Effect of antigen challenge on sensitized guinea pig trachea

Virgin Coconut Oil Supplementation Prevents Airway Hyperreactivity of Guinea Pigs with Chronic Allergic Lung Inflammation by Antioxidant Mechanism

Asthma is a chronic inflammatory disease of the airways characterized by immune cell infiltrates, bronchial hyperresponsiveness, and declining lung function. Thus, the possible effects of virgin coconut oil on a chronic allergic lung inflammation model were evaluated. Morphology of lung and airway tissue exhibited peribronchial inflammatory infiltrate, epithelial hyperplasia, and smooth muscle thickening in guinea pigs submitted to ovalbumin sensitization, which were prevented by virgin coconut oil supplementation. Additionally, in animals with lung inflammation, trachea contracted in response to ovalbumin administration, showed a greater contractile response to carbachol (CCh) and histamine, and these responses were prevented by the virgin coconut oil supplementation. Apocynin, a NADPH oxidase inhibitor, did not reduce the potency of CCh, whereas tempol, a superoxide dismutase mimetic, reduced potency only in nonsensitized animals. Catalase reduced the CCh potency in nonsensitized animals and animals sensitized and treated with coconut oil, indicating the participation of superoxide anion and hydrogen peroxide in the hypercontractility, which was prevented by virgin coconut oil. In the presence of L-NAME, a nitric oxide synthase (NOS) inhibitor, the CCh curve remained unchanged in nonsensitized animals but had increased efficacy and potency in sensitized animals, indicating an inhibition of endothelial NOS but ineffective in inhibiting inducible NOS. In animals sensitized and treated with coconut oil, the CCh curve was not altered, indicating a reduction in the release of NO by inducible NOS. These data were confirmed by peribronchiolar expression analysis of iNOS. The antioxidant capacity was reduced in the lungs of animals with chronic allergic lung inflammation, which was reversed by the coconut oil, and confirmed by analysis of peribronchiolar 8-iso-PGF2α content. Therefore, the virgin coconut oil supplementation reverses peribronchial inflammatory infiltrate, epithelial hyperplasia, smooth muscle thickening, and hypercontractility through oxidative stress and its interactions with the NO pathway.

Structure of the guinea-pig trachea at rest and in contraction

The trachea of the guinea-pig measures about 47.5 mm in situ, and it shrinks to 38 mm when excised. It can be stretched to the in situ length with a load of 2-4 grams. The transverse area of its lumen measures about 4.5 mm2 in the cervical portion, whereas in the lowermost thoracic portion it measures 2.8 mm2, a difference of 37%. The lumen has an oval shape with the transverse diameter always exceeding the sagittal diameter. The separation between the ends of a cartilage in the dorsal region of the trachea is greater in the cervical than in the thoracic region. Elastic fibres are abundant in the tunica propria and run longitudinally; the collagen is in some areas arranged with a criss-cross pattern. The muscle is inserted on the concave aspect of each cartilage at some distance from the ends of the cartilage and it is therefore much longer than the gap between cartilage ends. Upon contraction in vitro (induced by carbachol) the muscle shortens by about 50%; there is a marked decrease of the transverse diameter of the trachea, and a certain decrease also of the sagittal diameter due to a straightening of the muscle and a change in shape and a movement of the mucosa. The cartilage ends are brought together and in the thoracic region they are bent and overlap extensively. The lumen of the trachea becomes circular and its area is reduced to 2.2 mm2 in the cervical portion and 1.7 mm2 in the thoracic portion.

Effects of tryptamine antagonists on the anaphylactic contractions of the bovine pulmonary smooth muscles

Calves were sensitized with horse plasma (H.P.), 0.2 ml/kg, i.v., and H.P. (0.2 ml/kg) in Freund's complete adjuvant, s.c. The latter injection was repeated 1 week later and the animals were killed 10 days after the second injection. Spirally cut strips of pulmonary artery and vein and the trachealis muscle from the sensitized calves contracted to 5-hydroxytryptamine (5-HT) and specific antigen (horse plasma). Antigen-induced contractions of the pulmonary smooth muscles were significantly blocked (P less than 0.05) by the 5-HT antagonists, methysergide and ketanserin. The trachea, however, appeared less sensitive to the antagonists than the pulmonary vessels. The results suggest that 5-HT participates in the pulmonary anaphylactic reactions of cattle and that ketanserin may be useful in suppressing bovine pulmonary hypersensitivities.

Studies on an isolated innervated preparation of guinea-pig trachea

An isolated preparation of the guinea-pig trachea with intact parasympathetic and sympathetic innervation has been devised. Responses to nerve stimulation were recorded as increases or decreases in intraluminal pressure from the fluid-filled trachea. The preparation maintained a positive resting intraluminal pressure of 3-4 cmH2O. This was unaffected by atropine, hexamethonium or propranolol. Brief pressor responses, which could be completely blocked by atropine or hexamethonium, were obtained by applying short trains of stimuli to the cervical segment of the right vagus. The amplitude of responses was frequency-dependent up to a maximum at 40 Hz. Depressor responses, more delayed and prolonged than the pressor responses and blocked by propranolol but not by hexamethonium, were obtained by stimulation of the right cervical sympathetic trunk or stellate ganglion in 70% of preparations. Dual pressor-depressor responses were observed in the remaining 30% of preparations. The pressor component was blocked by atropine, the depressor component by propranolol. In the presence of atropine and propranolol, sustained sympathetic stimulation sometimes evoked a small, delayed pressor response which was blocked by phentolamine. Under the same conditions, transmural stimulation produced a depressor response evidently due to non-adrenergic, non-cholinergic nerves. Spontaneous activity was observed in some preparations under normal conditions, but could always be evoked by hypoxia. Responses to sympathetic stimulation were reduced both by hypoxia and during periods of spontaneous activity. 8 The principal advantage of this preparation is that it permits both excitatory and inhibitory responses to be elicited by stimulation of vagal and sympathetic nerves separately in the isolated trachea in the absence of agonist and antagonist drugs.

Reassessment of electrophysiological and contractile characteristics of sensitized airway smooth muscle

Airway smooth muscle preparations were isolated from control guinea pigs, from animals sensitized to albumin and Pertussis vaccine, from sensitized animals which had been resensitized and from animals that had been sensitized and exposed to an inhalation challenge of albumin for 14 days. The resting membrane potential, its changes and contractile response of airway smooth muscle were measured during in vitro antigen challenge, administration of histamine dihydrochloride (10(-3) M), or isoproterenol (10(-3) M). We have found that: (1) The resting membrane potential of normal airway smooth muscle of guinea pig was -61.3 +/- 0.2 mV (+/- SE); (2) Resting membrane potential of airway smooth muscle from sensitized animals was significantly increased (P less than 0.05) to -72.9 +/- 0.3 mV (+/- SE); (3) One week after resensitization of animals a further significant increase (P less than 0.05) in resting membrane potential to -76.2 +/- 0.2 mV (+/- SE) was observed; (4) Resting membrane potential of airway smooth muscle isolated from animals repeatedly exposed to inhalation challenge of antigen significantly decreased (P less than 0.01) to -50.6 +/- 0.5 mV (+/- SE) as compared to controls; (5) After histamine, isoproterenol or antigen administration, the airway smooth muscle from sensitized animals repeatedly exposed to inhalation challenge showed attenuated response (P less than 0.01) as measured by both membrane potential and isometric force. In contrast, the response to antigen and histamine in preparations from sensitized animals is potentiated. It is concluded that both acute sensitization and resensitization on one hand and repeated exposure of sensitized animals to inhaled albumin on the other will alter cellular mechanism(s) responsible for the maintenance of membrane potential and the regulation of excitation-contraction coupling in airway smooth muscle.

Effect of drug treatment and aerosoled antigen sensitization on cyclic AMP and beta adrenergic receptors of guinea pig lung

The interaction between the number of beta adrenergic binding sites and the ability of a beta adrenergic agonist, isoproterenol, to increase cyclic AMP content of guinea pig lung slices was studied. A complex relationship was found. Chronic sensitization of the guinea pig to an aerosol of ovalbumin resulted in lung slices which were hyporesponsive to isoproterenol in vitro, yet possessed an unchanged number of beta adrenergic binding sites. Chronic exposure of guinea pigs to aerosoled isoproterenol or acute treatment with hydrocortisone did not change the number of beta adrenergic binding sites or the responsiveness of the tissue to isoproterenol in vitro. However, chronic hydrocortisone treatment increased the number of binding sites found on the lung slices by 44%, yet there was no change in the responsiveness of the tissue to isoproterenol in vitro. These data suggest that drugs and disease may change the relationship between the various components of the beta adrenergic binding-adenylate cyclase complex of lung.

Alteration of electrophysiological properties of airway smooth muscle from sensitized guinea-pigs

Glass microelectrodes were used to study electrophysiological properties of guinea-pig airway smooth muscle (m. trachealis transversus). The resting membrane potential (Em) of airway smooth muscle was found to be -40.4 +/- 0.5 mV (307 cells, 28 preparations). Twenty-seven percent of all cells successfully impaled showed regular spontaneous electrical activity (amplitude of 2-20 mV, with maximum rate of depolarization 15.0 +/- 2.2 mV . sec-1). Forty-four percent of cells showed irregular fluctuations in Em and the remaining cells showed no electrical activity. All three groups of cells had a similar distribution of individual Em values. The sensitization of animals (14 days incubation period) caused a slight but significant increase (P less than 0.001) in Em to -43.1 +/- 0.9 mV. Repeated daily exposure of sensitized animals to aerosolized albumin for two weeks caused a significant reduction of Em to -27.8 +/- 0.8 mV (P less than 0.001). Five weeks repeated exposure caused a further reduction in Em of airway smooth muscle cells to -22.6 +/- 0.7 mV (P less than 0.001). The responses to both histamine (10(-4) M) and isoprenaline (5 x 10(-6) M), as gauged by changes in Em, were altered in the trachea of chronically exposed guinea-pigs. The changes in airway smooth muscle electrical properties were related to the number of times the animals were exposed to inhaled antigen. Even after two weeks of daily exposure, the changes were marked. Airway smooth muscle alteration may be important in the pathogenesis of bronchial asthma.

Some characteristics of the purinergic nervous system in normal and sensitized airway smooth muscle

Supramaximal electrical field stimulation was employed to produce biphasic response in segments of cervical and thoracic tracheas and in first generation of bronchi isolated from guinea pigs. This response consists of contraction (as measured by maximal active tension, ATmax) followed by relaxation (as measured by maximal active relaxation, ARmax). First, the effect of electrical stimulation was studied in relation to frequency and duration of impulse. Highest degree of relaxation (ARmax) was achieved with a frequency of stimulus of 40 pulses per sec for segments of trachea, and 60 pulses per sec for first generation bronchi, and with duration of pulse of 1.0 msec for segments of trachea, and 2.0-2.5 msec for bronchi, and with duration of pulse of 1.0 msec for segments of trachea, and 2.0-2.5 msec for bronchi. Secondly, mean length-tension relationship was determined. It was found that maximal relaxation (ARmax) occurred at 160 +/- 5% of Lmax in case of tracheal segments and 160 +/- 2% of Lmax for bronchial preparations. Using propranolol pretreatment (10(-4) M), which inhibited participation of adrenergic receptors in relaxation, it was determined that approximately 50% relaxation of airway smooth muscle of the normal guinea pig is mediated through the purinergic nervous system. Both tracheas and bronchi isolated from sensitized guinea pigs, chronically exposed to antigen, showed a significant decrease in overall relaxation (P less than 0.01). However, the per cent decrease in relaxation after propranolol was not different in sensitized animals than that found in controls. The data suggest that relaxation of segments of airways isolated from animals chronically exposed to antigen is decreased in consequence of alterations in both purinergic and adrenergic nervous systems.

Effects of ketamine and halothane on normal and asthmatic smooth muscle of the airway in guinea pigs

In vitro preparations of trachea isolated from normal and asthmatic guinea pigs were used to measure their maximum contractile response to histamine challenge and to determine spontaneous relaxation of smooth muscle of the airway. The effect of ketamine and halothane on these reactions was investigated. The optimal ketamine concentration was found to be 10 micrograms/ml. This dose attenuated the maximum contraction and produced greater relaxation (p less than 0.01) of isolated trachea. However, ketamine failed to prevent an anaphylactic (Schultz-Dale) response when antigen (one per cent albumin) was added in an experimental chamber containing pre-sensitized guinea pig trachea. In contrast, halothane abolished any response to histamine challenge and prevented development of the Schultz-Dale response of smooth muscle from the airway of asthmatic guinea pigs.

Role of glucose in contractility of airway smooth muscle

This study investigated the response of isolated tracheal preparation (ITP) from guinea pigs to three bronchoconstrictive drugs: histamine (H), carbachol (CAR), and acetylcholine (ACH). Cumulative dose-response curves were obtained in substrate-rich (5.50 mM of glucose) and substrate-free physiological salt solutions under aerobic conditions (PO2 = 95 +/- 0.5 Torr) or in acute 30-min hypoxia (PO2 = 30 +/- 2 Torr). The reactivity of ITP was measured by ED50 (effective dose developing 50% of maximal response); and the contractility of ITP was measured by a maximal developed isometric tension. This study showed that the contractile response of isolated segments of tracheas to H, CAR, and ACH was significantly decreased (P less than 0.05) when the experimental medium contained no glucose, or when glucose was replaced with metabolic inhibitor 2-deoxyglucose. This data contrasted with findings obtained with main pulmonary arteries (MPAs) isolated from the same species, where the absence of glucose in the experimental medium did not affect patterns of histamine cumulative dose-response curves. It was also shown that pretreatment of isolated tracheas with a small dose of insulin significantly decreased (P less than 0.05) the contractile response of airway smooth muscle to histamine. In both experiments, either with or without glucose in the experimental medium, acute hypoxia (30 min) had a significantly greater effect (P less than 0.05) on the development of isometric tension of MPA compared with that on ITP. Both removal of glucose from the experimental medium and/or acute hypoxia significantly decreased (P less than 0.001) adenosin triphosphate and creatine phosphate contents of tracheal segments but did not influence the high-energy phosphate content of main pulmonary arteries exposed to similar conditions. In addition to pointing out the physiological and metabolic differences between pulmonary vascular and airway smooth muscle, this study showed the important dependence of airway smooth muscle on glucose as a substrate.

The Schultz-Dale reaction: a review

Vascular (pulmonary and hepatic blood vessels) and nonvascular (gastro-intestinal, reproductive and respiratory systems) smooth muscle preparations obtained from specifically sensitized animals of numerous species including man contract to specific antigen in vitro (Schultz-Dale phenomenon). This immunopharmacological technique is a useful tool to demonstrate immediate-type hypersensitivity in actively or passively sensitized tissues and may be used to investigate the nature of the principal pharmacological mediators involved in a particular tissue as well as to screen anti-anaphylactic (anti-allergic) drugs. However, much remains to be investigated on the complex mechanisms of action of antigen, desensitization and resensitization (recovery) of anaphylactic responsiveness.

Autacoid and anaphylactic reactivity of pulmonary and hepatic smooth musculature of the cat

Histamine, 2-methylhistamine (2-MeH: a relatively specific H1 receptor agonist), 5-HT, carbachol, bradykinin (BK) and PGF2alpha contract isolated cat pulmonary vein, artery and hepatic vein. PGE1, PGF2alpha and 4-methylhistamine (4-MeH: a relatively specific H2-receptor agonist) contract pulmonary arterial strips but further increase in the dose of PGE1 produces relaxation. Isoproterenol relaxes partially contracted blood vessels at low doses, but contracts at high doses. Cat trachea contracts to 5-HT, acetylcholine and carbachol but is insensitive to histamine, its analogues, BK and PGF2alpha. However, partially contracted trachea relaxes to histamine, 4-MeH, 2-MeH, isoprenaline, BK, PGE1, E2 and F2alpha. PGF2alpha and SRS-A contract cat bronchus. Isoprenaline, PGE1 and E2 relax cat bronchus contracted to carbachol, 5-HT, PGF2alpha, SRS-A and antigen. The in vitro anaphylactic contraction (Schultz-Dale reaction) of isolated pulmonary and hepatic veins, bronchus and trachea from horse plasma sensitized cat suggested the involvement of lung and liver in anaphylaxis of the cat.