J receptor activity in idiopathic pulmonary hypertension and its expected change in the presence of pulmonary bed vasodilators.

Juxtapulmonary receptors (J) lying in the lung parenchyma are stimulated naturally by any condition that produces interstitial oedema, transient increases in interstitial volume and pressure or raised pulmonary capillary pressure. There is no information available about the level of their stimulation in patients with idiopathic pulmonary hypertension (IPH) who have high levels of pulmonary artery systolic pressures. The aim of the present study therefore was to find the level of these receptors activity in these patients at their prevailing pulmonary artery systolic pressures. This was done by the established method of determining the dose of i.v. lobeline that gives rise to threshold levels of sensations in the upper chest areas and accelerates respiration. In IPH patients it was found to be as high as 31.6 ± 5.6 µg/kg i.e., twice as much as that known for healthy individuals which is 15 µg/kg. This shows an enhanced stimulation of J receptors in IPH patients. Expectedly when pulmonary artery systolic pressure falls with pulmonary bed vasodilator medication given to IPH patients, a reduction in the natural stimulus of J receptors would also occur leading to a fall in their activity and hence that of the quantum of their reflexes of respiratory acceleration and inhibition of exercise. This finding provides the first insight of a neural mechanism that could be influenced to produce its effects when pulmonary artery systolic pressure falls by pulmonary vasodilator medication.

Low activation threshold of juxtapulmonary capillary (J) receptors of the lung.

Respiratory reflexes arising from stimulating juxtapulmonary capillary (J) receptors by increasing doses of phenyl diguanide (PDG) were examined in 18 spontaneously breathing cats. In 60% an immediate and four-fold increase in breathing frequency (fR) was produced by doses as small as 5.1 ± µg/kg (range: 3.5-7.5) thus establishing that a significant increase in fR is produced by J receptors by stimulating them with minimal or threshold doses of PDG. In response to similar minimal doses of PDG J receptor afferent activity increased accompanied by acceleration of breathing rate. The response to supra threshold doses was either an apnoea followed by rapid shallow breathing (rsb) or to an apnoea preceded by rsb or only to rsb. Respiratory excursions counted from high-speed run records of intrapleural pressure revealed that the apnoeic response obtained in some cases was a phase of high-frequency breathing and not its suspension. These findings using a chemical stimulus demonstrate that J receptors, with some variability, have a very low threshold for stimulation resulting in notable respiratory acceleration. Thus their afferent output could increase significantly at low intensities of their physiological stimuli such as rise in cardiac output and incipient pulmonary congestion that are generated with mild exercise, to give rise to augmented breathing which is consequently seen.

Dyspnea in Eisenmenger syndrome and its amelioration by sildenafil: role of J receptors.

BACKGROUND: In Eisenmenger syndrome (ES), oral phosphodiesterase type-5 inhibitors, which are preferential pulmonary vasodilators, reduce the elevated pulmonary artery pressure and pulmonary vascular resistance index by increasing cyclic guanosine monophosphate (cGMP). However, no information is available as to how pulmonary vasodilatation alleviates the accompanying dyspnoea and improves patient's exercising ability. OBJECTIVES: As the natural stimulus of juxtapulmonary capillary (J) receptors is an increase in interstitial pressure, the aim was to estimate their threshold level stimulation chemically by intravenous lobeline, before and after 6 weeks of sildenafil therapy in treatment-naive ES patients. METHODS: Nine Eisenmenger syndrome patients [mean age=26 (SD=1.6) years] underwent 6MWT and an exercise test before and 6 weeks after oral sildenafil (20mg 3× D). Their respiratory responses to threshold doses of intravenous lobeline were determined at both these stages. RESULTS: After 6 weeks of sildenafil therapy, the 6MWD [from 453.3 (SD=50.9) m to 516.6 (SD=48.9) m; P=0.001] and the duration of exercise with the modified Bruce protocol from 7 min 53 s (SD=0.04) to 10 min 44 s (SD=0.88) (P=0.001) improved significantly. However, the improvement in oxygen saturation was not noteworthy. The lobeline dose required to produce threshold level of respiratory effects was higher in ES patients [37.5 (SD=3.4) µg/kg] and with sildenafil therapy it fell significantly [20.6 (SD=1.8) µg/kg; P=0.001]. CONCLUSIONS: J receptor threshold doses were elevated in ES patients and fell significantly with sildenafil therapy that was associated with improved exercise tolerance, implying thereby a role of J receptors in producing dyspnea in ES patients.

Characteristics of thermostable endoxylanase and ß-xylosidase of the extremely thermophilic bacterium Geobacillus thermodenitrificans TSAA1 and its applicability in generating xylooligosaccharides and xylose from agro-residues.

An extremely thermophilic bacterial isolate that produces a high titer of thermostable endoxylanase and ß-xylosidase extracellularly in an inducible manner was identified as Geobacillus thermodenitrificans TSAA1. The distinctive features of this strain are alkalitolerance and halotolerance. The endoxylanase is active over a broad range of pH (5.0-10.0) and temperatures (30-100 °C) with optima at pH 7.5 and 70 °C, while ß-xylosidase is optimally active at pH 7.0 and 60 °C. The T 1/2 values of the endoxylanase and ß-xylosidase are 30 min at 80 °C, and 180 min at 70 °C, respectively. The endoxylanase activity is stimulated by dithiothreitol, but inhibited strongly by EDAC and Woodward's reagent K. N-BS and DEPC strongly inhibited ß-xylosidase. MALDI-ToF (MS/MS) analysis of tryptic digest of ß-xylosidase revealed similarity with that of G. thermodenitrificans NG 80-2, and suggested that this belongs to the GH 52 glycosyl hydrolase super family. The action of endoxylanase on birch wood xylan and agro-residues such as wheat bran and wheat straw liberated xylooligosaccharides similar to endoxylanases of the family 10 glycoside hydrolases, while the enzyme preparation having both endoxylanase and ß-xylosidase liberated xylose as main hydrolysis product.

Thermostable and alkalistable endoxylanase of the extremely thermophilic bacterium Geobacillus thermodenitrificans TSAA1: cloning, expression, characteristics and its applicability in generating xylooligosaccharides and fermentable sugars.

Xylanase encoding gene (1,224 bp) from Geobacillus thermodenitrificans was cloned in pET28a (+) vector and successfully expressed in Escherichia coli BL21 (DE3). The deduced amino acid sequence analysis revealed homology with that of glycosyl hydrolase (GH) 10 family with a high molecular mass (50 kDa). The purified recombinant xylanase is optimally active at pH 9.0 and 70 °C with T(1/2) of 10 min at 80 °C, and retains greater than 85 % activity after exposure to 70 °C for 180 min. The enzyme liberates xylose as well as xylooligosaccharides from birchwood xylan and agro-residues, and therefore, this is an endoxylanase. The xylan hydrolytic products (xylooligosaccharides, xylose, and xylobiose) find application as prebiotics and in the production of bioethanol. The xylanase being thermostable and alkalistable, it has released chromophores and phenolics from the residual lignin of pulps, suggesting its utility in mitigating chlorine requirement in pulp bleaching.

Effect of sublingual nitrate on respiratory reflexes arising from stimulation of juxta-pulmonary capillary (J) receptors by i.v. lobeline and short duration exercise.

Juxta-pulmonary capillary (J or pulmonary C fiber) receptors are stimulated by an increase in pulmonary blood flow and give rise to respiratory acceleration and related sensations and inhibit exercise. However, the reverse, i.e., the effect of reducing pulmonary blood flow on their reflexes, is as yet not known. This was investigated by carrying out a placebo-controlled study on the acute effects of a single dose (0.4 mg) of sublingual glyceryl nitrate (GTN), known to shift blood from the central to the peripheral circulation, on the respiratory parameters of exercising healthy subjects and on their responses to i.v. lobeline. In 10 subjects, GTN use delayed the first appearance of respiratory sensations from 9.08 ± 0.9 min to 11 min (P=0.002), reduced the increase in minute ventilation by the end of 10 min of exercise (P=0.003) and increased its duration by 1-4s and doubled it in the remaining one subject. In a majority of 8 of them, the effect of GTN on i.v. lobeline-induced respiratory reflexes and sensations was a significant increase in the dose required (P=0.006) for producing threshold effects and in the latency of their appearance (P=0.003). The latter feature points to a reduction in blood flow in the lung parenchyma where these receptors are located and to which they are sensitive. As this would have led to a reduced stimulation of these receptors, it would account for the delayed appearance of respiratory symptoms, a reduction in ventilatory increase and prolongation of exercise duration. We demonstrated a mechanism of reducing the stimulus level of J receptors by reducing pulmonary blood flow by means of pharmacological sequestration with GTN use, which then led to a reduction in the magnitude of respiratory and viscerosomatic reflexes, while noting at the same time that changes in blood flow in the pulmonary bed do not directly influence limb muscles, tendons and joints which also determine exercise output.

Evoked corticospinal output to the human scalene muscles is altered by lung volume.

Increases in lung volume inhibit the inspiratory output from the medulla, but the effect of lung inflation on the voluntary control of breathing in humans is not known. We tested corticospinal excitability using transcranial magnetic stimulation (TMS) to evoke a response in the scalene muscles. TMS was delivered at rest at three different lung volumes between functional residual capacity (FRC) and total lung capacity (TLC) during incremental inspiratory and incremental expiratory manoeuvres. Motor evoked potentials (MEPs) in scalenes were ∼50% larger at a high lung volume (FRC+∼90% inspiratory capacity [IC]) compared to lower lung volumes (FRC and FRC+∼40% IC) in both inspiratory and expiratory manoeuvres (p<0.001). The change in MEP size was not due to differences in pre-stimulus EMG amplitude (p=0.29). The results suggest a differential effect of lung inflation on the automatic and voluntary control of breathing in humans.

Influence of codeine on lobeline-induced respiratory reflexes and sensations and on ventilation with exercise in healthy subjects.

In 15 healthy subjects, the effect of 60 mg oral codeine and placebo was examined on intravenously injected lobeline-elicited respiratory reflexes and sensations. Its influence was also studied on ventilation and appearance of distressful respiratory sensations with modest but incremental exercise. After placebo, tachypnoea and respiratory sensations were evoked with 12.1 ± 1.9 µg/kg of lobeline i.v. (mean threshold dose) and after codeine, by significantly higher doses i.e., 18.0 ± 3.1 µg/kg (P < 0.05). Additionally after codeine, in response to incremental doses of lobeline the respiratory reflex was notably attenuated and the magnitude of respiratory sensations, subdued. Dry cough seen in 66% of the subjects with suprathreshold doses of lobeline i.e., 22.0 ± 3.4 µg/kg (mean), appeared post codeine, with significantly higher doses i.e., 27.0 ± 3.9 µg/kg (mean) (P < 0.05) and in a fewer subjects (60%). Mean increase in minute ventilation at the end of 8 min of incremental treadmill walking after codeine was 21% less than after placebo (P < 0.05); 60% of the subjects continued to walk for an additional 4 min and the onset of respiratory discomfort was delayed by 1-5 min. This is the first report of an attenuation of lobeline-elicited respiratory reflexes and sensations that are attributable to J receptors (pulmonary C fibres) by a pharmacological entity. It also suggests that codeine decreased these receptors' known contribution to respiratory augmentation and motor inhibition during exercise, which was seen as a delay in the onset of, and a decrease in the magnitude of respiratory discomfort during treadmill walking and an increase in the duration walked by more than half the subjects.

Influence of lower body negative pressure release on soleus H reflex, respiratory sensations and reflexes in human subjects.

Using a physiological model of acutely increasing venous return into the lungs, i.e. by applying and then releasing lower body negative pressure (LBNP) to mimic the natural stimulus of juxtapulmonary capillary (J) or pulmonary C fibre receptors, produced an immediate and significant reduction in the amplitude of the Hoffman (H) reflex by 81±4% (P=0.001) in a majority of subjects 70% (n=5). Accompanying this was a notable change in the respiratory pattern with tidal volume (V(T)) increasing in all subjects from (mean) 0.462±.038 to 0.777±.061l/min (P=0.001) and the respiratory rate (F(R)) in 40% from 14±1 to 24±0.8 breaths/min. A feeling of pressure in throat, upper chest was reported by all and a shortness of breath-by 70% of the subjects. These were similar in nature to the respiratory sensations felt with threshold doses of intravenous lobeline, a well-established chemical stimulant of J receptors. All effects lasted for 15-20s and within a minute the parameters resumed their earlier control values. In animals, respiratory augmentation and locomotion inhibition are well-established reflexes of J receptors - this simultaneous though transitory reduction in H reflex amplitude reflecting change in the excitability of the motoneurone pool and appearance of respiratory effects, is the first demonstration in human subjects of the two reflexes appearing in response to a sudden increase in pulmonary blood flow that mimics the natural stimulus of these receptors.

Early symptom-relief after valvulotomy in mitral stenosis indicates role of lobeline-sensitive intrapulmonary receptors.

Respiratory sensations of eight patients with mitral stenosis in response to i.v. lobeline and 6-min walk before percutaneous mitral valvulotomy (PMV) were 'being short of breath', pressure in chest, tracheo-bronchial irritation, a desire to cough, persistent dry cough, chest pain and were qualitatively similar amongst 75% (P=0.005) of the patients. A week after PMV lobeline evoked similar sensations but the threshold dose decreased from 32.4+/-3.8 to 24.1+/-3.2 microg/kg (P=0.001) and pulmonary artery wedge pressure (PAwP), signifying reduction in pulmonary congestion, from 23.1+/-1.4 to 14.3+/-3.4 mm Hg (P<0.001). Distance walked in 6 min increased from 217+/-58 to 319+/-51.6m; and mitral valve area from 0.63+/-0.01 to 1.43+/-0.26 cm(2) (P<0.001). A fall in lobeline-sensation threshold dose indicated reduction in pulmonary congestion and stimulus to juxtapulmonary/J (or pulmonary C fibre) receptors which suggests that they had contributed to the respiratory and viscerosomatic symptoms seen before PMV.

How does lobeline injected intravenously produce a cough?

In order to examine, whether the lobeline-induced cough is a true reflex or a voluntary effort to get rid of its irritating sensations in the upper respiratory tract, we systematically studied the cough response to lobeline, of subjects who were unable to make conscious discriminations i.e. were either comatose (n=4) or anaesthetized (n=5). 8 microg/kg lobeline injected into the right atrium of one and 29 microg/kg intravenously (i.v.) into another evenly and spontaneously breathing comatose subject produced a cough after 4s and 12s, respectively. Cough was repeatable and showed a dose response relationship i.e., its latency decreasing and its duration/intensity increasing with the dose. In a third subject, capable only of weak spontaneous respiration, a relatively high dose injected into the right atrium (44 microg/kg) generated a pronounced cough-like respiratory movement superimposed on the artificial ventilation and also during the apnoea after disconnecting the pump. No respiratory response was evoked in a fourth subject who had no evidence of brainstem reflexes. In five normals, cough was elicited with a mean dose of 35+/-5 microg/kg i.v. (latency 14+/-2 s; duration 10+/-3 s). After thiopental anaesthesia, injecting 41+/-7 microg/kg produced a cough within 13+/-2 s that lasted for 12+/-2 s. It may be noted that neither the later dose nor the latency or duration of cough that it produced were significantly different from the pre anaesthesia values (P>0.05). These two sets of results show unequivocally that the lobeline-induced cough is evoked reflexly; its magnitude in the conscious state could vary by subjective influences. We discuss the likelihood of its origin from juxtapulmonary capillary receptors.

Presence of lobeline-like sensations in exercising patients with left ventricular dysfunction.

Since there is evidence that lobeline-induced sensations, associated with discomfort in the mouth, throat and chest arise by stimulating juxtapulmonary or J receptors, we were interested in investigating if similar sensations are felt by patients with left ventricular dysfunction (LVD) in whom a natural stimulation of these receptors would occur by transient interstitial oedema or during augmentation of the stimulus, by increased pulmonary blood flow during exercise. Threshold doses of lobeline produced three or more respiratory sensations simultaneously in 9 out of 10 patients, which was greater than the response of the controls (P < 0.01). With mild exercise, a greater number of patients (7) than controls (1) reported feeling two or more sensations (P < 0.01); in fact half the controls did not express a respiratory sensation with equivalent exercise (P < 0.05). The predominant lobeline-like sensations reported by patients with exercise were a feeling of heat or burning and pressure in the throat or chest (P < 0.05). The presence of cough in three patients and in none of the controls was noteworthy. The mean latency with which sensations appeared during exercise in patients (4.4 +/- 0.3 min) was almost half that in controls (7.4 +/- 0.2 min) (P < 0.005). Since, respiratory sensations in response to lobeline and exercise were intensified in patients compared to controls and since both lobeline and exercise-induced sensations were similar (P < 0.05), we speculate that a common origin exists. Despite important caveats, that we discuss, in our view these respiratory sensations and cough arise from stimulation of J receptors.