Afuni, a novel transforming growth factor-β gene is involved in arm regeneration by the brittle star Amphiura filiformis

The bone morphogenetic proteins (BMPs) are a family of the transforming growth factor-beta (TGF-beta) superfamily that perform multiple roles during vertebrate and invertebrate development. Here, we report the molecular cloning of a novel BMP from regenerating arms of the ophiuroid Amphiura filiformis. The theoretically translated amino acid sequence of this novel BMP has high similarity to that of the sea urchin BMP univin. This novel BMP has been named afuni. Whole-mount in situ hybridisation implicates afuni in arm regeneration. Expression occurs in distinct proximal and distal regions of late regenerates (3- and 5-week postablation). These sites are at different stages of regeneration, suggesting multiple roles for this gene in adult arm development. Cellular expression of this gene occurs in migratory cells within the radial water canal (RWC) of regenerating and nonregenerating arms. These migrating coelomocytes suggest a key role for the coelomic RWC as a source of the cellular material for use in arm regeneration by A. filiformis.

Biphasic, opposing modulation of cloned neuronal alpha1E Ca channels by distinct signaling pathways coupled to M2 muscarinic acetylcholine receptors

Neuronal alpha1E subunits are thought to form R-type Ca channels. When expressed in human embryonic kidney cells with M2 muscarinic acetylcholine receptors, Ca channels encoded by rabbit alpha1E exhibit striking biphasic modulation. Receptor activation first produces rapid inhibition of current amplitude and activation rate. However, in the continued presence of agonist, alpha1E currents subsequently increase. Kinetic slowing persists during this secondary stimulation phase. After receptor deactivation, kinetic slowing is quickly relieved, and current amplitude over-recovers before returning toward control levels. These features indicate that inhibition and stimulation of alpha1E are separate processes, with stimulation superimposed on inhibition. Pertussis toxin eliminates inhibition without affecting stimulation, demonstrating that inhibition and stimulation involve distinct signaling pathways. Neither inhibition nor stimulation is altered by coexpression of Ca channel beta2a or beta3 subunits. Stimulation is abolished by staurosporine and reduced by intracellular 5'-adenylylimidodiphosphate, suggesting that phosphorylation is required. However, stimulation does not seem to involve cAMP-dependent protein kinase, protein kinase C, cGMP-dependent protein kinase, tyrosine kinases, or phosphoinositide 3-kinases. Stimulation does not require a Ca signal, because it is not specifically altered by varying intracellular Ca buffering or by substituting Ba as the charge carrier. In contrast to those formed by alpha1E, Ca channels formed by alpha1A or alpha1B display only inhibition and no stimulation during prolonged activation of M2 receptors. The dual modulation of alpha1E may confer unique physiological properties on native R-type Ca channels. As one possibility, R-type channels may continue to mediate Ca influx during steady inhibition of N-type and P/Q-type channels by muscarinic or other receptors.

Short-term exposures of rats to airborne hydrogen fluoride

A series of acute inhalation exposures was performed with airborne hydrogen fluoride (HF) to establish the concentration response for nonlethal effects in the rat. Exposures were either 2 or 10 min long; concentrations ranged from 135 to 8621 ppm. Three additional exposures (20 to 48 ppm) were performed for 60 min. A mouth-breathing (MB) model with a tracheal cannula was used in most of the exposures to maximize delivery of the HF to the lower respiratory tract. Endpoints on the day after exposure included hematology, serum chemistry, bronchoalveolar lavage, pulmonary function, organ weights, and histopathology. Nasal resistance was measured in nose-breathing (NB) groups. Effects of exposure were generally limited to the respiratory tract and included alveolitis, bronchial lesions, altered parameters of pulmonary function and bronchoalveolar lavage, and mucosal necrosis, inflammation, and fibrinopurulent exudate in airways. Observed changes were concentration related and appeared more pronounced in major airways near the point of entry (trachea in MB animals and nose in NB animals). One group of MB animals exposed for 10 min to 1454 ppm was evaluated at 3 and 14 wk after exposure; the acute effects had resolved by those times. The effects of 2-min exposures were consistently more severe than those from 10-min exposures to the same product of concentration x time. Exposures of MB animals for 60 min to 20 or 48 ppm HF did not result in observable adverse effects, although quasistatic pressure-volume curves were shifted upward slightly after 48 ppm. These data provide an integrated picture of the concentration-related effects of short nonlethal exposures to HF.

Acute effects of 10-minute exposure to hydrogen fluoride in rats and derivation of a short-term exposure limit for humans

A series of acute inhalation exposures of female rats was conducted with hydrogen fluoride (HF) to establish a concentration-response curve for nonlethal exposures. Durations of 2 and 10 min were used to simulate possible short-term exposures. Concentrations of HF ranged from 593 to 8621 ppm for 2-min exposures and from 135 to 1764 ppm for 10-min exposures. Additional exposures were performed for 60 min at 20 and 48 ppm HF for comparison to existing Emergency Response Planning Guidelines. Animals were evaluated on the day after exposure for changes in parameters of bronchoalveolar lavage, pulmonary function, hematology, serum chemistry, body weight, organ weights, and histopathology. Most exposures were performed with orally cannulated animals to bypass absorption of HF in the nose and achieve maximum delivery of HF to the lower airways. One of the primary uses of the resulting data was to estimate a concentration to which most people could be exposed for 10 min without severe of irreversible health effects. This level was 130 ppm. It was predicted that irritation would occur at this concentration, but the effects on t he respiratory tract would not be "serious" and would be expected to be reversible. The results of this experiment and the subsequent analysis of the data provide an important aid in he planning of responses to an accidental release of HF.

Post-exertion dizziness as the sole presenting symptom of autonomic failure

An otherwise fit young man, leading an active life, whose only complaint at presentation was dizziness after extreme exertion is described. He was found later to have postural and exercise induced hypotension. Subsequently, he developed typical symptoms of autonomic failure, with postural dizziness, urinary abnormalities, and erectile failure. Progression of autonomic failure was documented on testing. A fall in blood pressure during or after exercise has been reported previously in pure autonomic failure, but a presentation with exercise induced symptoms alone is unusual.

Treatment of autonomic failure

The group of primary autonomic failure (AF) syndromes comprises pure AF (PAF), in which there are no central neurological signs, and multiple system atrophy (MSA) in which AF is accompanied by the overlapping degenerative disorders, striatonigral degeneration and olivopontocerebellar atrophy. Patients with these syndromes deteriorate progressively but, based on an understanding of the precise sites of the lesions, there are several ways of alleviating their deterioration, in particular the most disabling symptom, postural hypotension. The principles can be used in the treatment of AF in other general medical disorders, such as diabetes.

Striatal D2 receptor status in patients with Parkinson's disease, striatonigral degeneration, and progressive supranuclear palsy, measured with 11C-raclopride and positron emission tomography

Equilibrium striatal: cerebellar 11C-raclopride (RAC) uptake ratios reflect the density of striatal dopamine D2 binding sites. Using positron emission tomographic scanning we have measured striatal RAC uptake in 6 untreated patients with Parkinson's disease (PD), 5 chronically treated patients with PD and a fluctuating response to L-dopa, 10 patients with striatonigral degeneration (SND), and 9 patients with progressive supranuclear palsy (PSP). Regional cerebral blood flow was determined also, with C15O2. Mean striatal: cerebellar RAC uptake was not significantly different from normal in untreated patients with PD, though 2 of these 6 patients showed significantly increased putamen tracer binding. Mean caudate and putamen: cerebellar RAC uptake ratios of the group with PD and a fluctuating response to L-dopa were significantly reduced by 30% and 18%, respectively. The patients with SND had lesser, but significant, 10% and 11% decreases in mean caudate and putamen: cerebellar RAC uptake ratios, respectively, whereas patients with PSP showed 24% and 9% reductions in caudate and putamen: cerebellar RAC binding. Striatal and frontal blood flow were significantly reduced in patients with PSP, but not in patients with PD or SND. In conclusion, striatal D2 binding potential is normal or raised in untreated patients with PD, but reduced in patients with PD and a fluctuating response to L-dopa. Patients with SND and PSP show a decrease in striatal RAC binding, but to a lesser extent than patients with PD and a fluctuating response to treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of food on postural hypotension in three groups with chronic autonomic failure--clinical and therapeutic implications

The effect of a balanced liquid meal on supine and postural blood pressure (BP) responses was investigated in three groups of patients with chronic autonomic failure; 10 with associated neurological impairment (multiple system atrophy (MSA), Shy-Drager syndrome) and seven without (of which five had pure autonomic failure (PAF); and two had a deficiency of the enzyme dopamine beta hydroxylase, DBH-deficiency). All had marked postural hypotension. Subjects with normal autonomic function were also studied. In MSA and PAF food lowered supine BP substantially, with a more rapid and greater fall in PAF. After food, the levels of BP reached were considerably lower because of the reduced supine BP and many had to be returned to the horizontal position earlier than before. Ingestion of a similar volume of water alone had no effect in MSA or PAF. In DBH deficiency, food had variable but minimal effects on BP while supine and during head-up tilt. In subjects with normal autonomic function food did not affect BP. The BP responses to food thus varied in the three groups with chronic autonomic failure. The influence of food on both supine and postural BP therefore should be considered in the clinical and laboratory assessment of autonomic dysfunction and in relation to therapeutic approaches, designed to alleviate postural hypotension.

Differing patterns of striatal 18F-dopa uptake in Parkinson's disease, multiple system atrophy, and progressive supranuclear palsy

Using positron emission tomography (PET), we studied regional striatal 18F-dopa uptake in 16 patients with L-dopa-responsive Parkinson's disease (PD), 18 patients with multiple system atrophy, and 10 patients with progressive supranuclear palsy. Results were compared with those of 30 age-matched normal volunteers. The patients with PD showed significantly reduced mean uptake of 18F-dopa in the caudate and putamen compared to controls, but while function in the posterior part of the putamen was severely impaired (45% of normal), function in the anterior part of the putamen and in the caudate was relatively spared (62% and 84% of normal). Mean 18F-dopa uptake in the posterior putamen was depressed to similar levels in all patients. Unlike patients with PD, the patients with progressive supranuclear palsy showed equally severe impairment of mean 18F-dopa uptake in the anterior and posterior putamen. Caudate 18F-dopa uptake was also significantly lower in patients with progressive supranuclear palsy than in patients with PD, being depressed to the same level as that in the putamen. Mean 18F-dopa uptake values in the anterior putamen and caudate in patients with multiple system atrophy lay between PD and progressive supranuclear palsy levels. Locomotor disability of individual patients with PD or multiple system atrophy correlated with decline in striatal 18F-dopa uptake, but this was not the case for the patients with progressive supranuclear palsy. We conclude that patients with PD have selective nigral pathological features with relative preservation of the dopaminergic function in the anterior putamen and caudate, whereas there is progressively more extensive nigral involvement in multiple system atrophy and progressive supranuclear palsy.(ABSTRACT TRUNCATED AT 250 WORDS)

The relationship between locomotor disability, autonomic dysfunction, and the integrity of the striatal dopaminergic system in patients with multiple system atrophy, pure autonomic failure, and Parkinson's disease, studied with PET

18F-dopa and S-11C-nomifensine (NMF) are positron emitting tracers whose caudate and putamen uptake reflects striatal dopamine storage capacity and the integrity of dopamine reuptake sites, respectively. Using these two tracers, the integrity of the presynaptic striatal dopaminergic system has been studied with positron emission tomography (PET) in 10 subjects with multiple system atrophy (MSA, Shy-Drager syndrome) who had an akinetic-rigid syndrome that was poorly responsive to L-dopa, autonomic failure, and cerebellar ataxia. PET findings for the 10 MSA patients were compared with those for 13 age-matched controls, 8 subjects with L-dopa responsive Parkinson's disease (PD), and 7 subjects with pure autonomic failure (PAF). Influx constants, Ki, reflecting specific 18F-dopa uptake into striatal tissue, were severely reduced in the putamen and caudate of the 10 MSA subjects (mean putamen Ki 0.005 min-1 MSA vs 0.013 min-1 controls; mean caudate Ki 0.007 min-1 MSA vs 0.013 min-1 controls). Reduction of putamen, but not caudate, 18F-dopa uptake correlated with severity and duration of locomotor disability. Eight patients with PD, and a similar degree and duration of locomotor disability to the patients with MSA, demonstrated equal impairment of mean putamen 18F-dopa uptake, but significant preservation of mean caudate function. The 7 PAF patients had normal mean levels of putamen and caudate 18F-dopa uptake, although 1 individual PAF patient had significantly impaired striatal function. The MSA and PD groups of subjects both showed significantly reduced levels of specific striatal S-11C-NMF binding, again caudate function being relatively preserved in PD. It is concluded that in both MSA and PD there is a parallel decline of striatal dopamine storage capacity and reuptake site integrity, probably reflecting a loss of nigrostriatal nerve terminals. Caudate function is relatively preserved in PD compared with MSA. The majority of PAF patients have an intact nigrostriatal dopaminergic system, suggesting that PAF is a condition distinct from PD and MSA in spite of some pathological similarities. PET is capable of detecting subclinical nigrostriatal involvement in PAF patients when this is present.

The neurological complications of Anderson-Fabry disease (alpha-galactosidase A deficiency)--investigation of symptomatic and presymptomatic patients

Anderson-Fabry disease is an X-linked inborn error of metabolism characterized by subnormal activity of the lysosomal hydrolase, alpha-galactosidase A. We have assessed the incidence and nature of neuropathy in 12 patients (seven affected men and five carrier females). Abnormalities of cutaneous thermal sensation were common, even in asymptomatic carriers, with a unique predilection for cold sensitivity which suggests involvement of small myelinated nerve fibres. Intracranial abnormalities were frequently detected by magnetic resonance imaging (MRI) in males, both with and without overt cerebrovascular disease, and were more extensive in older patients. Such abnormalities were not detected in carriers. Auditory and vestibular abnormalities were present in six patients, only one of whom was symptomatic. Cranial MRI and assessment of cutaneous thermal thresholds are sensitive techniques which can identify neurological involvement in asymptomatic patients. They may be of benefit in monitoring the effectiveness of enzyme replacement therapy and excluding the carrier state for the defective gene.

Abnormal respiration and sudden death during sleep in multiple system atrophy with autonomic failure

We studied respiration during sleep in 7 patients with multiple system atrophy and autonomic failure (MSA-AF) and 7 control subjects. Although mean respiratory rate, tidal volume, and inspiratory flow rate were statistically similar in both groups, the coefficients of variability in all were significantly greater in MSA-AF patients. Four of 5 nontracheostomized had evidence of upper airway obstruction without significant oxygen desaturation. Three of these 5 patients died suddenly during sleep. MSA-AF is associated with upper airway dysfunction and disordered central respirations which can be life threatening. Evidence of even mild obstruction during sleep should warrant tracheostomy.

Prevention of glucose-induced hypotension by the somatostatin analogue octreotide (SMS 201-995) in chronic autonomic failure: haemodynamic and hormonal changes

1. The haemodynamic and hormonal changes following glucose ingestion (1 g/kg) were determined before and after pretreatment with either placebo or the somatostatin analogue, octreotide (SMS 201-995, 50 micrograms subcutaneously), in seven patients with chronic autonomic failure. 2. In the placebo phase, after glucose, there was a marked and prolonged fall in blood pressure with no change in cardiac index and peripheral blood flow. Plasma insulin and neurotensin levels increased, whereas glucagon, vasoactive intestinal polypeptide, noradrenaline and adrenaline levels were unchanged. 3. Octreotide transiently raised blood pressure and prevented glucose-induced hypotension. There were no changes in cardiac index or peripheral blood flow. Plasma insulin and neurotensin levels did not rise. Plasma glucose levels increased more slowly but reached a similar level to the placebo phase. 4. We conclude that in autonomic failure patients, glucose-induced hypotension was not accompanied by changes in cardiac index or peripheral blood flow, indicating a lack of compensation to probable splanchnic vasodilatation. The hypotension was prevented by the peptide release inhibitor, octreotide, with no change in cardiac index or in peripheral blood flow, suggesting an effect on the splanchnic vasculature, probably through inhibiting release of vasodilatatory pancreatic and gut peptides.

Angiotensin converting enzyme inhibition lowers blood pressure in patients with primary autonomic failure independently of plasma renin levels and sympathetic nervous activity

The haemodynamic and neurohormonal responses to the angiotensin converting enzyme (ACE) inhibitor captopril were studied in 12 patients with primary autonomic failure; seven had multiple system atrophy and five had pure autonomic failure. Basal supine mean arterial blood pressure was higher in the patients with multiple system atrophy than in those with pure autonomic failure and the normal subjects. Basal plasma noradrenaline levels were normal in the patients with multiple system atrophy, but lower in those with pure autonomic failure. Captopril lowered the mean arterial pressure in the patients with multiple system atrophy and pure autonomic failure but not in the normal subjects. In the patients with multiple system atrophy and pure autonomic failure, captopril lowered the cardiac output and the stroke volume. Forearm vascular resistance was unchanged. No significant changes occurred in the normal subjects. Plasma renin activity was unchanged after captopril in the patients with autonomic failure, but rose in the normal subjects. Plasma noradrenaline was unchanged in all groups after the administration of captopril. We conclude that captopril lowers the mean arterial pressure in patients with multiple system atrophy and pure autonomic failure. After the administration of captopril there is a reduction in cardiac output, secondary to a fall in stroke volume. The vasodepressor response to captopril in patients with autonomic failure is not related to the basal level of plasma renin activity or sympathetic nervous activity, indicating that the hypotensive effects of bradykinin or prostaglandins, or both, may contribute.

Relationship between splanchnic vasodilation and postprandial hypotension in patients with primary autonomic failure

The haemodynamic responses to a standard liquid meal were measured in patients with autonomic failure and in normal subjects. Resting superior mesenteric artery blood flow was similar in both groups, but mean supine arterial pressure and the superior mesenteric artery vascular resistance were higher in the patients with autonomic failure than in the normal subjects. After the meal there was a rise in superior mesenteric artery blood flow and a fall in superior mesenteric artery vascular resistance in both groups. Mean arterial blood pressure fell substantially after food in the patients with autonomic failure but not in the normal subjects. The basal heart rate, stroke distance and cardiac index were higher in the patients with autonomic failure, and rose significantly after the meal only in the normal subjects. Forearm blood flow fell and the vascular resistance rose after the meal in the normal subjects but not in the patients with autonomic failure. We conclude that superior mesenteric artery blood flow rose and superior mesenteric artery vascular resistance fell after the meal in the normal subjects and in the patients with autonomic failure. However, in the normal subjects the blood pressure was maintained by factors which include a rise in the heart rate and cardiac output. The lack of such compensatory changes probably accounts for postprandial hypotension in patients with autonomic failure.

Cardiovascular, biochemical and hormonal changes during food-induced hypotension in chronic autonomic failure

The cardiovascular, biochemical and hormonal responses to a standard test meal have been investigated in patients with chronic autonomic failure and normal subjects. In autonomic failure there was a rapid (within 15 min), substantial and prolonged fall in blood pressure after the meal. A marked fall in blood pressure also occurred after a liquid meal of similar composition and caloric content, with no change in blood pressure in age-matched subjects with normal autonomic function. In autonomic failure after the test meal the blood pressure reached its nadir (45% fall) after 60 min, and had not returned to pre-meal levels after 3 h. There were no changes in cutaneous and forearm blood flow. In the normal subjects there were no changes in blood pressure after the meal; forearm blood flow fell and cardiac output increased. In autonomic failure there were no changes in plasma noradrenaline levels, unlike the normal subjects. Plasma adrenaline levels were unchanged in both groups. There was a similar rise in levels of plasma renin activity in both groups. The haematocrit and plasma osmolality did not change in either group. Changes in plasma glucose and plasma insulin levels were similar in both groups. The responses of 3 pancreatic gut peptides, neurotensin, pancreatic polypeptide and enteroglucagon, were greater in autonomic failure. Basal levels and responses of vasoactive intestinal polypeptide, cholecystokinin-8 and somatostatin were similar in both groups. The motilin response was greater in normal subjects. We conclude that in patients with autonomic failure there was a rapid, substantial and prolonged fall in blood pressure after a meal. This reduction in blood pressure was not counteracted by an increase in sympathetic nervous activity and other compensatory changes, as occur normally. It was unlikely that osmotic effects of the meal or gut secretions resulted in a significant loss of intravascular fluid into the gut. The fall in blood pressure probably results from vasodilatation within the splanchnic circulation, to which pancreatic and gastrointestinal hormones with vasodilatory actions may contribute.

The value of urethral sphincter electromyography in the differential diagnosis of parkinsonism

A series of 54 patients presenting with parkinsonism underwent clinical assessment and urethral sphincter electromyography (EMG). After clinical assessment, 26 were thought to be suffering from probable multiple system atrophy (MSA), 15 were thought to have possible MSA and 13 were diagnosed as having probable idiopathic Parkinson's disease (IPD). Of those with probable MSA, 16 were found to have an abnormal urethral sphincter EMG. In the group with possible MSA, only 5 patients had an abnormal EMG while in the group with probable IPD, only 1 patient had an abnormal EMG. It was concluded that urethral sphincter electromyography provides a useful method of distinguishing between idiopathic Parkinson's disease and multiple system atrophy. It also provides a means of identifying those patients with parkinsonism whose incontinence may well be worsened, or in whom incontinence may develop following lower urinary tract surgery.

The effect of orthostatic hypotension on cerebral blood flow and middle cerebral artery velocity in autonomic failure, with observations on the action of ephedrine

Cerebral blood flow (CBF) and middle cerebral artery velocity (MCAv) have been measured using 133xenon washout and transcranial Doppler in ten patients with autonomic failure. Four pure autonomic failure and four multiple system atrophy patients behaved similarly: tilting them sufficiently to induce significant orthostatic hypotension without causing syncopal symptoms led to a significant fall in their mean MCAv, but no change in their mean CBF. These findings suggest that cerebral autoregulation is preserved in autonomic failure, orthostatic hypotension resulting in a reactive vasodilatation which lowers MCAv, reduces vascular resistance, and maintains CBF. Ephedrine helped to correct the orthostatic hypotension, but had no direct effect on CBF. Two siblings with orthostatic hypotension secondary to dopamine-beta-hydroxylase deficiency also had preserved cerebral autoregulation, but ephedrine led to paradoxical hypotension in these patients.

Differential blood pressure and hormonal effects after glucose and xylose ingestion in chronic autonomic failure

1. To investigate whether carbohydrate contributes to postprandial hypotension in autonomic failure, the cardiovascular, biochemical and hormonal effects of oral glucose and an iso-osmotic solution of oral xylose were studied on separate occasions in six patients with chronic autonomic failure. The effects of oral glucose were also studied in eight normal subjects. 2. In the patients oral glucose lowered blood pressure substantially (-34 +/- 7% at 60 min, area under curve -24.9 +/- 3.5%, P less than 0.001) and for a prolonged period (-25 +/- 4% at 120 min). Plasma noradrenaline levels did not change. In the normal subjects blood pressure was unchanged and plasma noradrenaline rose, suggesting a compensatory increase in sympathetic nervous activity. 3. In the patients xylose caused a smaller and more transient fall in blood pressure (-15 +/- 6% at 90 min, area under curve -8.9 +/- 4%, P less than 0.05) with a non-significant elevation in packed cell volume (36.7 +/- 1.8 to 38.2 +/- 1.8). It was therefore unclear if xylose was exerting osmotic effects within the bowel which contributed to the small blood pressure fall. Packed cell volume did not change in either the patients or normal subjects after glucose. 4. In the patients and normal subjects plasma insulin rose after glucose. Insulin levels were unchanged after xylose. Levels of pancreatic polypeptide and neurotensin, a potential vasodilator, rose in the patients only. The latter rose to a similar extent after both glucose and xylose, making it unlikely that neurotensin alone accounted for the hypotension. 5. These studies indicate that the carbohydrate components of a meal, and in particular those causing insulin release, contribute to postprandial hypotension in patients with autonomic failure.

Selective defect in gonadotrophin secretion in patients with autonomic failure

We studied the neuroendocrine effects of a condition associated with abnormal hypothalamic amines. Hypothalamo-anterior pituitary function was assessed in five male subjects with autonomic failure (AF) and in five age and sex-matched controls. All subjects showed normal gonadotrophin and TSH responses to GnRH and TRH, respectively. In control subjects, intravenous infusion of naloxone caused a significant rise in overall LH concentrations as well as increased frequency and amplitude of LH pulses. In contrast, in AF subjects naloxone did not alter LH concentrations or increase LH pulse frequency. Naloxone also caused an increase in neurosecretory GH pulses not only in AF subjects but also in the controls. These results suggest that in man, ascending catecholamine pathways are important in the control of gonadotrophin secretion. The markedly different response of GH to an opioid antagonist in elderly subjects should be further investigated.

6-Methyl-1,3,8-trichlorodibenzofuran (MCDF) as a 2,3,7,8-tetrachlorodibenzo-p-dioxin antagonist in C57BL/6 mice

6-Methyl-1,3,8-trichlorodibenzofuran (MCDF), 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and TCDD plus MCDF were administered to C57BL/6 mice and their effects on several aryl hydrocarbon (Ah) receptor-mediated responses including hepatic microsomal aryl hydrocarbon hydroxylase (AHH) and ethoxyresorufin O-deethylase (EROD) induction, immunotoxicity and teratogenicity were determined. MCDF did not induce hepatic microsomal AHH and EROD at doses up to 500 mumol/kg, however, co-administration of MCDF (50 mumol/kg) with a dose of TCDD which elicited a submaximal induction response (i.e. ED80-100, 15 nmol/kg) resulted in some small but significant inhibition of the induction of hepatic microsomal AHH and EROD (14 and 17%, respectively) compared to that observed with TCDD alone. Co-administration of TCDD and other doses of MCDF (10, 100, 200 or 500 mumol/kg) did not effect the induction response. These results were in contrast to the effectiveness of MCDF as an antagonist of the induction of AHH and EROD by TCDD in the rat (up to 50% inhibition of monooxygenase induction). Administration of MCDF (4, 20 and 40 mumol/kg) to C57BL/6 mice caused some inhibition of the splenic plaque-forming cell response to sheep erythrocytes only at the highest dose (26% decrease); the interaction of MCDF (4, 20 and 40 mumol/kg) and an immunotoxic dose of TCDD (3.7 nmol/kg) resulted in significant protection from the immunotoxic effects of TCDD at the 2 higher dose levels of MCDF. Similarly, MCDF (400 mumol/kg) did not cause cleft palate in mice but at this dose level MCDF afforded some protection from TCDD (20 micrograms/kg)-mediated cleft palate in mice. However, studies utilizing [3H]TCDD suggested that the protective effects may be due to modulation of TCDD reaching the palate in the co-treated animals (MCDF plus TCDD). Although both MCDF and Aroclor 1254 were both weak Ah receptor agonists in C57BL/6 mice, the former compound was much less effective as a TCDD antagonist. The observed species-specific effects for these 2 TCDD antagonists may be related species-dependent differences in receptor structure and receptor-ligand (i.e. agonist or antagonist) interactions.

Marked depletion of dorsal spinal cord substance P and calcitonin gene-related peptide with intact skin flare responses in multiple system atrophy

In view of the presence of neuropeptides in spinal cord autonomic pathways, their regional concentration was studied in post mortem thoracic cord from four cases of multiple system atrophy with progressive autonomic failure (MSA). A marked depletion was observed of substance P, its related peptide substance K, and of calcitonin gene-related peptide (CGRP), particularly in dorsal regions where peptide-containing sensory fibres terminate. As substance P and CGRP in primary sensory fibres are considered mediators of skin flares in Lewis' triple response, histamine-induced skin flares were measured in 12 MSA patients and were found to be preserved. These results provide a new key to the classification and aetiology of autonomic and multiple system degenerations, as well as a model to study the role of sensory neuropeptides in man.

Aroclor 1254 as a 2,3,7,8-tetrachlorodibenzo-p-dioxin antagonist: effects on enzyme induction and immunotoxicity

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and Aroclor 1254 induced the cytochrome P-450 dependent monooxygenases, aryl hydrocarbon hydroxylase (AHH) and ethoxyresorufin O-deethylase (EROD) in rat hepatoma H-4-II E cells and C57BL/6J mice. It has been proposed that both Aroclor 1254 and 2,3,7,8-TCDD induce these enzymes via a common mechanism which features initial binding to the aryl hydrocarbon (Ah) cytosolic receptor protein. The major difference between these compounds was the relative potency (i.e. 2,3,7,8-TCDD much greater than Aroclor 1254). Cotreatment of rat hepatoma H-4-II E cells or C57BL/6J mice with a dose of 2,3,7,8-TCDD which submaximally induces AHH and EROD and a dose of Aroclor 1254 which exhibited little or no induction activity resulted in significant antagonism of the induction effects of 2,3,7,8-TCDD. For example, cotreatment of C57BL/6J mice with 2,3,7,8-TCDD (15 nmol/kg) and Aroclor 1254 (25, 75 and 150 mumol/kg) resulted in up to 23% antagonism of AHH induction by 2,3,7,8-TCDD. Moreover, cotreatment with a higher dose of the 2,3,7,8-TCDD agonist (30 or 50 nmol/kg) partially reversed some of the antagonism by Aroclor 1254. In vivo antagonism was observed only at Aroclor 1254/2,3,7,8-TCDD molar ratios of 1667:1, 5000:1 and 10,000:1. Administration of 2,3,7,8-TCDD (3.72 nmol/kg) to C57BL/6J mice resulted in a 76% decrease in the splenic plaque forming cell response to sheep red blood cells. This T-cell mediated immunotoxic effect of 2,3,7,8-TCDD segregates with the Ah locus. In contrast, administration of 5, 15, 75 and 150 mumol/kg of Aroclor 1254 resulted in impairment of the immune response only at the highest dose level. However, cotreatment of mice with 2,3,7,8-TCDD (3.72 nmol/kg) and Aroclor 1254 (5, 15 or 75 mumol/kg) resulted in no significant decrease in the plaque forming cell response and complete protection from the immunotoxicity of 2,3,7,8-TCDD. Cotreatment of the mice with Aroclor 1254 (75 mumol/kg) and a higher dose of the 2,3,7,8-TCDD agonist resulted in partial reversal of the protective effects of Aroclor 1254. The in vitro and in vivo data suggest that within specific antagonist/agonist dose ratios, Aroclor 1254 can antagonize at least 2 Ah receptor-mediated effects of 2,3,7,8-TCDD, namely AHH induction and immunotoxicity.

Hypotensive and sedative effects of insulin in autonomic failure

The haemodynamic responses to intravenous insulin (0.15 units/kg) were measured in five patients with chronic autonomic failure who were not receiving drug treatment. After the administration of insulin supine blood pressure fell steadily, with a substantial reduction even before the onset of hypoglycaemia. None of the patients showed the usual range of neuroglycopenic symptoms, but they all became drowsy, with increasing sedation as the blood glucose concentration fell. In four other patients with autonomic dysfunction intravenous injection of 25-50 ml of 50% glucose alone caused a striking, although transient, fall in blood pressure. Hypoglycaemia was reversed by a 10 minute intravenous infusion of 100 ml of 25% glucose; this did not lower blood pressure further and rapidly restored previous levels of alertness. Consideration must be given to the hypotensive potential of insulin in patients with autonomic failure during an insulin stress test. The inability of these patients to show the usual manifestations of hypoglycaemia, plus the short lived, though pronounced, reduction in blood pressure after intravenous administration of 50% glucose, may further increase the risks of this procedure.

Synergistic interactions of 2,3,7,8-TCDD and 2,2',4,4',5,5'-hexachlorobiphenyl in C57BL/6J and DBA/2J mice: role of the Ah receptor

Treatment of C57BL/6J mice with 2,2',4,4',5,5'-hexachlorobiphenyl (HCBP, 500 mumol/kg) elevated hepatic cytosolic Ah receptor levels 82-107% for up to 14 days. Scatchard analysis of the [3H]2,3,7,8-TCDD (TCDD)-Ah receptor saturation binding curves from corn oil and HCBP treated rats gave KD values of 0.80 and 0.90 nM, respectively and confirmed that treatment with HCBP did not significantly alter receptor-radioligand affinities. Administration of HCBP to DBA/2J mice did not result in detectable hepatic cytosolic Ah receptor levels. Cotreatment of C57BL/6J mice with HCBP (500 mumol/kg) at a dose level of TCDD (1 nmol/kg) which elicited less than 10% of the maximum induction response resulted in significant synergistic induction of hepatic EROD and AHH [compared to animals treated only with TCDD (1 nmol/kg)]. In contrast, cotreatment of C57BL/6J mice with HCBP (500 mumol/kg) and maximally inducing dose levels of TCDD (100 or 500 nmol/kg) resulted in either a slight or no difference in the induction of AHH or EROD compared to the induction responses observed in mice treated only with TCDD. In contrast, cotreatment of DBA/2J mice with TCDD and HCBP (500 mumol/kg) resulted in significant synergistic induction of AHH and EROD at both submaximal (10-500 nmol/kg) and maximal (5000 nmol/kg) induction levels of TCDD. The only significant interactive effect of HCBP (500 mumol/kg) on the toxicity of TCDD in C57BL/6J and DBA/2J was protection from body weight loss observed after cotreatment of HCBP and TCDD in DBA/2J mice.

The effect of desmopressin on nocturnal polyuria, overnight weight loss, and morning postural hypotension in patients with autonomic failure

Day and night urine volume, morning and evening body weight, and supine and sitting blood pressure were measured in five patients with chronic autonomic failure who were not receiving treatment with drugs. All had nocturnal polyuria, overnight weight loss, and a pronounced postural fall in blood pressure, with lowest levels in the morning. Desmopressin (2-4 micrograms given intramuscularly at 8 pm) reduced nocturnal polyuria, diminished overnight weight loss, raised supine blood pressure, and reduced the postural fall, especially in the morning, when patients were often at their worst. Desmopressin may be a useful alternative to, or may supplement, other forms of treatment in some patients with autonomic failure.

Pressor effect of arginine vasopressin in progressive autonomic failure

The blood pressure (BP) and heart rate (HR) responses to 5 min incremental intravenous infusions of noradrenaline (NA) and arginine vasopressin (AVP) were investigated both in patients with progressive autonomic failure (PAF) and in normal volunteers. Stepwise infusion of NA at rates of 300-3000 pmol min-1 kg-1 produced a bradycardia and a dose related increase in BP in normal subjects. In subjects with PAF there was no significant HR response but the dose-BP response was shifted to the left with significant pressor responses at infusion rates of 60-300 pmol min-1 kg-1. Stepwise infusion of AVP at 0.2-5.0 pmol min-1 kg-1 caused transient bradycardia but no pressor response in seven normal volunteers. Further increases in AVP infusion in three other subjects achieved plasma AVP levels as high as 3000-4000 pmol/l, and still no significant pressor response was observed. Stepwise infusion of AVP at 0.05-2.0 pmol min-1 kg-1 in the eight subjects with PAF resulted in a pressor response without any change in HR. During this infusion plasma AVP increased from 0.8 +/- 0.2 (mean +/- SEM) to 30 +/- 2 pmol/l. A significant pressor response was already apparent at a plasma AVP level of 5.5 +/- 1.8 pmol/l.

Urethro-vesical dysfunction in progressive autonomic failure with multiple system atrophy

Fourteen patients with progressive autonomic failure and multiple system atrophy have been investigated by urodynamic, electromyographic and neurohistochemical means and the results compared with a series of age-matched controls. Three fundamental abnormalities of lower urinary tract function have been identified: (1) Involuntary detrusor contractions in response to bladder filling. It is suggested that these may be the result of a loss of inhibitory influences from the corpus striatum and substantia nigra. (2) Loss of the ability to initiate a voluntary micturition reflex. This may reflect the degeneration of neurons in pontine and medullary nuclei and in the sacral intermediolateral columns. In addition, these studies have demonstrated a significant reduction in the density of acetylcholinesterase-containing nerves in bladder muscle. (3) Profound urethral dysfunction. This appears to be partly due to a loss of proximal urethral sphincter tone, which causes bladder neck incompetence. In addition, the function of the striated component of the urethral sphincter is impaired. Individual motor units recorded from this muscle were clearly abnormal when compared with controls and suggested that reinnervation had occurred. We suggest that this is the result of degeneration of a specific group of sacral anterior horn cells known as Onuf's nucleus. The evidence that these particular motor units are affected, while others are spared, poses fundamental questions about the nature of selective vulnerability in degenerative diseases of the nervous system.

Atrial demand pacing to protect against vagal overactivity in sympathetic autonomic neuropathy

The clinical features, investigation and management of a patient with a subacute autonomic neuropathy are described. A series of physiological and biochemical studies indicated severe but selective sympathetic cardiovascular dysfunction, associated with bradycardia. The bradycardia was enhanced by raising blood pressure but there was no other evidence either of cardiac vagal impairment or hyperreactivity. Oral atropine prevented the bradycardia but had to be withdrawn because of intolerable side effects. An atrial demand pacemaker was implanted to elevate basal heart rate and prevent bradycardia. The pacemaker alone did not improve postural hypotension but it enabled the blood pressure to be readily and safely controlled by a combination of drugs.

Brain stem auditory evoked potentials in patients with multiple system atrophy with progressive autonomic failure (Shy-Drager syndrome)

Brain stem potentials from three groups of patients, namely those with pure progressive autonomic failure, Parkinson's disease and multisystem atrophy with progressive autonomic failure (Shy-Drager syndrome) were compared with each other and a group of normal subjects. In virtually all the patients with multisystem atrophy with progressive autonomic failure the brain stem potentials were abnormal in contrast to normal findings with Parkinson's disease. The closely associated group of patients with progressive autonomic failure alone also revealed no abnormalities of the BAEP. This separation of the two groups, Parkinson's disease and progressive autonomic failure from multisystem atrophy with progressive autonomic failure is important clinically as multiple system atrophy of the Shy-Drager type has extra-pyramidal features closely resembling Parkinsonism or a late onset cerebellar degeneration. From the abnormalities of the brain stem response in multisystem atrophy with progressive autonomic failure, it is clear that some disruption of the auditory pathway occurs in the ponto-medullary region as in nearly all patients there is a significant delay or reduction in the amplitude of components of the response generated beyond this region. The most likely area involved is the superior olivary complex.

Unmasking of the cardiovascular effects of carbohydrate in subjects with sympathetic denervation

The cardiovascular, biochemical and hormonal effects of a standard meal and two differing carbohydrates have been studied in normal subjects and in patients with autonomic failure (AF) and impaired cardiovascular reflexes. In the normal subjects blood pressure (BP) was unchanged after a meal and oral glucose. In AF patients, however, there was a marked and prolonged fall in BP after the meal. A similar fall occurred after oral glucose with only a small fall after oral xylose. In normal subjects, the meal and glucose raised plasma noradrenaline levels, unlike in AF patients, in whom noradrenaline and adrenaline levels were unchanged. In normal subjects with intact autonomic reflexes there are minimal cardiovascular effects induced by a meal or glucose. In AF subjects neural mechanisms are impaired, which probably unmasks the primary effects of food ingestion. The ability of glucose, but not xylose, to induce a similar degree of hypotension suggests that insulin may play an important role in postcibal hypotension.

Bladder dysfunction in distal autonomic neuropathy of acute onset

A patient with cholinergic dysautonomia and a patient with pandysautonomia have each been investigated for disturbances of bladder and urethral function. Both patients suffered from an inability to develop or sustain a detrusor contraction, while retaining normal bladder sensation. Biopsy specimens of bladder muscle stained for acetylcholinesterase revealed a significant reduction in cholinergic nerves compared with controls; however, the prominent cholinergic subepithelial plexus was strikingly preserved. These findings lend support to the view that acetylcholinesterase-containing nerves in the bladder muscle are motor fibres responsible for detrusor contraction, while those located in the subepithelium are sensory in function. Urethral sphincter electromyography revealed no abnormality of individual motor units, confirming that motor unit integrity in this muscle is dependent upon somatic rather than autonomic innervation. In the patient with pandysautonomia the proximal urethra was incompetent, while in the patient with cholinergic dysautonomia the bladder neck remained closed, as in controls. This suggests that sympathetic rather than parasympathetic efferent activity is necessary for the maintenance of proximal urethral competence.

Vasopressin secretion in progressive autonomic failure: evidence for defective afferent cardiovascular pathways

Patients with progressive autonomic failure with multiple system atrophy show a severely blunted response of plasma arginine vasopressin to the stimulus of head-up tilt. Whether this could be due to lesions either at one or more sites within ascending neural pathways from cardiovascular stretch receptors in the thorax or, alternatively, to lesions affecting vasopressin secreting cells within the hypothalamus was investigated. The arginine vasopressin response to an intravenous infusion of hypertonic saline was determined in six patients with progressive autonomic failure. The mean plasma concentration of arginine vasopressin rose from 1.0 to 3.7 pmol/l, a change comparable to that observed in normal controls. This demonstrates normal functioning of the efferent connections from the osmoreceptors within the hypothalamus and suggests that the loss of vasopressin response to head-up tilt is due to lesions in ascending pathways from cardiovascular receptors. There was a significant rise in mean blood pressure during the infusions on patients with progressive autonomic failure, a change which was not observed with the controls. This may have been at least partly caused by the rise in circulating arginine vasopressin concentrations, since these patients have been reported to be extremely sensitive to the pressor effects of arginine vasopressin.

Plasma volume regulation in patients with progressive autonomic failure during changes in salt intake or posture

Blood pressure in patients with progressive autonomic failure falls during salt restriction or orthostasis. We contrasted the regulation of plasma volume in patients with progressive autonomic failure with that of controls to determine whether hypovolemia contributes to this hypotension. When sitting, the plasma volume (measured from distribution of human serum albumin) was normal. During 1 week of low Na+ intake, patients with progressive autonomic failure lost three times as much body weight as controls; however, changes in plasma volume were strictly comparable. Therefore, the extra fluid lost in the patients must have derived primarily from the interstitial space. During alteration in Na+ intake, mean blood pressure values were closely related to plasma volume in the patients (r = 0.80, p less than 0.01) but not in controls. Changes in plasma volume in the head-up tilt position were assessed from the hematocrit values. During tilting, the blood pressure in controls was unchanged, but their plasma volume fell by 10.3% +/- 1.8% (p less than 0.001). In contrast, the mean blood pressure of the patients with progressive autonomic failure fell by 40 +/- 6 mm Hg; yet, their plasma volume was unchanged. Thus, in progressive autonomic failure, plasma volume measured during sitting is normal, but dynamic regulation of plasma volume during salt restriction or orthostasis is abnormal and hypovolemia is offset by partitioning of interstitial fluid into the plasma. Also, because the blood pressure is unusually dependent on volume, this fluid redistribution could be an important defense against severe hypotension in patients lacking cardiovascular reflex control.

Supine hypertension, blood pressure variability and circadian rhythm in autonomic failure: the role of ambulatory intra-arterial monitoring

Blood pressure variation over 24 h was studied in twelve subjects with suspected or established autonomic failure using ambulatory intra-arterial monitoring. Three subjects who had been previously diagnosed as having orthostatic hypotension due to autonomic failure were found to have normal circulatory reflexes. A generally consistent circadian variation of blood pressure was seen in the other nine subjects, pressure rising gradually from its lowest point early in the morning to a peak during the early part of the night; this pattern was also found during bed rest in four subjects. Supine hypertension (an hourly mean blood pressure of greater than 170/90 mmHg) not suspected from sphygmomanometric readings was observed in four subjects, generally during the night. Heart rate variability was reduced in six subjects while short-term blood pressure variability was markedly increased.

Growth hormone response to clonidine is impaired in patients with central sympathetic degeneration

Serum growth hormone (GH) levels before and after intravenous clonidine (1.5 mcg/Kg) were measured in normal subjects and patients with chronic idiopathic autonomic failure (AF) due to central sympathetic degeneration. Normal subjects showed a rise in plasma GH from 2 +/- 1 mU/l to 27 +/- 12 mU/l. Basal levels were similar but there was no rise in GH levels in the AF patients. There was no difference in sedation in the two groups, indicating similar central nervous system penetration of the drug. Systolic blood pressure fell in both groups. Diastolic blood pressure fell significantly in normals but not in the AF patients. Clonidine-induced growth hormone release may be a potentially useful neuroendocrine marker indicating derangement of certain components of the central alpha-adrenergic system in man.

Non-obstructive detrusor failure. A urodynamic, electromyographic, neurohistochemical and autonomic study

Twenty-eight patients presenting with persistent loss of the voiding reflex have been evaluated. Those with cauda equina lesions or pelvic nerve injury were distinguished from a group with idiopathic detrusor failure by their abnormal urethral behaviour during filling, and by urethral sphincter electromyography (EMG). Bladder muscle biopsies revealed the presence of presumptive cholinergic fibres in all three groups, indistinguishable in quantity and distribution from normal controls. The implications of these findings for the diagnosis and management of these patients is discussed.

Circadian variation of blood pressure in autonomic failure

We have monitored ambulant intra-arterial blood pressure with the Oxford system in six subjects with autonomic failure who exhibited postural hypotension. Plotting pooled hourly mean values we have demonstrated a consistent circadian trend in blood pressure that was the inverse of the normal pattern, with the highest pressures at night and the lowest in the morning. In four subjects, confinement to bed did not substantially alter this pattern. Heart rate variability was much reduced in four of the subjects, but relatively normal in two in whom blood pressure variation was also less abnormal. There was a correlation of the nadir of the blood pressure measurements with the reported time of peak incidence of orthostatic symptoms. These findings are of importance in both the management and physiologic testing of patients with this condition.

"Claudication" of the sciatic nerve

Images

Blood pressure and vasopressin in progressive autonomic failure. Response to postural stimulation, L-dopa and naloxone

We showed previously that patients with progressive autonomic failure with multiple system atrophy (MSA) failed to excrete a water load while they were standing, suggesting abnormal postural regulation of vasopressin release. The rise of plasma arginine vasopressin (AVP) with upright posture is modulated by central dopamine and opioid receptors. Patients with MSA may have depletion of brain dopamine and opioid peptides. We measured the plasma levels of AVP in patients with MSA and control subjects during postural stimulation by head-up tilt and the inhibition of this rise in AVP by L-DOPA (dopamine precursor) and naloxone (opiate antagonist). Since L-DOPA and naxolone can alleviate hypotension, we also studied the effects of these agents on orthostatic hypotension. Plasma AVP concentration of normal subjects rose progressively over 90 min of head-up tilt and this postural rise in AVP was abolished by L-DOPA and naloxone. Patients with MSA had similar levels of AVP while horizontal. However, they showed a severely blunted postural AVP response since their levels rose to only 10 per cent of the rise in the normal subjects despite the additional stimulus to AVP secretion of considerable postural hypotension. They also showed no inhibition of AVP secretion by L-DOPA or naloxone. Naloxone did not alter the blood pressure of either group. Although L-DOPA did not change the blood pressure of normal subjects, it lowered it in patients with MSA both while they were horizontal and tilted.

IN CONCLUSION

(1) the postural stimulation of AVP release is blunted in MSA; (2) this postural rise in AVP is not inhibited by a dopamine agonist or opioid antagonist in MSA suggesting loss of dopaminergic and opioid pathways involved in AVP release; (3) endogenous opioids do not contribute to orthostatic hypotension in MSA; (4) patients with MSA are supersensitive to the hypotensive effects of an acute L-DOPA infusion.