Enhanced lung C-fiber responsiveness in sensitized adult guinea pigs exposed to chronic tobacco smoke.

Tobacco smoke (TS) exposure induces bronchoconstriction and increases airway secretions and plasma extravasation in certain sensitive individuals, particularly those with asthma. C-fiber activation also induces these effects. Although the mechanism by which chronic TS exposure induces airway dysfunction is not well understood, TS exposure may enhance C-fiber responsiveness. To investigate the effect of chronic TS exposure on C-fiber responsiveness to capsaicin and bradykinin, especially in atopic individuals, we exposed ovalbumin (OA)-sensitized guinea pigs to TS (5 mg/l air, 30 min/day for 7 days/wk) or to compressed air. Nonsensitized guinea pigs were also exposed to either compressed air or TS. Beginning after 120 days of exposure, C fibers and rapidly adapting receptors (RARs) were challenged with capsaicin and bradykinin. TS exposure enhanced sensory receptor and airway responsiveness to both intravenous capsaicin and bradykinin challenge. C-fiber, RAR, and airway responsiveness to capsaicin challenge was greatest in OA-sensitized guinea pigs exposed to TS. OA alone induced capsaicin hyperresponsiveness at 5 microg. Airway responsiveness to bradykinin was also greatest in OA-sensitized guinea pigs exposed to TS. OA alone enhanced C-fiber responsiveness to bradykinin at 5 and 10 microg. C-fiber activation by either agonist appeared direct, whereas RAR activation appeared indirect. Therefore, a mechanism of airway hyperirritability induced by the combination of OA sensitization and chronic TS exposure may include hyperirritability of lung C fibers.

Chronic tobacco smoke exposure increases cough to capsaicin in awake guinea pigs.

Chronic exposure to irritants such as tobacco smoke (TS) can induce spontaneous and enhanced irritant-induced coughing, especially in asthma. To determine if the mechanism of enhanced coughing involves activation of capsaicin-sensitive sensory receptors (C-fibers), we exposed both non-sensitized (NS) and ovalbumin-sensitized guinea pigs to TS (5 mg/L air, 30 min exposure, and 7 days/week). Similar groups were exposed to compressed air. After 90 days of exposure, we challenged the airways with capsaicin, bradykinin, histamine and methacholine. Capsaicin induced coughing as well as bronchoconstriction in guinea pigs exposed to TS. In ovalbumin (OA) guinea pigs coughing and bronchoconstriction were enhanced. Tachykinin receptor antagonists attenuated coughing to both capsaicin and acute TS challenge. Bradykinin also induced coughing and bronchoconstriction in guinea pigs exposed to TS. There was no statistical separation between the two TS groups however. Histamine and methacholine induced similar bronchoconstriction but fewer coughs in all four experimental groups. In conclusion, chronic TS exposure induced coughing to capsaicin and bradykinin challenge. The effect of capsaicin was further enhanced in OA guinea pigs. Enhanced coughing induced by TS exposure likely involves activation of capsaicin-sensitive sensory C-fibers and neuropeptide release with possible subsequent activation of rapidly-adapting receptors.

Chronic tobacco smoke exposure increases airway sensitivity to capsaicin in awake guinea pigs.

Tobacco smoke (TS) exposure induces airway hyperreactivity, particularly in sensitive individuals with asthma. However, the mechanism of this airway hyperreactivity is not well understood. To investigate the relative susceptibility of atopic and nonatopic individuals to TS-induced airway hyperreactivity, we exposed ovalbumin (OA)-sensitized and nonsensitized guinea pigs to TS exposure (5 mg/l air, 30-min exposure, 7 days/wk for 120-156 days). Two similar groups exposed to compressed air served as controls. Airway reactivity was assessed as an increase in enhanced pause (Penh) units using a plethysmograph that allowed free movement of the animals. After 90 days of exposure, airway reactivity increased in OA-TS guinea pigs challenged with capsaicin, bradykinin, and neurokinin A fragment 4--10 aerosols. In addition, substance P content increased in lung perfusate of OA-TS guinea pigs in response to acute TS challenge compared with that of the other groups. Airway hyperirritability was not enhanced by phosphoramidon but was attenuated by a cocktail of neurokinin antagonists, nor was airway hyperreactivity observed after either methacholine or histamine challenge in OA-TS guinea pigs. Chronic TS exposure enhanced neither airway reactivity to histamine or methacholine nor contractility of isolated tracheal rings. In conclusion, chronic TS exposure increased airway reactivity to capsaicin and bradykinin aerosol challenge, and OA-TS guinea pigs were most susceptible to airway dysfunction as the result of exposure to TS compared with the other groups. Increased airway reactivity to capsaicin suggests a mechanism involving neurogenic inflammation, such as increased activation of lung C fibers.

Sensory receptor activation by mediators of defense reflexes in guinea-pig lungs.

Histamine and bradykinin are mediators released within the lungs during lung defense. Both pulmonary rapidly-adapting receptors (RARs) and afferent C-fibers have been suggested to initiate defense reflexes evoked by these mediators. However, it is not known whether the sensory endings are directly stimulated by these mediators rather than indirectly by mechanical changes. Therefore, pulmonary RARs and C-fibers were challenged with aerosols of histamine, bradykinin and capsaicin in anesthetized guinea pigs. During histamine challenge tracheal pressure (PTr) and RAR nerve activity (NA) increased concurrently. After isoproterenol administration to attenuate increases in PTr, histamine-induced increases in RAR NA were similarly attenuated. Results with bradykinin or capsaicin challenge were similar. Therefore activation of RARs by histamine, capsaicin and bradykinin was dependent upon changes in lung mechanics. C-fibers were activated by capsaicin or bradykinin prior to any changes in PTr. However, C-fibers were not affected by histamine challenge despite substantial increases in PTr. C-fibers are activated directly by either capsaicin or bradykinin but not by histamine.

Pulmonary C-fiber activation before and after peptidase inhibition in rats.

Inhibition of peptidases within the lungs not only potentiates the effects of neuropeptides released from C-fibers but also the effects of bradykinin and capsaicin both of which stimulate C-fibers. To determine if peptidase inhibition potentiates C-fiber activation, we challenged pulmonary C-fibers in rats with capsaicin or bradykinin before and after inhibition of neutral endopeptidase (NEP) or angiotensin converting enzyme (ACE). Inhibition of NEP by phosphoramidon (10 mg/kg, i.v.) potentiated the effect of capsaicin (0.5-1 micrograms, i.v.) on C-fiber activity but did not change the response to bradykinin (1-2 micrograms, i.v.). Inhibition of ACE by captopril (5 mg/kg, i.v.) potentiated C-fiber activation by either bradykinin or capsaicin. Aerosol administration of either phosphoramidon (1 x 10(-5) M, 2 min) or captopril (4.6 x 10(-3) M, 2 min) potentiated C-fiber activation by capsaicin aerosol (1.6 x 10(-4) M, 1 min) but not by bradykinin aerosol (9.4 x 10(-5) M, 1 min). Therefore, inhibition of NEP or ACE may potentiate airway obstructive mechanisms initiated by C-fiber stimulation.

Identification of vagal sensory receptors in the rat lung: are there subtypes of slowly adapting receptors?

1. We studied the characteristics of pulmonary sensory receptors whose afferent fibres are in the left vagus nerve of opened-chest rats. The activity of these receptors was recorded during mechanical ventilation approximating eupnoea, as well as during deflation, stepwise inflations and constant-pressure inflations of the lungs. Data were also collected from closed-chest rats and analysed separately. 2. Ninety-four per cent of receptors were located in the ipsilateral lung or airways with the remainder in the contralateral lung. 3. Not only were slowly adapting receptors (SARs) the most abundant pulmonary receptors but 21% of them were either exclusively or predominantly active during the deflationary phase of the ventilatory cycle. Deflationary units were found in opened- and closed-chest rats. The average conduction velocity for all fibres innervating SARs averaged 29.7 m s-1. 4. We found rapidly adapting receptors (RARs) to be extremely rare in the rat. Their activity was sparse and irregular. The conduction velocities of fibres innervating RARs averaged 12.3 m s-1. 5. Far more abundant than RARs in the remaining population of pulmonary fibres were C fibres. They were observed to have an average conduction velocity of 2.1 m s-1, base-level activity which was irregular and a high pressure threshold of activation and were stimulated by intravenous capsaicin injection. 6. Notable differences exist between pulmonary receptors in rats and those reported in other species. The variations include the abundant existence of intrapulmonary SARs with exclusively deflationary modulation and the rarity of RARs. We also encountered C fibres which have not previously been described systematically in the rat.

Platelet-activating factor induces nonspecific desensitization to bronchodilators in guinea pigs.

Platelet-activating factor (PAF) is a potent mediator of inflammation and is a mediator which is known to cause airway hyperresponsiveness in human and experimental animals. However, the mechanism of action of PAF is not clear. In this study we examined the effect of methacholine upon specific airway resistance (SRaw) in guinea pigs and the ability of either isoproterenol or prostaglandin E2 to reverse this effect both before and after PAF administration at sub-bronchoactive doses in conscious guinea pigs as well as in isolated airway tissues. SRaw in conscious guinea pigs was monitored using a whole-body plethysmograph. In nonsensitized guinea pigs, a concentration of PAF (0.1 micrograms/ml), which by itself did not affect SRaw, potentiated the methacholine-induced increase in SRaw. In ovalbumin-sensitized animals, the response to methacholine was significantly greater as compared to the nonsensitized group. Prior administration of PAF did not potentiate the response to methacholine in ovalbumin-sensitized animals. In isolated tracheal rings and lung parenchymal strips of nonsensitized guinea pigs, preincubation of the tissue with 0.1 microM PAF decreased the sensitivity of isoproterenol to induce relaxation. However, in the ovalbumin-sensitized group of guinea pig tracheas or lung parenchymas, PAF did not reduce further the effect of isoproterenol to elicit relaxation. Furthermore, PAF did not alter the affinity or the density of beta adrenoceptors in guinea pig lung membranes. These data suggest that PAF may potentiate the responses to bronchoconstrictors and desensitize the responses to bronchodilators in a nonspecific manner. This may be a mechanism underlying PAF-induced airway hyperresponsiveness in asthma.

Antagonism of airway reactivity induced by ovalbumin antigen in guinea pigs by 5-amino-4-imidazolecarboxamide riboside.

The effect of 5-amino-4-imidazolecarboxamide riboside (AICA riboside), a modulator of purine metabolism, was studied on antigen-induced bronchospasm in ovalbumin (OA)-sensitized guinea pigs. In separate experiments, sodium cromoglycate (SCG) and terbutaline were used to compare their effectiveness with that of AICA riboside (wt/vol). AICA riboside and SCG were administered as an aerosol daily for a minimum of 2 weeks before OA aerosol challenge. Terbutaline, as an aerosol, was administered once 5 minutes before OA challenge. Airway reactivity was determined through the use of a whole-body plethysmography by monitoring specific airway resistance (SRaw). OA aerosol challenge of 0.05%, 0.1%, and 0.25% (wt/vol), administered for a period of 1 minute, increased SRaw. Each of the three agents attenuated the effect of OA on SRaw, although terbutaline demonstrated more consistency and potency as compared to either AICA riboside or SCG. However, at moderate degrees of OA challenge, AICA riboside appeared to be as effective as either agent. Although the mechanism of action of AICA riboside remains uncertain, it may have therapeutic benefit in the treatment of asthma or allergic diseases.

Attenuation of antigen-induced bronchoconstriction in guinea pigs by a new xanthine derivative (HWA448).

We examined the effect of a new xanthine derivative, HWA448, on antigen-induced bronchoconstriction in actively sensitized guinea pigs. Guinea pigs were sensitized by intraperitoneal injection of bovine serum albumin (BSA) on two occasions, separated by 10 days. Two weeks after the second injection, the animal was placed in a two-chambered whole body plethysmograph and specific airway resistance (SRaw) was monitored for 10 min after an aerosol inhalation of BSA. HWA448 prevented the increase in SRaw after challenge (at 5 and 20 mg/kg i.p.). Aminophylline also prevented the increase in SRaw at 20 mg/kg, but not at a 5-mg/kg dose. The concentration of HWA448, which produced 50% relaxation of the tracheal rings constricted with 0.1 mM of histamine, was 49.9 microM as compared with 18.2 microM in aminophylline. HWA448 has a protective effect on antigen-induced bronchoconstriction in guinea pigs and may be a useful agent in the therapy of bronchial asthma.

The ventilatory movements of the avian pelvis and tail: function of the muscles of the tail region of the pigeon (Columba livia).

We have observed that birds of several different taxa move their tails in conjunction with sound production. These observations suggested to use that tail movements might also be associated with ventilation. Since we hypothesized that rhythmic movements of the tail and pelvis will ventilate the lungs, the activities of tail, epaxial and cloacal muscles of the pigeon were examined. Electromyograms (EMGs) were recorded from these muscles while ventilation was monitored. A muscle was considered to have ventilatory activity when the EMG activity had an obvious correlation to either inspiration or expiration. To obtain further information about the correlation between muscular activity and ventilation, we induced hyperpnea by administering 5% CO2. We report that the tail muscles that function as expiratory muscles are the M. caudofemoralis, the M. pubocaudalis internus and the M. pubocaudalis externus. We refer to these as the suprapubic abdominal muscles to distinguish them from the infrapubic (ventral) abdominal muscles. These muscles depress the pelvis and the uropygium and compress the thoracoabdominal cavity. M. transversus cloacae functions as an expiratory muscle by protracting the cloaca or by reducing its compliance. Of the suprapubic muscles we studied, the only inspiratory muscle is the axial muscle, M. longissimus dorsi. M. longissimus dorsi acts at the notarial-synsacral junction to elevate the pelvis. The rocking movements of the notarial-synsacral joint appear to be important for ventilation during conditions in which the sternum is 'fixed', such as when the bird is resting on its breast. We suggest that a division of labor may exist between the infra- and suprapubic abdominal muscles during ventilation such as panting or vocalization.

Capsaicin challenge, reflex bronchoconstriction, and local action of substance P.

Capsaicin was administered as an aerosol to unanesthetized guinea pigs in a whole body plethysmograph and intravenously to anesthetized guinea pigs to investigate its mechanism of action. Capsaicin increased specific airway resistance in the unanesthetized guinea pigs and increased insufflation pressure in anesthetized guinea pigs. To investigate the possible reflex action of capsaicin, an atropine or lidocaine aerosol was administered before the capsaicin aerosol challenge in unanesthetized guinea pigs. Both lidocaine and atropine reduced the effect of capsaicin. However, neither intravenous atropine nor bilateral vagotomy antagonized the effect of injected capsaicin in the anesthetized guinea pigs. To investigate further the possible action of capsaicin, spantide (a substance P receptor antagonist) was administered before capsaicin challenge. Spantide injection in anesthetized guinea pigs attenuated the effects of the intravenous capsaicin challenge. In unanesthetized guinea pigs spantide pretreatment, as an aerosol, did not ameliorate the effects of a capsaicin aerosol challenge. However, intraperitoneal administration of spantide did reduce the effect of the capsaicin aerosol challenge as the specific airway resistance increased. Therefore, capsaicin produced its effects independent of vagal reflexes, although reflex actions of capsaicin could have occurred through other pathways. Reflex actions of capsaicin, however, were demonstrable only in the unanesthetized guinea pig. Because spantide attenuated the effect of capsaicin, increased insufflation pressure and specific airway resistance due to capsaicin challenge in both unanesthetized and anesthetized guinea pigs may be attributed, at least in part, to capsaicin's induction of substance P release or the release of other tachykinins.

Activity of rapidly-adapting receptors to histamine and antigen challenge before and after sodium cromoglycate.

Sodium cromoglycate (SCG) blocks histamine release from sensitized mast cells challenged by antigen in vitro. Yet, not all the observed effects of SCG in vivo can be explained by this mechanism alone. Rapidly-adapting or "irritant" receptors (RAR) are thought to mediate reflex bronchoconstriction. Others have proposed that SCG may desensitize these receptors to histamine. We administered aerosols of histamine (100 micrograms/ml given for 3 min) before and after SCG (20 mg/ml aerosol for 5 min) to adult, mongrel dogs. SCG did not reduce the increase in tracheal pressure or RAR activity in response to histamine challenge. We also administered aerosols of Ascaris suum antigen (7 min) to dogs which had shown a positive skin reaction to subepidermal injection of this antigen. SCG attenuated both the increase in tracheal pressure and RAR nerve activity in response to the antigen challenge. These findings suggest that SCG does not affect the activity of the RAR or decrease the tracheal pressure in response to histamine challenge in an anesthetized dog, whereas SCG is effective in decreasing the response of both these parameters to antigen challenge when given prophylactically presumably by stabilizing the mast cell membrane.

Rapidly-adapting receptor activity and intratracheal pressure in guinea pigs. I. Action of leukotriene C4.

Leukotriene C4 (LTC4) is a major component of slow-reacting substance of anaphylaxis (SRS-A) and is a potent bronchoconstrictor. In humans LTC4 results in bouts of coughing which suggests stimulation of pulmonary receptors involved in a reflex mechanism. Furthermore, atropine reduces the effect of both LTC4 and SRS-A. To test the hypothesis that LTC4 stimulates the rapidly-adapting or "irritant" receptor (RAR) of the airways, we administered LTC4 by both intravenous injection (10-1000 ng) and by aerosol delivery (1 microgram/ml) to the lungs of guinea pigs while recording arterial blood pressure, intratracheal pressure, and nerve activity from RARs. LTC4 (i.v.) concurrently increased both nerve activity and intratracheal pressure even at low doses in a dose-dependent manner. Therefore, a direct action of LTC4 (i.v.) upon the RAR is difficult to conclude. The separation of peak tracheal pressure and peak nerve activity was apparent with aerosol delivery of LTC4. The pattern of RAR activity during LTC4 aerosol challenge was unrelated to respiratory phase. FPL 55712 blocks the effects of SRS-A. We challenged the lung with 500 ng LTC4 intravenously before and after FPL 55712 injection (2.5 mg/kg). FPL 55712 blocked the increases of both tracheal pressure and RAR activity.

Rapidly-adapting receptor activity and intratracheal pressure in guinea pigs. II. Action of aspirin and salicylic acid in antagonizing mediators of allergic asthma.

The effects of leukotriene C4 (LTC4), prostaglandin F2 alpha (PGF2 alpha), histamine, and bradykinin upon intratracheal pressure and nerve activity from rapidly-adapting receptors (RARs) before and after the nonsteroidal anti-inflammatory drugs salicylic acid (SA) and aspirin (ASA, acetylsalicylic acid) have been studied in guinea pigs. All mediators increased tracheal pressure and nerve activity in a time-dependent manner. The peak in nerve activity always preceded the peak in tracheal pressure. Neither SA or ASA blocked the effects of histamine or PGF2 alpha upon tracheal pressure or nerve activity. ASA and even SA blocked the effects of bradykinin on both parameters. While SA had no effect on LTC4, ASA blocked the effects of LTC4 upon both tracheal pressure and nerve activity. These results suggest that both LTC4 and bradykinin may act through mediators derived from arachidonic acid not only in increasing tracheal pressures but also to increase RAR nerve activity.

Effect of prostaglandin F2 alpha on pulmonary rapidly-adapting-receptors in the guinea pig.

Pulmonary rapidly-adapting-receptors ( RARs ) are sensory nerve endings whose afferent fibers can be recorded in the vagus nerve. RARs may play a role in reflex bronchoconstriction as seen in anaphylaxis. They can be stimulated by chemical mediators of anaphylaxis, such as prostaglandin F2 alpha (PGF2 alpha). PGF2 alpha aerosol was administered to saline and bovine serum albumin (BSA)-treated guinea pigs while recording the activity of RARs . PGF2 alpha (250 micrograms/ml) given for 7-13 minutes increased both tracheal pressure and nerve activity over that produced by saline exposure in untreated guinea pigs. PGF2 alpha administered for three minutes (5-100 micrograms/ml) increased RAR nerve activity in a dose-related manner in the first five minutes of the experiment only in the BSA treated guinea pigs. Since changes in tracheal pressure did not show a significant dose-response relationship, the RARs responding to PGF2 alpha seemed to be stimulated by a direct mechanism. No correlation was shown between tracheal pressure and RAR nerve activity during PGF2 alpha treatment. Whereas, a significant correlation was found between tracheal pressure and RAR nerve activity during histamine aerosol treatment (r = 0.985). Histamine aerosol (1 to 1000 micrograms/ml, 3 min.) increased intratracheal pressure for 3 out of 4 doses. RAR nerve activity increased significantly only at the highest dose. Therefore, a possible direct effect of PGF2 alpha upon RARs exists while the effect of histamine seems dependent upon changes in airway pressure in the guinea pig.

Characterization of intrapulmonary, rapidly adapting receptors of guinea pigs.

The activity of 33 afferent vagal fibers arising from rapidly adapting pulmonary stretch receptors in the lungs of 21 guinea pigs was studied. These receptors were identified by their response to constant pressure hyperinflation and to negative pressure deflation of the lungs. The response was irregular bursts of action potentials with an adaptation index greater than 70% in 2s. Little or no activity was noted in these receptors during eupneic breathing. The conduction velocity of the afferent fibers from these receptors ranged from 3.1 to 57.1 m/s (mean = 20.2 +/- 5.1 SD). Receptors were stimulated by intravenous injection of histamine and also by vapors of ether, alcohol, acetone, ammonia, and cigarette smoke. Stimulation by the inhalation of the vapors usually occurred in the absence of any change in tracheal pressure or even when the tracheal pressure became slightly lower than before vapor challenge, thus suggesting a direct action. If an increase in tracheal pressure occurred, the discharge of the receptor began well in advance. However, stimulation of the receptor by histamine was always accompanied by significant increases in tracheal pressure. Isoproterenol prevented the increase in tracheal pressures produced by histamine challenge. In addition, isoproterenol blocked the response of rapidly adapting receptors to histamine as well. Isoproterenol had no effect on receptor response to the various vapors used in this study. Therefore, stimulation of rapidly adapting receptors by histamine seems to be dependent on an increase in tracheal pressure, while a direct action in indicated by several 'irritant' gases. The characteristics of the rapidly adapting receptors in guinea pig lungs are more closely related to the irritant receptor of the rabbit and the cat than to the rapidly adapting receptors in lungs of dogs.

Lung compliance and cholesterol during stellate ganglion stimulation.

The relationships between lung compliance, surface tension, and cholesterol during stimulation of the sympathetic nervous system were studied in 28 cats. Cats were anesthetized with ketamine hydrocholoride, injected with one of five sympathetic blocking agents or inhibitors and injected with isoprotenol. The left stellate ganglion was then stimulated electrically for 5 min. We found that stimulation decreased lung compliance and increased the surface tension and the cholesterol concentration in the lung wash fluid. Alpha blockers (phentolamine and phenoxybenzamine) and catecholamine inhibitors (reserpine and guanethidine) prevented these changes, but the beta blocker practolol did not. In additional experiments airway resistance, functional residual capacity and lung weights did not change during stellate stimulation. The results from the present study suggest that stellate ganglion stimulation resulted in decreased lung compliance with an increased surface tension and cholesterol in lung wash fluid.

Effects of prostaglandins E1 and E2 on activity in laryngeal and pharyngeal afferent fibers.

Prostaglandins (PG) E1 and E2 were applied topically to the receptive fields of feline laryngeal and pharyngeal sensory receptors, while action potentials were recorded from single - or few-fiber preparations of the superior laryngeal nerve. When initially dissolved in ethanol, PGs stimulated these sensory receptors. If ethanol was not used as a solvent for the PGs they did not stimulate the sensory receptors. Similarly, local application of dilute (0.025%, v/v) solutions of ethanol alone excited the receptors, whereas phosphate buffer alone did not. Thus PGE1 and PGE2 do not themselves stimulate sensory receptors in the larynx and pharynx. These findings suggest that irritant properties of PGEs on upper airways are attributable to the ethanol used as a solvent.

Hyperbaric oxygen and pulmonary surface tension.

Previous work has shown that short-term exposure of cats to oxygen at high pressure (OHP), to the extent of overt convulsive seizures, has little or no effect on the lung appearance or lung weight but does alter the alveolar surfactants. More prolonged exposure results in hemorrhagic edema of the cat lung similar to that observed in rats after only short-term exposure. Previous work showed that sympathetic stimulation via the stellate ganglion and mechanical CNS injury results in altered surfactants attributed to increased intra-alveolar cholesterol. In the present study, cats exposed to OHP until the animals convulsed intermittently for 3 min (approximately 1 hour, 6 ATA) similarly showed altered surfactants with a high minimum surface tension and a 150% increase in intra-alveolar cholesterol. These changes also occurred in the absence of any gross lung injury. The results from the present study suggest that an important causal mechanism involved in the development of gross lung injury associated with prolonged OHP exposure is an initial increase in minimum surface tension due to increased intra-alveolar cholesterol.