Effects of NOS inhibition on the cardiopulmonary system and brain microvascular markers after intermittent hypoxia in rats.

We previously demonstrated that rats subjected to intermittent hypoxia (IH) by exposure to 10% O(2) for 4 h daily for 56 days in a normobaric chamber, developed pulmonary hypertension, right ventricular hypertrophy and wall-thickening in pulmonary arterioles, compared with normoxic (N) controls. These changes were greater in rats subjected to continuous hypoxia (CH breathing 10% O(2) for 56 days). Cerebral angiogenesis was demonstrated by immunostaining with glucose transporter 1 (GLUT1) antibody, in viable vessels, in CH and to a lesser degree in IH. In this study, adult Wistar rats were subjected to the same hypoxic regimes and given the nitric oxide synthase (NOS) inhibitor N(6)-nitro-L-arginine methyl ester (L-NAME) in drinking water (NLN, IHLN and CHLN regimes) to induce hypertension. There was significant systemic hypertension in NLN and IHLN rats, compared with N and IH, but surprisingly not in CHLN compared with CH. Hematocrit rose in all hypoxic groups (up to 79% in CHLN). There was no significant pulmonary hypertension in IHLN versus NLN rats, although there was asymmetric wall thickening in pulmonary arterioles. Cerebral GLUT1 immunoreactivity increased with L-NAME, with or without hypoxia, especially in CHLN rats, but conspicuously there was no evidence of angiogenesis in brains of IHLN compared with NLN rats. NOS blockade may attenuate the cerebral and pulmonary vascular changes of IH while augmenting cerebral angiogenesis in continuous hypoxia. However, whether cerebral effects are due to systemic hypertension or changes in cerebral nitric oxide production needs to be evaluated.

A double-blind, randomised, controlled Phase II trial of Heliox28 gas mixture in lung cancer patients with dyspnoea on exertion.

Helium has a low density and the potential of reducing the work of breathing and improving alveolar ventilation when replacing nitrogen in air. A Phase II, double-blind, randomised, prospective, controlled trial was undertaken to assess whether Heliox28 (72% He/28% O(2)) compared with oxygen-enriched air (72% N(2)/28% O(2)) or medical air (78.9% N(2)/21.1% O(2)) could reduce dyspnoea and improve the exercise capability of patients with primary lung cancer and dyspnoea on exertion (Borg >3). A total of 12 patients (seven male, five female patients, age 53-78) breathed the test gases in randomised order via a facemask and inspiratory demand valve at rest and while performing 6-min walk tests. Pulse oximetry (SaO(2)) was recorded continuously. Respiratory rate and dyspnoea ratings (Borg and VAS) were taken before and immediately post-walk. Breathing Heliox28 at rest significantly increased SaO(2) compared to oxygen-enriched air (96+/-2 cf. 94+/-2, P<0.01). When compared to medical air, breathing Heliox28 but not oxygen-enriched air gave a significant improvement in the exercise capability (P<0.0001), SaO(2) (P<0.05) and dyspnoea scores (VAS, P<0.05) of lung cancer patients.

Adverse pulmonary vascular effects of high dose tricyclic antidepressants: acute and chronic animal studies.

Overdose of tricyclic antidepressants, which inhibit cellular serotonin (5-HT) uptake, sometimes causes acute respiratory syndrome-like symptoms. Their acute and chronic cardiopulmonary actions, which might be implicated, utilising both in vivo and ex vivo animal studies, were investigated in this study. Acute amitriptyline (AMI), iprindole and imipramine caused dose-dependent prolonged rises in pulmonary artery pressure and oedema in anaesthetised cats in vivo. Acute AMI, in isolated ex vivo blood-perfused rat lungs, also caused dose-dependent sustained vasoconstriction, which could be attenuated with either calcium channel inhibition or a nitric oxide donor. It was demonstrated that the pressor effects of AMI were not due to release of histamine, serotonin, noradrenaline, or the activities of cycloxygenase or lipoxygenase. After AMI, hypoxic pulmonary vasoconstriction and the pressor actions of 5-HT and noradrenaline were diminished, possibly due to uptake inhibition. Activities of the endothelial-based enzymes, nitric oxide synthase and endothelin-converting enzyme, were undiminished. Large acute doses of AMI caused oedema with rupture of capillaries and alveolar epithelium. Chronic iprindole raised pulmonary artery pressure and right ventricle (RV)/left ventricle (LV) + septal (S) weight. Chronic AMI led to attenuation of the pressor action of 5-HT, especially when associated with chronic hypoxic-induced pulmonary hypertension. RV/LV+S weight increased, attributable to LV decline. The acute and chronic effects observed might have relevance to clinical overdose, while the attenuation of acute effects offers possible therapeutic options.

Effects of radiographic contrast media on pulmonary vascular resistance of normoxic and chronically hypoxic pulmonary hypertensive rats.

Intravascular radiographic contrast media (RCM) can be associated with significant morbidity in patients with pulmonary hypertension (PH). This study investigated the direct effect of the four main classes of RCM (high osmolar ionic monomer "diatrizoate"; low osmolar ionic dimer "ioxaglate"; low osmolar non-ionic monomer "iopromide"; and iso-osmolar non-ionic dimer "iotrolan") in ex vivo isolated rat lungs perfused with blood at 20 ml min(-1) under basal conditions (air + 5% CO2 ventilation, pulmonary artery pressure (Ppa) 16-20 mmHg) and when Ppa was raised by hypoxic vasoconstriction in normal rats (2-3% O2+5% CO2 ventilation, Ppa increased by 4-14 mmHg). The effects of low osmolar RCM (ioxaglate, iopromide and iotrolan) were also studied in rats with PH induced by chronic hypoxia (3 weeks 10% O2, Ppa 26-36 mmHg). Increasing volumes (0.05 ml, 0.1 ml, 0.3 ml, and 0.5 ml) of RCM, mannitol (osmolar and pH control) or normal saline (volume control) were added to the 10 ml blood reservoir (n=4-9 per group). In normal rats, RCM caused a dose-dependent slow rise in Ppa. The maximum rise in mean+/-SEM Ppa at the cumulative dose of 0.95 ml was ioxaglate 13.8+/-1.6 mmHg>iotrolan 7.3+/-1.7 mmHg=diatrizoate 9.8+/-2.2 mmHg>iopromide 3.0+/-0.8 mmHg (p<0.05). The rise in Ppa induced by ioxaglate and iotrolan was significantly greater than in the mannitol and saline controls (p<0.05). Pre-treatment with endothelin receptor A/B blockade (SB209670) did not abolish the rise in Ppa induced by diatrizoate (0.95 ml) in the normal rat (3.8+/-1.3 mmHg diatrizoate alone and 3.4+/-1.1 mmHg in the presence of 40 microM SB209670, n=5 per group). When Ppa was raised by acute hypoxia, ioxaglate and diatrizoate (0.5 ml) caused a fall in Ppa (percentage fall -53+/-23 and -118+/-10, respectively, p<0.001) while iotrolan and iopromide caused a small further rise in Ppa, which was significant with iotrolan at a dose of 0.3 ml (percentage rise in pressure 14.2+/-2.3, p<0.05). In chronic pulmonary hypertensive rats, RCM (0.95 ml) caused an overall slow progressive rise in Ppa (iopromide 6.8+/-1.7 mmHg< ioxaglate 11.6+/-2.5 mmHg=iotrolan 12.7+/-1.1 mmHg). However, ioxaglate initially induced an acute fall of Ppa (maximum fall 4.22+/-0.9 mmHg, p<0.05) for almost 20 min. In summary, iopromide induced the least change in Ppa of normal and pulmonary hypertensive rats. The pathophysiology of the effects of RCM on the pulmonary circulation remains uncertain.

The acute effects of dexfenfluramine on human and porcine pulmonary vascular tone and resistance.

STUDY OBJECTIVES: Treatment with anorectics has become an important aspect of care for the severely obese. One such anorectic, the phenylethylamine dexfenfluramine (dFen), has been associated with the development of pulmonary hypertension. It works by reducing the neuronal uptake of 5-hydroxytryptamine (5-HT; serotonin) through inhibition of the 5-HT transporter. In this study we investigated whether dFen has a direct vasoconstrictor action on human and porcine pulmonary vasculature. DESIGN: For the human study, tissue was obtained from patients who had undergone lung and heart-lung transplantation. The effect of dFen was studied in seven isolated colloid perfused human lungs and in rings of human pulmonary artery (PA) dissected from the lungs of a further 19 patients. For the porcine study, regional pulmonary vascular resistances (PVRs) were measured in isolated perfused porcine lungs. Vasoconstriction was assessed following dFen alone and in combination with hypoxia, cyclo-oxygenase blockade (indomethacin, 10(-5) mol/L), or nitric oxide synthase (NOS) blockade (N(G)-nitro-L-arginine, 10(-5) mol/L). RESULTS: In the human study, 5-HT and dFen caused only limited increases in tension of isolated rings of PA. The concentration of dFen, 10(-4) mol/L, that was needed to increase tension was higher than that found normally in treated patients where peak levels are 3. 3 x 10(-7) mol/L. Other vasoconstrictors such as prostaglandin F(2)alpha, 10(-5) mol/L, and the thromboxane analog U46619, 10(-6) mol/L, produced far greater increases in tension. Ketanserin, 10(-4) mol/L, attenuated the constrictor response to 5-HT but had no effect on the constrictor response to dFen. Removal of the endothelium did not influence the response to dFen. In the isolated ventilated and perfused lungs, dFen caused an increase in PVR again only at a comparatively high concentration, 10(-4) mol/L. In the porcine study, dFen, 10(-4) mol/L, did not increase any PVR during normoxia or following NOS blockade. Small insignificant increases in PVR occurred during hypoxia and after cyclo-oxygenase blockade. CONCLUSION: These results do not support the view that dFen would act as a direct vasoconstrictor when given in the usual doses. However, delayed elimination of dFen could raise tissue concentrations to high levels and give rise to vasoconstriction and pulmonary hypertension.

Combined microlightguide spectrophotometry and microendoscopy for measurement of oxygen saturation in peripheral nerves.

Microlightguide measurements of the spectral composition of backscattered light may be used to determine local tissue oxygen saturation and monitor tissue perfusion using intravenous injection of fluorescein dye as a contrast agent. We have used a combination of microlightguide spectrophotometry and microendoscopy to measure intravascular oxygen saturation (HbSaO2%) and monitor blood flow in the sciatic nerve of 12 healthy male Sprague-Dawley rats. The microlightguide and endoscope combination is a relatively new measurement technique. The aims of this study were to determine whether microlightguide spectrophotometry and microendoscopy could be used to measure HbO2 and blood flow in peripheral nerves and to compare the measurements made using the flexible lightguide with the endoscope-lightguide combination. We found no significant difference between the two types of measurement over similar regions of the nerve. mean SaO2% values 77.1% (95% CI = 75.4-78.8) and 78.8% (95% CI = 77.5-80.1) respectively. During a period of hypoxia there was a similar fall in both arterial and nerve oxygen saturation. Following injection of fluorescein, the rate of increase in nerve fluorescence was used as a measure of perfusion. The combination of microlightguide spectrophotometry and microendoscopy allows the exact site of measurement to be directly visualized. The minimally invasive nature of this technique may allow its application to the study of peripheral nerves in human subjects in conditions such as diabetic neuropathy where vascular factors are thought to have an important role in aetiology.

The effect of antihistamine, endothelin antagonist and corticosteroid prophylaxis on contrast media induced bronchospasm.

Bronchospasm is a well recognized adverse reaction to radiographic contrast media (RCM) and may occur more frequently in asthmatics and atopics. This study was designed to identify RCM which are most likely to cause bronchospasm and to investigate underlying mechanisms mediating this response. Guinea pigs (mean body weight 550 g, n = 46) were anaesthetized with Hypnorm (5 ml kg-1) and Hypnovel (2 ml kg-1) and tracheal, jugular and pleural cannulae introduced. Total airways resistance (Raw) was calculated from the slope of the pressure/flow relationship. The effects of RCM (diatrizoate 370 mgI ml-1, ioxaglate 320 mgI ml-1, iotrolan 300 mgI ml-1 and iopromide 300 mgI ml-1) at a dose of 4 ml kg-1 body weight or control solutions matched for volume, pH and osmolarity administered via the jugular vein on Raw were studied. The effects of pre-treatment (30 min before the administration of RCM) with antihistamine (Mepyramine (30 mg kg-1 i.p.)) or non-selective endothelin receptor antagonist (SB209670 (1 mg kg-1 i.v.)) were investigated. The effectiveness of corticosteroids prophylaxis (prednisolone (20 mg kg-1 i.p.)) administered 18-24 h and 1 h pre-RCM was also assessed. Control animals received normal saline pre-treatment before RCM administration. Lungs were taken for histological examination 30-40 min post-administration of RCM. Only ioxaglate caused a significant (p < 0.05) increase in Raw (5.19 +/- 0.58 to 13.95 +/- 3.53 mmHg ml-1 min-1). Neither mannitol nor saline control solutions had any effect on Raw. Pre-treatment with Mepyramine, SB209670 or prednisolone caused no significant change in the ioxaglate induced increase in Raw. Histological examination of lung tissue from ioxaglate treated animals showed no important abnormalities. In summary, only the ionic dimer ioxaglate caused an increase in Raw. This effect was independent of osmolarity and could be the result of the chemical composition of the contrast agent. It was not an inflammatory response and could not be prevented by prophylactic treatment with antihistamine, endothelin antagonist or corticosteroids. The mechanisms responsible for the increase in Raw remain uncertain.

Ventilatory effects of radiographic contrast media.

Respiratory adverse reactions have been reported with the use of contrast media. This study investigates the effects of different radiographic contrast media (RCM) on ventilation and blood gases. Tidal volume and respiratory rate of male Wistar rats anaesthetised with Inactin (100 mg kg-1 intraperitoneally), were measured continuously by integration of tracheal airflow. Contrast media (diatrizoate 370, ioxaglate 320 and iopromide 300) or mannitol controls matched for volume, pH and osmolarity (4 ml kg-1) were administered via a jugular cannula (n > or = 6 per group). Carotid artery blood was sampled at 2, 7, 12, 17, 25 and 30 min post-injection for PaO2, PaCO2 and pH. Systemic blood pressure was monitored from the same cannula. No significant reduction was observed in minute ventilation (tidal volume x respiratory rate per minute) with any of the contrast media. All contrast media and control solutions produced a fall in PaO2 within 4 min; returning to basal levels at 10 min (diatrizoate 35.6% (p < 0.05), ioxaglate 15.2% (p < 0.02), iopromide 16.2% (p < 0.01); controls: 17.3% (p < 0.01), 13.5% (p < 0.02) and 12.0% (NS), respectively). The fall in PaO2 induced by diatrizoate was significantly (p < 0.05) larger in comparison to the other groups. Ioxaglate, iopromide and their mannitol controls induced a comparable fall in PaO2. There was a concurrent rise in PaCO2 and fall in pH that reached significance for diatrizoate (p < 0.01). The changes in blood gases with RCM administration cannot be explained by changes in ventilation and may be due to an effect on pulmonary perfusion.

Capsaicin and neurokinin A-induced bronchoconstriction in the anaesthetised guinea-pig: evidence for a direct action of menthol on isolated bronchial smooth muscle.

1. For many years menthol has been used in the treatment of respiratory disorders although, a bronchodilator effect of menthol has yet to be described. Using the bronchoconstrictors capsaicin (acting via stimulating the release of neuropeptides from sensory afferents) and neurokinin A (NKA) we have raised airways resistance in the guinea-pig (GP) and studied the effect of menthol on both capsaicin and NKA-induced bronchoconstriction in vivo. In vitro the effect of menthol on acetylcholine (ACh) and KCl precontracted GP bronchi was also studied. 2. GP (n = 13) were anaesthetized (urethane 1.5 g kg-1, i.p.) and a bolus injection of capsaicin (7.5 micrograms ml-1, i.v.) or infusion of NKA (1 microgram min-1, i.v.) was given either in the presence of air (0.81 min-1) or air impregnated with menthol vapour (7.5 micrograms l-1) freely breathed from a tracheal cannula via a T-piece. Airways resistance (Raw) and ventilation were measured throughout. Bronchi of mean internal diameter (1029 + 73.6 microns; n = 24) were removed from GP (n = 16) and mounted in the Cambustion myograph. Bronchial rings were maximally precontracted with 80 mM KCl or 2 mM ACh. Relaxation due to a cumulative dose of menthol (1- 3000 microM) was measured. 3. Menthol produced a significant (P < 0.05) 51.3% reversal of the capsaicin-induced increase in Raw, and also inhibited the significant (P < 0.05) reduction in minute ventilation (Ve) associated with the capsaicin-induced increased in Raw. Menthol also caused a significant (P < 0.05) 41% reversal of the NKA-induced increase in Raw. The NKA-induced decrease in Ve was again significantly (P < 0.05) reversed with menthol inhalation. Menthol caused a significant (P < 0.001) dose-dependent relaxation of KCl and ACh precontracted bronchi. 4. We have shown that menthol attenuates both capsaicin and NKA-induced bronchoconstriction in vivo and relaxes KCl and ACh preconstricted bronchi in vitro. Menthol inhibition of NKA and capsaicin-induced bronchoconstriction could be, in part, explained by a direct action of menthol on bronchial smooth muscle.

Effects of radiographic contrast media on the tension of isolated small pulmonary arteries.

The aim of the study was to establish the direct effects of radiographic contrast media (RCM) on the tension of isolated small pulmonary arteries and to investigate any mediation by nitric oxide (NO) and endothelin (ET). Small pulmonary arteries (0.3-0.6 mm in diameter) from male Wistar rats were mounted in a Cambustion vessel myograph and vessel wall tension recorded. The effects of 10, 20, 40, 80, 150, 200 and 250 mgl mI-1 of diatrizoate, ioxaglate, iopromide and iotrolan and their mannitol osmolar control from basal condition, and when the vessels were preconstricted with prostaglandin F2 alpha (PGF2 alpha) either submaximally (10 microM) or maximally (100 microM), were studied. The constrictor response to diatrizoate (40 mgI ml-1) was tested in the presence of non-selective endothelin receptor antagonist (10 microM SB209670). The dilator response to ioxaglate (80 mgI ml-1) was tested in the presence of L-nitroarginine methyl ester (L-NAME, 100 microM). All RCM caused biphasic changes in tension, a small transient fall (dilatation) followed by a sustained rise (constriction). Mannitol caused constriction only. The potency order of constrictions at 10-40 mgI ml-1 was diatrizoate > iopromide > ioxaglate > iotrolan. When the vessels were preconstricted with PGF2 alpha, RCM caused predominantly dilatation; ioxaglate produced the largest effect (-42.1 +/- 3.1%, n = 12). Mannitol caused constriction only. SB209607 had no effect on the constrictor effect of diatrizoate [41.9 +/- 2.3 alone, 42.1 +/- 2.7 with SB209670, n = 10]. L-NAME had no effect on the dilator response to ioxaglate [-38.2 +/- 1.6 alone, -43.6 +/- 2.2 with L-NAME, n = 8]. It is tempting to postulate that dimeric RCM may cause the least changes in the pulmonary circulation during angiography.

Antitussive and antibronchoconstriction actions of fenspiride in guinea-pigs.

Fenspiride is a nonsteroidal anti-inflammatory agent, which we have previously shown to have an in vivo antibronchoconstrictor action in guinea pigs. We have currently studied this action using the constrictors Substance P, neurokinin A, citric acid and capsaicin in anaesthetized guinea-pigs. Fenspiride has also been reported to produce a subjective improvement in cough in patients. We have used a conscious guinea-pig model of cough as a more definitive method to study the effect of fenspiride on capsaicin- and citric acid-induced cough. Aerosolized fenspiride (1 mg.mL-1) caused a 58% reversal of capsaicin-induced bronchoconstriction; and i.v. fenspiride (1mg.kg-1) a 45% reversal of citric acid induced bronchoconstriction. Substance P- and neurokinin A-induced bronchoconstriction were unaffected by 1 mg.kg-1 i.v. fenspiride. Aerosolized fenspiride (1, 3 and 10 mg.mL-1) administered for 4 min reduced citric acid (300 mM) induced cough, but 0.1 mg.mL-1 was without effect. Pretreatment with aerosolized fenspiride (10 mg.mL-1) caused a shift in the citric acid dose response curve to the right. For citric acid-induced cough, the duration of action of aerosolized fenspiride (10 mg.mL-1) was found to be 5 and 15 min post-treatment. Aerosolized capsaicin (30 microM) induced cough was also reduced by 3 and 10 mg.mL-1 aerosolized fenspiride, but no significant effect was found with 1 mg.mL-1. We conclude that aerosolized fenspiride reduces capsaicin- and citric acid-induced bronchoconstriction as well as induced cough in guinea-pigs in vivo. Whether a pathway common to both cough and bronchoconstriction is the site of action of fenspiride remains to be established. We postulate that fenspiride, acting as an antitussive and antibronchoconstrictor agent, would be beneficial in the clinical situation for those patients with hyperresponsive airways.

Effect of fenspiride on pulmonary function in the rat and guinea pig.

1. Fenspiride is an anti-inflammatory agent that may have a role in reversible obstructive airways disease. Small, but significant, improvements have been seen in airways function and arterial oxygen tension in patients with mild chronic obstructive pulmonary disease. These changes have been attributed to the anti-inflammatory properties of the drug. However, airways function can be improved by other means, e.g. improved ventilation/perfusion ratio or reduced airways resistance. The possibility that fenspiride may have actions other than anti-inflammatory was investigated in two animal species. 2. In the rat, actions on the pulmonary circulation were investigated in the isolated perfused lung, but fenspiride proved to be a poor pulmonary vasodilator, showing only a small reversal of the raised pulmonary artery pressure induced by hypoxia. 3. Ventilation was measured in the anaesthetized rat using whole-body plethysmography. Fenspiride caused no increase in ventilation or changes in arterial blood gases. However, a profound hypotensive action was observed with high doses. 4. The possibility that a decrease in airways resistance (R(aw)) might occur with fenspiride was investigated in anaesthetized guinea pigs. Capsaicin (30 mumol/l) was used to increase baseline R(aw) through bronchoconstriction. Fenspiride gave a dose-dependent partial reversal of the raised R(aw), and its administration by aerosol proved as efficacious as the intravenous route. In addition, the hypotensive side-effect found with intravenous injection was alleviated by aerosolized fenspiride.(ABSTRACT TRUNCATED AT 250 WORDS)

The antitussive effects of menthol, camphor and cineole in conscious guinea-pigs.

Menthol and other aromatic vapours have been widely used in the symptomatic treatment of upper respiratory tract infections, although there is little objective evidence as to their benefit. We have investigated the action of aromatic vapours on the cough reflex in conscious guinea-pigs. Animals (n = 13) were pretreated with air or test vapours for 5 min at a rate of 1 l/min. One minute later the animal was challenged with aerosolized citric acid for 2 min. Control responses to air pretreatment were not significantly different throughout the procedures. Three concentrations of each aromatic vapour were used (3, 10 and 30 micrograms/l menthol, 50, 133 and 500 micrograms/l camphor and 0.8, 2.7 and 8 mg/l cineole). Menthol proved the most effective antitussive--10 and 30 micrograms/l produced a significant 28 and 56% reduction in cough frequency--500 micrograms/l camphor gave a significant 33% reduction, while cineole, at the concentrations used, had no significant effect. An increase in cough latency coincided with a reduction in cough frequency. These results demonstrate the efficacy of aromatic vapours as antitussives in chemically induced cough.

A comparative study of the effects of citric acid, capsaicin and resiniferatoxin on the cough challenge in guinea-pig and man.

The cough response following inhalation challenge with the sensory nerve irritant resiniferatoxin was compared with that of capsaicin and citric acid in guinea-pig and man. Capsaicin and citric acid gave comparable dose-response curves in the two species. The mean (+/- SEM) concentration producing five coughs in man was 141.3 (1.3) mM (n = 10) for citric acid and 2.8 (1.3) microM (n = 10) for capsaicin. Those for the guinea-pig were 74.1 (1.2) mM (n = 10) for citric acid and 6.0 (2.4) microM (n = 10) for capsaicin. Resiniferatoxin was active at a lower concentration than either citric acid or capsaicin and maximal tolerable cough response was achieved at concentrations of 3 microM (n = 5) in guinea-pig and 300 nM (n = 1) in man. The cough response to resiniferatoxin was greatly prolonged in both guinea-pig and man. Resiniferatoxin, like capsaicin, caused respiratory distress in the guinea-pig which is linked to bronchoconstriction. Resiniferatoxin probably causes cough by stimulation of capsaicin sensitive neurones.