes from these experiments demonstrate the potential efficacy and safety of hPSC-derived vmDA progenitors for PD cell therapy. Additionally, the results of clinical trials involving the use of hPSC-derived vmDA progenitors for PD treatment were briefly reviewed, shedding light on the progress and challenges faced in translating this promising therapy into clinical practice.

The story of levodopa: A long and arduous journey

Levodopa (L-dopa) is the gold standard in the management of Parkinson's disease (PD). It dates back to 1500 to 1000 BC when it was used in the Indian Ayurvedic and Chinese system of medicine. Certain beans such as velvet beans and broad beans contain L-dopa. The plant Mucuna pruriens (Mp) or velvet bean, cultivated in Eastern India and Southern China, contains L-dopa at a concentration of 5% and was used for the management of PD. Later, workers have documented the neuroprotective, neurorestorative, and immunomodulatory properties of Mp. Double-blind studies conducted in the Western world have proved the efficacy of Mp and reported some toxic side effects as well. In the Western world, the credit for isolating L-dopa from the seeds of Vicia faba or broad bean goes to Markus Guggenheim, a biochemist from Sweden in 1913. However, it has been used with success ever since Arvid Carlsson established the reversibility of reserpine-induced akinesia in rabbits in the late 1950s with the use of intravenous dopamine, and Oleh Hornykiewicz demonstrated its deficiency in the striatum in 1960–1961. George Cotzias used it in patients in a low and slow incremental fashion in 1967, and Melvin Yahr and his colleagues performed double-blind study on in-patients with success in 1969. Complications with its long-term use, particularly the on-off phenomenon, and dyskinesias appeared soon, and measures have been undertaken to reduce their incidence. Researches on alternative modes of delivery are carried out in various centers, and others are under investigation in the laboratories.

Microglial Adenosine Receptors: From Preconditioning to Modulating the M1/M2 Balance in Activated Cells

Neuronal survival depends on the glia, that is, on the astroglial and microglial support. Neurons die and microglia are activated not only in neurodegenerative diseases but also in physiological aging. Activated microglia, once considered harmful, express two main phenotypes: the pro-inflammatory or M1, and the neuroprotective or M2. When neuroinflammation, i.e., microglial activation occurs, it is important to achieve a good M1/M2 balance, i.e., at some point M1 microglia must be skewed into M2 cells to impede chronic inflammation and to afford neuronal survival. G protein-coupled receptors in general and adenosine receptors in particular are potential targets for increasing the number of M2 cells. This article describes the mechanisms underlying microglial activation and analyzes whether these cells exposed to a first damaging event may be ready to be preconditioned to better react to exposure to more damaging events. Adenosine receptors are relevant due to their participation in preconditioning. They can also be overexpressed in activated microglial cells. The potential of adenosine receptors and complexes formed by adenosine receptors and cannabinoids as therapeutic targets to provide microglia-mediated neuroprotection is here discussed.

Genes Implicated in Familial Parkinson's Disease Provide a Dual Picture of Nigral Dopaminergic Neurodegeneration with Mitochondria Taking Center Stage

The mechanism of nigral dopaminergic neuronal degeneration in Parkinson's disease (PD) is unknown. One of the pathological characteristics of the disease is the deposition of α-synuclein (α-syn) that occurs in the brain from both familial and sporadic PD patients. This paper constitutes a narrative review that takes advantage of information related to genes (SNCA, LRRK2, GBA, UCHL1, VPS35, PRKN, PINK1, ATP13A2, PLA2G6, DNAJC6, SYNJ1, DJ-1/PARK7 and FBXO7) involved in familial cases of Parkinson's disease (PD) to explore their usefulness in deciphering the origin of dopaminergic denervation in many types of PD. Direct or functional interactions between genes or gene products are evaluated using the Search Tool for the Retrieval of Interacting Genes/Proteins (STRING) database. The rationale is to propose a map of the interactions between SNCA, the gene encoding for α-syn that aggregates in PD, and other genes, the mutations of which lead to early-onset PD. The map contrasts with the findings obtained using animal models that are the knockout of one of those genes or that express the mutated human gene. From combining in silico data from STRING-based assays with in vitro and in vivo data in transgenic animals, two likely mechanisms appeared: (i) the processing of native α-syn is altered due to the mutation of genes involved in vesicular trafficking and protein processing, or (ii) α-syn mutants alter the mechanisms necessary for the correct vesicular trafficking and protein processing. Mitochondria are a common denominator since both mechanisms require extra energy production, and the energy for the survival of neurons is obtained mainly from the complete oxidation of glucose. Dopamine itself can result in an additional burden to the mitochondria of dopaminergic neurons because its handling produces free radicals. Drugs acting on G protein-coupled receptors (GPCRs) in the mitochondria of neurons may hopefully end up targeting those receptors to reduce oxidative burden and increase mitochondrial performance. In summary, the analysis of the data of genes related to familial PD provides relevant information on the etiology of sporadic cases and might suggest new therapeutic approaches.

Dopamine in Health and Disease: Much More Than a Neurotransmitter

Dopamine is derived from an amino acid, phenylalanine, which must be obtained through the diet. Dopamine, known primarily to be a neurotransmitter involved in almost any higher executive action, acts through five types of G-protein-coupled receptors. Dopamine has been studied extensively for its neuronal handling, synaptic actions, and in relation to Parkinson's disease. However, dopamine receptors can be found extra-synaptically and, in addition, they are not only expressed in neurons, but in many types of mammalian cells, inside and outside the central nervous system (CNS). Recent studies show a dopamine link between the gut and the CNS; the mechanisms are unknown, but they probably require cells to act as mediators and the involvement of the immune system. In fact, dopamine receptors are expressed in almost any cell of the immune system where dopamine regulates various processes, such as antigen presentation, T-cell activation, and inflammation. This likely immune cell-mediated linkage opens up a new perspective for the use of dopamine-related drugs, i.e., agonist-antagonist-allosteric modulators of dopamine receptors, in a variety of diseases.

Angiotensin AT1 and AT2 receptor heteromer expression in the hemilesioned rat model of Parkinson's disease that increases with levodopa-induced dyskinesia

BACKGROUND/AIMS

The renin-angiotensin system (RAS) is altered in Parkinson's disease (PD), a disease due to substantia nigra neurodegeneration and whose dopamine-replacement therapy, using the precursor levodopa, leads to dyskinesias as the main side effect. Angiotensin AT₁ and AT₂ receptors, mainly known for their role in regulating water homeostasis and blood pressure and able to form heterodimers (AT_1/2Hets), are present in the central nervous system. We assessed the functionality and expression of AT_1/2Hets in Parkinson disease (PD).

METHODS

Immunocytochemistry was used to analyze the colocalization between angiotensin receptors; bioluminescence resonance energy transfer was used to detect AT_1/2Hets. Calcium and cAMP determination, MAPK activation, and label-free assays were performed to characterize signaling in homologous and heterologous systems. Proximity ligation assays were used to quantify receptor expression in mouse primary cultures and in rat striatal sections.

RESULTS

We confirmed that AT₁ and AT₂ receptors form AT_1/2Hets that are expressed in cells of the central nervous system. AT_1/2Hets are novel functional units with particular signaling properties. Importantly, the coactivation of the two receptors in the heteromer reduces the signaling output of angiotensin. Remarkably, AT_1/2Hets that are expressed in both striatal neurons and microglia make possible that candesartan, the antagonist of AT₁, increases the effect of AT₂ receptor agonists. In addition, the level of striatal expression increased in the unilateral 6-OH-dopamine lesioned rat PD model and was markedly higher in parkinsonian-like animals that did not become dyskinetic upon levodopa chronic administration if compared with expression in those that became dyskinetic.

CONCLUSION

The results indicate that boosting the action of neuroprotective AT₂ receptors using an AT₁ receptor antagonist constitutes a promising therapeutic strategy in PD.

Microbiota and Other Preventive Strategies and Non-genetic Risk Factors in Parkinson's Disease

The exact cause of Parkinson’s disease (PD), the second most prevalent neurodegenerative disease in modern societies, is still unknown. Many scientists point out that PD is caused by a complex interaction between different factors. Although the main risk factor is age, there are other influences, genetic and environmental, that individually or in combination may trigger neurodegenerative changes leading to PD. Nowadays, research remains focused on better understanding which environmental factors are related to the risk of developing PD and why. In line with the knowledge on evidence on exposures that prevent/delay PD onset or that impact on disease progression, the aims of this review were: (i) to comment on the non-genetic risk factors that mainly affect idiopathic PD; and (ii) to comment on seemingly reliable preventive interventions. We discuss both environmental factors that may affect the central nervous system (CNS) or the intestinal tract, and the likely mechanisms underlying noxious or protective actions. Knowledge on risk, protective factors, and mechanisms may help to envisage why nigral dopaminergic neurons are so vulnerable in PD and, eventually, to design new strategies for PD prevention and/or anti-PD therapy. This article reviews the variety of the known and suspected environmental factors, such as lifestyle, gut microbiota or pesticide exposition, and distinguishes between those that are harmful or beneficial for the PD acquisition or progression. In fact, the review covers one of the most novel players in the whole picture, and we address the role of microbiota on keeping a healthy CNS and/or on preventing the “side-effects” related to aging.

The Kinetic Component in Drug Discovery: Using the Most Basic Pharmacological Concepts to Advance in Selecting Drugs to Combat CNS Diseases

To reach the central nervous system (CNS), drugs must cross the brain-blood barrier and have appropriate pharmacokinetic/dynamic properties. However, in early drug discovery steps, the selection of lead compounds, for example, those targeting G-protein-coupled receptors (GPCRs), is made according to i) affinity, which is calculated in in vitro equilibrium conditions, and ii) potency, a signal transduction-related parameter, usually quantified at a fixed time-point in a heterologous expression system. This paper argues that kinetics must be considered in the early steps of lead compound selection. While affinity calculation requires the establishment of a ligand-receptor equilibrium, the signal transduction starts as soon as the receptor senses the agonist. Taking cAMP production as an example, the in vitro-measured cytoplasmic levels of this cyclic nucleotide do not depend on equilibrium dissociation constant, KD. Signaling occurs far from the equilibrium and correlates more with the binding rate (kon) than with KD. Furthermore, residence time, a parameter to consider in lead optimization, may significantly vary from in vitro to in vivo conditions. The results are discussed from the perspective of dopaminergic neurotransmission and dopaminereceptor- based drug discovery.

Purinergic Signalling in Parkinson's Disease: A Multi-target System to Combat Neurodegeneration

Parkinson's disease (PD) is the second most common neurodegenerative disorder, characterized by progressive loss of dopaminergic neurons that results in characteristic motor and non-motor symptoms. L-3,4 dihydroxyphenylalanine (L-DOPA) is the gold standard therapy for the treatment of PD. However, long-term use of L-DOPA leads to side effects such as dyskinesias and motor fluctuation. Since purines have neurotransmitter and co-transmitter properties, the function of the purinergic system has been thoroughly studied in the nervous system. Adenosine and adenosine 5'-triphosphate (ATP) are modulators of dopaminergic neurotransmission, neuroinflammatory processes, oxidative stress, excitotoxicity and cell death via purinergic receptor subtypes. Aberrant purinergic receptor signalling can be either the cause or the result of numerous pathological conditions, including neurodegenerative disorders. Many data confirm the involvement of purinergic signalling pathways in PD. Modulation of purinergic receptor subtypes, the activity of ectonucleotidases and ATP transporters could be beneficial in the treatment of PD. We give a brief summary of the background of purinergic signalling focusing on its roles in PD. Possible targets for pharmacological treatment are highlighted.

Therapeutic strategies for Parkinson disease: beyond dopaminergic drugs

Existing therapeutic strategies for managing Parkinson disease (PD), which focus on addressing the loss of dopamine and dopaminergic function linked with degeneration of dopaminergic neurons, are limited by side effects and lack of long-term efficacy. In recent decades, research into PD pathophysiology and pharmacology has focused on understanding and tackling the neurodegenerative processes and symptomology of PD. In this Review, we discuss the challenges associated with the development of novel therapies for PD, highlighting emerging agents that aim to target cell death, as well as new targets offering a symptomatic approach to managing features and progression of the disease.

mGlu4 allosteric modulation for treating Parkinson's disease

2017 is the 200th anniversary of the first published description of Parkinson's disease (PD). Fifty years ago, the clinical benefit of levodopa was first documented, representing the most important advance in the treatment of PD so far. Among the novel targets identified in the last decade, positive allosteric modulators (PAM) of mGlu₄ receptors show great promise, with the potential to change the paradigm of the PD treatment approach. mGlu₄ PAMs have shown consistent efficacy in various preclinical models of PD, and entered clinical trials for the first time in 2017. This review synthesizes the rationale for mGlu₄ PAM development for PD and progress to date, reporting the key achievements from preclinical studies to the first-in-class compound assessment in man.

Levodopa therapy for Parkinson disease: A look backward and forward

Although levodopa is widely recognized as the most effective therapy for Parkinson disease (PD), its introduction 5 decades ago was preceded by several years of uncertainty and equivocal clinical results. The translation of basic neuroscience research by Arvid Carlsson and Oleh Hornykiewicz provided a logical pathway for treating PD with levodopa. Yet the pioneering clinicians who transformed PD therapeutics with this drug--among them Walther Birkmayer, Isamu Sano, Patrick McGeer, George Cotzias, Melvin Yahr, and others--faced many challenges in determining whether the concept and the method for replenishing deficient striatal dopamine was correct. This article reviews highlights in the early development of levodopa therapy. In addition, it provides an overview of emerging drug delivery strategies that show promise for improving levodopa's pharmacologic limitations.

The Human Experience with Intravenous Levodopa

Objective: To compile a comprehensive summary of published human experience with levodopa given intravenously, with a focus on information required by regulatory agencies.

Background: While safe intravenous (IV) use of levodopa has been documented for over 50 years, regulatory supervision for pharmaceuticals given by a route other than that approved by the U.S. Food and Drug Administration (FDA) has become increasingly cautious. If delivering a drug by an alternate route raises the risk of adverse events, an investigational new drug (IND) application is required, including a comprehensive review of toxicity data.

Methods: Over 200 articles referring to IV levodopa were examined for details of administration, pharmacokinetics, benefit, and side effects.

Results: We identified 142 original reports describing IVLD use in humans, beginning with psychiatric research in 1959–1960 before the development of peripheral decarboxylase inhibitors. At least 2760 subjects have received IV levodopa, and reported outcomes include parkinsonian signs, sleep variables, hormone levels, hemodynamics, CSF amino acid composition, regional cerebral blood flow, cognition, perception and complex behavior. Mean pharmacokinetic variables were summarized for 49 healthy subjects and 190 with Parkinson's disease. Side effects were those expected from clinical experience with oral levodopa and dopamine agonists. No articles reported deaths or induction of psychosis.

Conclusion: At least 2760 patients have received IV levodopa with a safety profile comparable to that seen with oral administration.

Purinergic signaling in Parkinson's disease. Relevance for treatment

Purinergic signaling modulates dopaminergic neurotransmission in health and disease. Classically adenosine A1 and A2A receptors have been considered key for the fine tune control of dopamine actions in the striatum, the main CNS motor control center. The main adenosine signaling mechanism is via the cAMP pathway but the future will tell whether calcium signaling is relevant in adenosinergic control of striatal function. Very relevant is the recent approval in Japan of the adenosine A2A receptor antagonist, istradefylline, for use in Parkinson's disease patients. Purine nucleotides are also regulators of striatal dopamine neurotransmission via P2 purinergic receptors. In parallel to the alpha-synuclein hypothesis of Parkinson's disease etiology, purinergic P2X1 receptors have been identified as mediators of accumulation of the Lewy-body enriched protein alpha-synuclein. Of note is the expression in striatum of purinergic-receptor-containing heteromers that are potential targets of anti-Parkinson's disease therapies and should be taken into account in drug discovery programs. This article is part of the Special Issue entitled 'Purines in Neurodegeneration and Neuroregeneration'.

The medical treatment of Parkinson disease from James Parkinson to George Cotzias

It took exactly 150 years since James Parkinson's description in 1817 of the illness bearing his name until the development of effective therapy for this disorder, namely, the introduction of high-dosage levodopa by George Cotzias in 1967. During the first 50 years, no effective therapy was available, but neurologists reported using different agents, including metals. Then, around 1867, Charcot found solanaceous alkaloids to be somewhat helpful, and these became the accepted and popular therapy for the next 75 years. When basic scientists discovered that these alkaloids had central antimuscarinic activity, pharmaceutical chemists developed synthetic chemical agents that were equally effective, with possibly less adverse effects, and around 1950 these synthetic drugs became the standard medical therapy for Parkinson's disease (PD). The link between dopamine and PD did not take place until 1957, 140 years after Parkinson's Essay. The clue came from research on reserpine, a drug derived from the Rauwolfia plant that caused a sedative effect, now recognized as a drug-induced parkinsonian state. Initial investigations revealed that reserpine caused the release and depletion of serotonin stores in the brain. With that knowledge, Arvid Carlsson, a young pharmacologist in Sweden, decided to explore the possibility that reserpine might also affect brain catecholamines. In his now famous, elegant, and simple experiment, he showed that injecting l-dopa, the precursor of catecholamines, alleviated the reserpine-induced parkinsonian state in animals, whereas the precursor of serotonin failed to do so. Carlsson then developed a highly sensitive assay to measure dopamine, and his lab found that dopamine is selectively present in high concentrations in the striatum and that administered l-dopa could restore the dopamine depleted by reserpine. Carlsson postulated that all these findings implicate dopamine in motor disorders. Oleh Hornykiewicz, a young pharmacologist in Vienna, on being aware of the regional localization of brain dopamine, decided to measure it in the brains of people who had PD and postencephalitic parkinsonism. In 1960, he reported finding markedly depleted dopamine in the striatum in these conditions. Immediately after, Hornykiewicz teamed up with the geriatrician, Walther Birkmayer, to inject small doses of l-dopa intravenously (IV) into PD patients. They found benefit and pursued this treatment, but the gastrointestinal side effects limited the dosage, and many neurologists were doubtful that the effects from l-dopa were any better than those with antimuscarinic agents. A number of neurologists tested such low doses of IV l-dopa and even higher oral dosages, but without showing any dramatic benefit, not better than the antimuscarinics. Some of these studies were small, controlled trials. This general lack of efficacy with l-dopa prevailed, and neurologists were discouraged about l-dopa until 1967, when George C. Cotzias, a neuropharmacologist in New York, reported his results. He thought that PD may be result from the loss of neuromelanin in the substantia nigra, and he decided to try to replenish the depleted neuromelanin. Among the agents he tried was dl-dopa. He wisely began with low oral doses and increased the dosage slowly and steadily, thereby limiting the gastrointestinal complication. He also treated his patients for a long duration, months in a government-supported hospital. In the accompanying videotape of an interview Cotzias gave in 1970, he describes much of his success to be able to observe his patients over months while building up the dosage very slowly and observe for signs of toxicity. When higher doses, usually over 12 g/day, were reached, dramatic antiparkinsonian effects were observed, and a revolutionary new treatment for PD was established.

MAO-inhibitors in Parkinson's Disease

Monoamine oxidase inhibitors (MAO-I) belong to the earliest drugs tried in Parkinson's disease (PD). They have been used with or without levodopa (L-DOPA). Non-selective MAO-I due to their side-effect/adverse reaction profile, like tranylcypromine have limited use in the treatment of depression in PD, while selective, reversible MAO-A inhibitors are recommended due to their easier clinical handling. For the treatment of akinesia and motor fluctuations selective irreversible MAO-B inhibitors selegiline and rasagiline are recommended. They are safe and well tolerated at the recommended daily doses. Their main differences are related to (1) metabolism, (2) interaction with CYP-enzymes and (3) quantitative properties at the molecular biological/genetic level. Rasagiline is more potent in clinical practise and has a hypothesis driven more favourable side effect/adverse reaction profile due to its metabolism to aminoindan. Both selegiline and rasagiline have a neuroprotective and neurorestaurative potential. A head-to head clinical trial would be of utmost interest from both the clinical outcome and a hypothesis-driven point of view. Selegiline is available as tablet and melting tablet for PD and as transdermal selegiline for depression, while rasagiline is marketed as tablet for PD. In general, the clinical use of MAO-I nowadays is underestimated. There should be more efforts to evaluate their clinical potency as antidepressants and antidementive drugs in addition to the final proof of their disease-modifying potential. In line with this are recent innovative developments of MAO-I plus inhibition of acetylcholine esterase for Alzheimer's disease as well as combined MAO-I and iron chelation for PD.

The metabolism of L-m-tyrosine: the use of a putative precursor to investigate the increased production of m-hydroxymandelic acid in phenylketonuria

Several urinary meta-substituted phenols appear to be of endogenous origin. However, the production of these compounds is reduced in phenylketonuria with the exception of m-hydroxymandelic acid whose excretion is approximately doubled. This phenomenon has been investigated in two patients with phenylketonuria using the putative precursor L-m-tyrosine labelled with deuterium. Metabolism of this compound in these patients was comparable to that in healthy adults although much less was converted to m-hydroxymandelic acid and the excretion pattern of this metabolite was different. This apparent anomaly is attributed to smaller metabolic compartments in phenylketonuria and a lower threshold for the metabolism of m-tyramine via beta-hydroxylation. Incorporation into the natural pathway was shown by depletion of endogenous m-hydroxymandelic acid. The results are further support for the ideas that the amine precursors of m-hydroxymandelic acid, m-tyramine and m-octopamine, have a functional role and may be important in the pathogenesis of phenylketonuria.

Levodopa in Parkinson disease: a long-term appraisal of mortality

Mortality rates for a group of patients in a collaborative multicenter study of levodopa (Larodopa) in the treatment of parkinsonism were compared with corresponding mortality rates in the general population adjusted for age and sex distribution in accordance with that of the parkinsonian patients under study. The death rate, conservatively adjusted for dropouts among parkinsonian patients, is estimated to be approximately 33% greater than that for the general population. This is in contrast to an earlier study of Hoehn and Yahr, prior to the advent of levodopa treatment, wherein the mortality rate for parkinsonian patients was shown to be in excess of that in the general population by a factor of 2.9, or nearly 200%.

Blood pressure responses to noradrenaline and dopamine infusions in Parkinson's disease and the Shy-Drager syndrome

Studies of pulse rate and blood pressure responses to graded intravenous infusions of noradrenaline and dopamine were performed on five patients with Parkinson's disease, five with the Shy-Drager syndrome and seven healthy subject. Cardiovascular reflex responses to standing and to the Valsalva manoeuvre were found to be preserved in all patients with Parkinson's disease but to be grossly defective or absent in all with the Shy-Drager syndrome. Each subject received separate intravenous infusions of L-noradrenaline and dopamine, delivered at increasing rates, until a 30% rise in systolic blood pressure was achieved. Heart rate decreased during pressor responses to noradrenaline in control subjects and patients with Parkinson's disease, but increased in those with the Shy-Drager syndrome. Heart rate increased during pressor responses to dopamine in all subjects. Compared to control subjects supersensitivity to noradrenaline was observed both in patients with Parkinson's disease and, to a greater extent, in those with the Shy-Drager syndrome. Subsensitivity to dopamine was observed in patients with Parkinson's disease, but supersensitivity in those with the Shy-Drager syndrome.

Dopamine (3-hydroxytyramine) metabolism in parkinsonism

Three patients with idiopathic parkinsonism and six normal subjects were infused over a 4 hr period with 104.6 muc of dopamine-2-(14)C (3,4-dihydroxyphenylethylamine, 3-hydroxytyramine),(1) the immediate precursor in the synthesis of the sympathetic neurohormone, noradrenaline (norepinephrine). Urine was collected during the infusion period, 0-2 hr, 2-4 hr, 4-8 hr, 8-24 hr, and thereafter for 4 additional days. Using a technique herein described, the various metabolic and biosynthetic products of dopamine, including noradrenaline and its metabolic products, were separated, identified, and their radioactivity measured. The metabolic pattern of dopamine in the normal subject was compared to that of the three parkinsonism patients. The results indicate that in idiopathic parkinsonism there is a decrease in the recovery of free radioactive noradrenaline in the urine following an infusion of dopamine-2-(14)C and a slight shift toward dopamine metabolism. The latter is reflected by an increase in the following metabolites of dopamine: 3,4-dihydroxyphenylacetic acid and the conjugates of 3-methoxy-4-hydroxyphenylacetic acid, 3,4-dihydroxyphenylacetic acid, 3-methoxy-4-hydroxyphenylethanol and dopamine.