Synergistic effect of norepinephrine transporter blockade and α-2 antagonism on blood pressure in autonomic failure.

Patients with autonomic failure have disabling orthostatic hypotension because of impaired sympathetic activity. Norepinephrine transporter blockade with atomoxetine raises blood pressure in autonomic failure by increasing synaptic norepinephrine concentrations in postganglionic sympathetic neurons. This effect requires tonic release of norepinephrine, which is decreased in patients with low sympathetic tone. We hypothesized that increasing residual sympathetic outflow with the α-2 antagonist yohimbine would potentiate the pressor effect of norepinephrine transporter blockade with atomoxetine and improve orthostatic tolerance in peripheral autonomic failure. Seventeen patients received a single oral dose of either placebo, yohimbine 5.4 mg or atomoxetine 18.0 mg, and the combination yohimbine and atomoxetine in a single blind, crossover study. Blood pressure was assessed while patients were seated and standing for ≤10 minutes before and 1 hour postdrug. Neither yohimbine nor atomoxetine significantly increased seated systolic blood pressure or orthostatic tolerance compared with placebo. The combination, however, significantly increased seated systolic blood pressure and orthostatic tolerance (P<0.001 and P=0.016, respectively) in a synergistic manner. The maximal increase in seated systolic blood pressure seen with the combination was 31±33 mm Hg at 60 minutes postdrug. Only the combination showed a significant improvement in orthostatic symptoms. In conclusion, the combination of yohimbine and atomoxetine had a synergistic effect on blood pressure and orthostatic tolerance in peripheral autonomic failure, which may be explained by an increased release of norepinephrine in peripheral sympathetic neurons by α-2 antagonism combined with a reduced norepinephrine clearance by norepinephrine transporter blockade. Safety studies are required to address the clinical usefulness of this pharmacological approach.

ß-1 and ß-2 adrenergic receptor polymorphism and association with cardiovascular response to orthostatic screening.

Variation in the beta-1 and beta-2 adrenergic receptor genes (ADRB1 and ADRB2, respectively) may influence cardiovascular reactivity including orthostatic stress. We tested this hypothesis in a head-up tilt (HUT) screening protocol in healthy young adults without history of syncope. Following brachial arterial catheter insertion, 120 subjects (age 18-40, 72 females, Caucasian) underwent 5min 60° HUT. Polymorphisms tested were: Ser49/Gly and Arg389/Gly in ADRB1; and Arg16/Gly, Gln27/Glu, and Thr164/Ile in ADRB2. Three statistical models (recessive, dominant, additive) were evaluated using general linear models with analysis for each physiologic variable. A recessive model demonstrated a significant association between Arg16/Gly and: absolute supine and upright HR; HUT-induced change in cardiac index (CI), stroke index (SI) and systemic vascular resistance (SVR); and supine and upright norepinephrine values. Blood pressure was not influenced by genotype. Fewer associations were present for other polymorphisms: Ser49/Gly and the change in SI (dominant model), and Arg389/Gly and supine and HUT norepinephrine (additive model). We conclude that in this population, there is a robust association between Arg16/Gly and HUT responses, such that 2 copies of Arg16 increase supine and upright HR, and greater HUT-induced decreases in CI and SI, with greater increases in SVR and norepinephrine. ADRB1 gene variation appears to impact SI and plasma NE levels but not HR. Whether ADRB2 gene variation is ultimately disease-causing or disease-modifying, this study suggests an association between Arg16/Gly and postural hemodynamics, with sympathetic noradrenergic activity affected in a similar direction. This may have implications in the development of orthostatic disorders.

Excessive nitric oxide function and blood pressure regulation in patients with autonomic failure.

Approximately 50% of patients with autonomic failure (AF) suffer from supine hypertension, even those with very low plasma norepinephrine and renin. Because NO is arguably the most potent metabolic modulator of blood pressure, we hypothesized that impaired NO function contributes to supine hypertension in AF. However, we found that AF patients (n=14) were more sensitive to the pressor effects of the NO synthase inhibitor N(G)-monomethyl-l-arginine, suggesting increased NO function rather than deficiency; a lower dose of N(G)-monomethyl-l-arginine was needed to produce a similar increase in blood pressure in AF patients, as in healthy control subjects in whom AF was induced with the ganglionic blocker trimethaphan (171+/-37 mg versus 512+/-81 mg, respectively; P=0.001). Furthermore, potentiation of the actions of endogenous NO with the phosphodiesterase inhibitor sildenafil (25 mg PO) decreased nighttime supine systolic blood pressure from 182+/-11 to 138+/-4 mm Hg in 8 AF patients with supine hypertension (P=0.012 compared with placebo). Finally, AF patients tolerated a greater degree of upright tilt during infusion of N(G)-monomethyl-l-arginine (56+/-6 degrees versus 41+/-4 degrees with placebo; n=7; P=0.014), an improvement in orthostatic tolerance similar to that obtained with equipressor doses of phenylephrine. In conclusion, AF patients do not have NO deficiency contributing to supine hypertension. Instead, they have increased NO function contributing to their orthostatic hypotension. Potentiation of NO could be used in the treatment of supine hypertension, and its inhibition offers a novel approach to improve orthostatic hypotension.

Neuropharmacologic distinction of neurogenic orthostatic hypotension syndromes.

BACKGROUND: Neurogenic orthostatic hypotension (OH) characterizes pure autonomic failure (PAF), multiple system atrophy (MSA), and Parkinson disease (PD) with autonomic failure. We used neuropharmacologic probes that might distinguish these diseases based on loss of sympathetic noradrenergic nerves in PAF and PD + OH but not in MSA, and related the results to neurochemical and neuroimaging findings in the same patients. METHODS: Patients with neurogenic OH (PD + OH; N = 35), MSA (N = 41), and PAF (N = 12) received iv trimethaphan (TRI), which inhibits sympathetic nerve traffic, or yohimbine (YOH), which stimulates sympathetic traffic. Dependent measures included blood pressure, plasma norepinephrine (NE) levels, and interventricular septal myocardial radioactivity after iv injection of the sympathoneural imaging agent, 6-[F]fluorodopamine. RESULTS: The PD + OH and PAF groups had smaller pressor responses to YOH (12 +/- 8 and 13 +/- 1 mm Hg) and depressor responses to TRI (-14 +/- 8 and -17 +/- 7 mm Hg) than did the MSA group (43 +/- 8 mm Hg, -57 +/- 8 mm Hg; P = 0.01, P = 0.03). The PD + OH and MSA groups did not differ in NE responses to YOH and TRI. The depressor response to TRI, the pressor response to YOH, and the blood pressure difference between YOH and TRI all correlated positively with myocardial 6-[F]fluorodopamine-derived radioactivity. CONCLUSIONS: The PD + OH resembles PAF and differs from MSA in hemodynamic responses to drugs that alter NE release from sympathetic nerves. The results fit with sympathetic noradrenergic denervation in PD + OH and PAF but not in MSA.

New findings on the neuropathology of multiple system atrophy.

Multiple system atrophy (MSA) provides a typical example of the integrative role of the central autonomic network in controlling cardiovascular, respiratory, bladder and gastrointestinal functions. There is increasing evidence that neurochemically defined neuronal groups of the brainstem are selectively affected in MSA to a much greater degree than in Parkinson's disease. These include the catecholaminergic neurons of the rostral ventrolateral medulla (C1 group) which project to the intermediolateral cell column and are involved in modulation of sympathetic vasomotor outflow, and noradrenergic neurons of the caudal ventrolateral medulla (A1 group) projecting to the magnocellular nuclei of the hypothalamus and regulating vasopressin (AVP) release. Loss of these groups of neurons may, at least in part, explain the development of orthostatic hypotension, baroreflex dysfunction, and impaired reflex AVP release in response to hypotension. There is preliminary evidence that cardiovagal neurons of the ventrolateral portion of the nucleus ambiguus, distinct from the branchimotor neurons of the compact region, may also be affected in MSA. Loss of cholinergic neurons in the medullary arcuate nucleus, considered by some to be the homologous to the central chemosensitive region of the ventral medullary surface, may contribute to disturbances in automatic ventilation, particularly during sleep, in patients with MSA.

Cerebral blood flow and metabolism in multiple system atrophy of the Shy-Drager syndrome type: a PET study.

To investigate the role of the autonomic nervous system in cerebral blood flow (CBF) and metabolism, CBF and oxygen metabolism in patients with multiple system atrophy of the Shy-Drager syndrome type were examined. Seven patients with Shy-Drager syndrome were imaged using positron emission tomography and 15O-labeled gases. There was excellent local coupling between CBF and the cerebral metabolic rate of oxygen in the resting state. Elevation of blood pressure induced by leg raising increased CBF. The inhalation of CO2 also increased CBF in the Shy-Drager patients. These results showed that autoregulation is impaired in Shy-Drager syndrome, but local metabolic-flow coupling in the resting state and the CBF response to CO2 inhalation are spared. We conclude that the autonomic nervous system plays an important role in autoregulation, but not in local metabolic-flow coupling in the resting state. We suggest that metabolic mechanisms may mediate resting metabolic-flow coupling.

Glucose metabolism in the cortical and subcortical brain structures in multiple system atrophy and Parkinson's disease: a positron emission tomographic study.

The brain glucose metabolism was studied by PET with 18F-FDG in 11 patients with multiple system atrophy (MSA) and 12 patients with idiopathic Parkinson's disease (PD). Seven of the 11 MSA patients were diagnosed as having olivopontocerebellar atrophy, two had striatonigral degeneration, while two demonstrated Shy-Drager syndrome. The glucose metabolic rates for each region in the PD patients showed no difference from the normal controls. The frontal, temporal and parietal cortical glucose metabolic rates and the caudate, the putaminal, the cerebellar and the brainstem glucose metabolic rates in the MSA patients decreased significantly from the controls. The atrophy of the cerebellum and the brainstem in the MSA patients were scored by MRI. The cerebellar and brainstem glucose metabolism in the MSA patients decreased as the atrophy score in such regions advanced in each group; however, some patients with no atrophy showed a decreased glucose metabolism. Although the cerebellar and the brainstem glucose metabolism decreased in all MSA patients, such a decrease was not observed in the SND patients. The decrease in the glucose metabolism for the non-cortical regions in the MSA patients seems to be due to a diffuse depletion of the neurons not restricted to the nigrostriatal neurons. Deafferentation to the cerebral cortices seems to result in a decreased cortical metabolism. The differences in the glucose metabolism between MSA and PD as assessed by PET may be caused by the pathophysiological differences between MSA and PD, and such differences therefore appear to be useful when making a differential diagnosis between MSA and PD. The relative sparing of the brainstem and cerebellar glucose metabolism is considered to be a feature of patients with SND.

Benzodiazepine receptor binding in cerebellar degenerations studied with positron emission tomography.

We used positron emission tomography with [11C]flumazenil to study gamma-aminobutyric acid type A/benzodiazepine receptor binding quantitatively in the cerebral hemispheres, basal ganglia, thalamus, cerebellum, and brainstem of 72 subjects, including 14 with multiple system atrophy of the ataxic (olivopontocerebellar atrophy) type, 5 with multiple system atrophy of the extrapyramidal/autonomic (Shy-Drager syndrome) type, 18 with sporadic olivopontocerebellar atrophy, 15 with dominantly inherited olivopontocerebellar atrophy, and 20 normal control subjects with similar age and sex distributions. In comparison with data obtained from the normal control subjects, we found significantly decreased ligand influx in the cerebellum and brainstem of multiple system atrophy patients of the olivopontocerebellar atrophy type and in patients with sporadic olivopontocerebellar atrophy, but not in patients with multiple system atrophy of the Shy-Drager syndrome type. Despite these differences in ligand influx, benzodiazepine binding was largely preserved in the cerebral hemispheres, basal ganglia, thalamus, cerebellum, and brainstem in patients with multiple system atrophy of both types as well as those with sporadic or dominantly inherited olivopontocerebellar atrophy as compared with normal control subjects. The finding of relative preservation of benzodiazepine receptors indicates that these sites are available for pharmacological therapy in these disorders.

Decrease in cerebellin and corticotropin-releasing hormone in the cerebellum of olivopontocerebellar atrophy and Shy-Drager syndrome.

Four neuropeptides; cerebellin, corticotropin-releasing hormone (CRH), neuropeptide Y and somatostatin were studied by radioimmunoassay in the postmortem human brains obtained from three patients with olivopontocerebellar atrophy (OPCA) and one with Shy-Drager syndrome. Significant decreases in cerebellin and CRH concentrations were found in the cerebellar hemisphere of these diseases compared with controls. These findings suggest important pathophysiological roles of cerebellin and CRH in these cerebellar diseases. Such significant decreases were not found in neuropeptide Y and somatostatin.

Ubiquitinated alpha B-crystallin in glial cytoplasmic inclusions from the brain of a patient with multiple system atrophy.

Glial cytoplasmic inclusions (GCIs) have been observed in oligodendroglia-like cells, specifically in the brains of patients with multiple system atrophy (striatonigral degeneration, olivopontocerebellar atrophy and Shy-Drager syndrome). We have investigated GCIs from brains of patients with multiple system atrophy biochemically and immunochemically. While most GCIs have been reported positive for both ubiquitin and alpha B-crystallin in immunocytochemical studies, the components of GCIs have not been identified biochemically. GCI-bearing cells were partially purified from the OPCA brain by sieving with nylon meshes and discontinuous sucrose density gradient centrifugation. The fraction containing GCI-bearing cells was also found to contain a 32 kDa and a 40 kDa protein, both of which were specifically recognized by anti-ubiquitin and anti-alpha B-crystallin antibodies, neither of which was found in the same fraction derived from control brain. These immunochemical results suggest that ubiquitinated alpha B-crystallin is present in GCIs from the brains of patients with multiple system atrophy.

Cerebellar excitatory and inhibitory amino acid receptors in multiple system atrophy.

We studied excitatory and inhibitory amino acid binding sites autoradiographically in control and multiple system atrophy (MSA) cerebella. Within the dentate nucleus (DN) of MSA specimens, we found a significant increase in the level of GABAA, benzodiazepine, and metabotropic binding sites compared with controls. In the granule cell layer, kainate, N-methyl-D-aspartate, and GABAA binding sites were all decreased significantly in MSA specimens compared with controls. In the molecular layer of MSA cerebellum, alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate binding sites were decreased significantly compared with controls. Cerebellar cortical binding site decreases are likely due to Purkinje and granule cell loss. The increase of binding site levels in DN of MSA specimens may represent receptor up-regulation reflecting loss of descending inhibitory Purkinje cell and ascending excitatory afferents to the DN.

Shy-Drager syndrome with abnormal circadian rhythm of plasma antidiuretic hormone secretion and urinary excretion.

A 67-year-old patient with Shy-Drager syndrome (SDS), exhibited nocturnal polyuria associated with abnormal circadian rhythm of antidiuretic hormone (ADH) secretion and nocturnal polyuria. The patient excreted a larger volume of urine during the nighttime compared to that in the daytime. The specific gravity of urine at night was lower than that during the day. In contrast to normal circadian rhythm of ADH, the patient's plasma concentration of ADH was increased in the daytime. The present study raised the possibility that an altered circadian rhythm of plasma ADH secretion might be considered a result of the neurodegenerative changes involving the hypothalamus.

Immunohistochemical expression of microtubule-associated protein 5 (MAP5) in glial cells in multiple system atrophy.

An immunohistochemical study focusing on glial cells was performed using monoclonal antibodies against microtubule-associated proteins (MAP1, MAP2 and MAP5), transferrin, leukocyte common antigen (LCA) and glial fibrillary acidic protein (GFAP) in 5 cases of multiple system atrophy (MSA) exhibiting olivopontocerebellar atrophy and striatonigral degeneration. An antibody to MAP5, a fetal antigen in developing brain, was strongly demonstrated in the glial cytoplasmic inclusions (GCIs) which have recently drawn a great deal of attention and were observed in all 5 cases of MSA. Moreover, MAP5-positive glial cells (MAP5-Gs) were present in significantly higher number than in the controls in various regions where GCIs were found, predominantly in putamen, substantia nigra, cerebellar white matter and internal capsule. LCA and transferrin, markers of microglia and oligodendroglia, respectively, were immunohistochemically detected in some MAP5-Gs. GFAP, on the other hand, was not expressed in MAP5-Gs at all. These findings suggest that MAP5-Gs consist of reactive microglia and oligodendroglia. Our study is the first to demonstrate immunohistochemical detection of MAP5 in glial pathological changes in MSA.

[Dysautonomia and multi-systemic atrophy of the nervous system (Shy-Drager's syndrome)]. / Dysautonomie et atrophie multisystématisée du système nerveux (syndrome de Shy-Drager).

The clinical expressions of primary autonomic nervous system failure are more or less numerous, orthostatic hypotension being only one of them. Clinical analysis reveals 3 categories of manifestations: pure progressive dysautonomia, dysautonomia associated with Parkinson's disease, and dysautonomia associated with multiple system atrophy of the nervous system also known as Shy-Drager syndrome. Neuropathological studies show that lesions of the efferent autonomic nervous system (tractus intermediolateralis, sympathetic ganglia) are frequently associated with lesions of the central nervous system the role of which in dysautonomia is still imperfectly known. Lesions of the central nervous system may present as genuine Parkinson's disease with Lew bodies or as multiple systemic atrophy with its two best individualized aspects: striatonigral atrophy and olivopontocerebellar atrophy. These various neurological aspects have their counterpart in biochemical abnormalities, prognosis and response to treatment.

Positron emission tomography in Shy-Drager syndrome.

We studied the nigrostriatal dopaminergic pathway in 3 patients with Shy-Drager syndrome, by using positron emission tomography and [18F]6-fluoro-1-dopa to determine whether their parkinsonism correlated with impaired functional integrity of the presynaptic nigrostriatal pathway. One patient had short duration of disease, mild parkinsonism, and a normal positron emission tomographic scan, suggesting pathological changes functionally distal to the nigrostriatal pathway. Two patients with longer duration of disease had more severe parkinsonism and reduced [18F]6-fluoro-1-dopa uptake, suggesting impaired nigrostriatal dopaminergic function with progression of Shy-Drager syndrome.

A two-compartment description and kinetic procedure for measuring regional cerebral [11C]nomifensine uptake using positron emission tomography.

S-[11C]Nomifensine (S-[11C]NMF) is a positron-emitting tracer suitable for positron emission tomography, which binds to both dopaminergic and noradrenergic reuptake sites in the striatum and the thalamus. Modelling of the cerebral distribution of this drug has been hampered by the rapid appearance of glucuronide metabolites in the plasma, which do not cross the blood--brain barrier. To date, [11C]NMF uptake has simply been expressed as regional versus nonspecific cerebellar activity ratios. We have calculated a "free" NMF input curve from red cell activity curves, using the fact that the free drug rapidly equilibrates between red cells and plasma, while glucuronides do not enter red cells. With this free [11C]NMF input function, all regional cerebral uptake curves could be fitted to a conventional two-compartment model, defining tracer distribution in terms of [11C]NMF regional volume of distribution. Assuming that the cerebellar volume of distribution of [11C]NMF represents the nonspecific volume of distribution of the tracer in striatum and thalamus, we have calculated an equilibrium partition coefficient for [11C]NMF between freely exchanging specific and nonspecific compartments in these regions, representing its "binding potential" to dopaminergic or noradrenergic uptake sites (or complexes). This partition coefficient was lower in the striatum when the racemate rather than the active S-enantiomer of [11C]NMF was administered. In the striatum of patients suffering from Parkinson's disease and multiple-system atrophy, the specific compartmentation of S-[11C]NMF was significantly decreased compared with that of age-matched volunteers.

The effect of propranolol on catecholamine clearance.

Normal subjects given propranolol increased their plasma t1/2 for infused isoproterenol from 2.68 to 6.25 minutes. Propranolol increased plasma norepinephrine (NE) levels only slightly. Propranolol increased the t1/2 of isoproterenol but not that of NE in men with autonomic nervous system degeneration. This suggests that propranolol acts on nonneuronal uptake-2 processes, rather than on uptake-1 mechanisms. alpha-Blockers slow uptake-1 and beta-blockers slow uptake-2 processes. When 27 subjects exercised, those who attained the highest plasma levels of the alpha- and beta-receptor agonist NE also had the briefest apparent t1/2 for NE. Adrenergic receptor blocking drugs slow catecholamine clearance. NE may stimulate its own clearance.

Rapid clearance of iodine-131 MIBG from the heart and liver of patients with adrenergic dysfunction and pheochromocytoma.

Iodine-131 MIBG, a radiolabeled adrenergic neuron-blocking agent, decreased rapidly from the heart and liver of patients with adrenergic dysfunction (n = 3) and pheochromocytoma (n = 2) when compared with eight controls. The 4-hr activity expressed as percentages (mean +/- s.d.) of the 20-min counts were as follows: 80 +/- 3.0% in the controls compared with 60 +/- 7.6% in the patients over the heart (p less than 0.01) and 79 +/- 3.2% in the controls compared with 51 +/- 17% in the patients over the liver (p less than 0.02). However, there was no significant difference in the rate of [131I]MIBG decrease in these organs between controls and patients in the intervals subsequent to 4 hr (p greater than 0.05). These findings suggest that adrenergic neuronal uptake of [131I]MIBG in these organs is smaller in the patients than in the controls. Measurements of time-activity relationships of radioiodinated MIBG may be useful for assessment of adrenergic function of these organs and thus of generalized disorders of adrenergic innervation.