Thromboxane contributes to the immediate antigenic response of canine peripheral airways

The actions of specific humoral mediators in the immediate response of the canine peripheral airways to antigen challenge are not well understood. Using a method which allows localized exposure of the peripheral lung to antigen, we investigated the role of locally released thromboxane A2 (TxA2) in the immediate response of collateral airways to aerosolized antigen. In dogs with native sensitivity to Ascaris suum antigen, resistance to flow through the collateral system (Rcs) was measured using a wedged bronchoscope technique. Local administration of antigen aerosol (25 microliters, 1:10,000 dilution) produced a gradual increase in Rcs which reached a maximum of 365% of base line in 4-8 min. Analysis of bronchoalveolar lavage fluid obtained from the exposed segment at the peak of the response demonstrated significantly more TxB2 compared with control lavage samples (41.8 +/- 7.8 pg/ml vs. 27.9 +/- 8.3; P less than 0.025). After inhibition of thromboxane synthase with UK-37,248 (3 mg/kg iv) or OKY-046 (5 mg/kg iv), the increase in Rcs was significantly reduced at 40 s (P less than 0.001) and 2 min (P less than 0.01) after antigen delivery, and the maximal increase was attenuated by 41% (P less than 0.005). In contrast, the magnitude and time course of the airway response to aerosols of a stable thromboxane analog (U-46619) were not affected by blockade. Despite a similar attenuation (42%) of the maximal increase in Rcs by sodium meclofenamate (3 mg/kg iv), this cyclooxygenase inhibitor had no effect on the time course of the antigenic response.(ABSTRACT TRUNCATED AT 250 WORDS)     

Measurement of myosin adenosinetriphosphatase and myosin content in cultured heart cells

An assay specific for myosin ATPase in whole-cell extracts of cultured heart cells has been developed. Myosin ATPase is measured by the production of Pi from ATP in the presence of high ionic strength (0.5 M KCl) at pH 9.1. Enzyme activity is maximal with 10 mM CaCl2 and completely inhibited with 5 mM MgCl2. Spontaneously beating myocytes grown in the presence of 10% newborn calf serum and 0.1 mM 5-bromo-2'-deoxyuridine show a significant rise in myosin ATPase between Days 1 and 4 in culture. The measurement of myosin ATPase allows for the quantitation of cellular myosin content, and can be used to assess changes in myosin content that occur during growth, development, and cellular repair.     

Prolonged increased responsiveness of canine peripheral airways after exposure to O3

Because it is relatively insoluble, the oxidant gas O3 may penetrate to small peripheral airways when it is inhaled. Increased responsiveness in large airways after O3 breathing has been associated with the presence of inflammatory cells. To determine whether O3 produces prolonged hyperresponsiveness of small airways associated with the presence of inflammatory cells, we exposed the peripheral lungs of anesthetized dogs to 1.0 ppm O3 for 2 h using a wedged bronchoscope technique. A contralateral sublobar segment was simultaneously exposed to air as a control. In the O3-exposed segments, collateral resistance (Rcs) was increased within 15 min and remained elevated approximately 150% throughout the 2-h exposure period. Fifteen hours later, the base-line Rcs of the O3-exposed sublobar segments was significantly elevated, and these segments demonstrated increased responsiveness to aerosolized acetylcholine (100 and 500 micrograms/ml). There were no differences in neutrophils, mononuclear cells, or mast cells (numbers or degree of mast cell degranulation) between O3 and air-exposed airways at 15 h. The small airways of the lung periphery thus are capable of remaining hyperresponsive hours after cessation of localized exposure to O3, but this does not appear to be dependent on the presence of inflammatory cells in the small airway wall.     

Temporal variability in the responses of individual canine airways to methacholine.

Previous work showed that individual airway size, before any spasmogen, varied widely in the same animals on different days. The effect of this variable baseline size on the airway response to a subsequent challenge is unknown. The present study examined how the variability in individual airway baseline size in dogs was related to that after methacholine challenge on 4 different days using high-resolution computed tomography scans. Dogs were anesthetized and ventilated, and on 4 separate days randomly varying between 1 and 8 wk apart, baseline scans were acquired, followed by a continuous intravenous infusion of methacholine at three rates in increasing order (17, 67, and 200 microg/min). As the measure of variability, we used the coefficient of variation (CV) of the four airway luminal measurements of each airway at baseline and at each dose of methacholine. For most airways, there was wide variability both between and within dogs in the response to a given dose of methacholine (CV = 33-38%). Airways with any level of methacholine stimulation had greater variability than those at baseline. The airway variability was greatest at the lowest dose of methacholine administered but was elevated at all the doses. In conclusion, there was substantial day-to-day variability in baseline airway size. Most importantly, the same dose of methacholine to the same individual airway showed even greater variability than that at baseline. If we consider that increased heterogeneity may potentiate clinical symptoms, then airway response variability may play an important role in the manifestation of airway disease.     

Central role of cyclooxygenase in the response of canine peripheral airways to antigen

We studied the effects of antigen aerosol challenge on the airways of the canine peripheral lung and examined the roles of cyclooxygenase products, histamine, and cholinergic activity in the responses. One-minute deliveries of 1:10,000 or 1:100,000 concentrations of Ascaris suum antigen aerosol through a wedged bronchoscope resulted in mean maximal increases in collateral system resistance (Rcs) of 415 and 177%, respectively, after 4-8 min. Repeated antigen challenge (1:100,000) resulted in significantly decreased responsiveness to antigen after the initial exposure (P less than 0.005). Bronchoalveolar lavage fluid obtained from the isolated, challenged segment had a significant increase in mean (+/- SE) prostaglandin D2 (PGD2) concentration vs. control (222.0 +/- 65.3 vs. 72.7 +/- 19.5 pg/ml; P less than 0.05); histamine concentrations were variable and not significantly different (4.1 +/- 2.6 vs. 1.2 +/- 0.2 ng/ml; P greater than 0.05). In nine experiments, cyclooxygenase inhibition significantly attenuated the antigen-induced increase in Rcs by 53.4% (P less than 0.001), and the concentration of PGD2 in lavage fluid was reduced by 96.0% (P less than 0.01). Blockade of histamine H1-receptors (n = 8) or cholinergic receptors (n = 7) did not significantly affect the airway response (P greater than 0.05). These data indicate that the canine peripheral lung responds in a dose-dependent manner to antigen aerosol challenge and exhibits characteristics of antigen tachyphylaxis. Results also suggest that cyclooxygenase products play a central role in the acute bronchoconstrictive response of the lung periphery.     

Hypocapnia-induced constriction of the canine peripheral airways exhibits tachyphylaxis

Hypocapnia-induced constriction of peripheral airways may be important in regulating the distribution of ventilation in pathological conditions. We studied the response of the peripheral lung to hypocapnia in anesthetized, paralyzed, mechanically ventilated dogs using the wedged bronchoscope technique to measure resistance of the collateral system (Rcs). A 5-min hypocapnic challenge produced a 161 +/- 19% (mean +/- SE) increase in Rcs. The magnitude of this response was not diminished with repeated challenge or by atropine sulfate (1 mg base/kg iv), chlorpheniramine maleate (5 mg base/kg iv), or indomethacin (5 mg/kg iv). The response was reduced by 75% by isoproterenol (5 micrograms/kg iv) (P less than 0.01) and reduced by 80% by nifedipine (20 micrograms/kg iv) (P less than 0.05). During 30-min exposure to hypocapnia the maximum constrictor response occurred at 4-5 min, after which the response attenuated to approximately 50% of the maximum response (mean = 53%, range 34-69%). Further 30-min challenges with hypocapnia resulted in significantly decreased peak responses, the third response being 50% of the first (P less than 0.001). The inability of indomethacin or propranolol to affect the tachyphylaxis or attenuation of the response suggests that neither cyclooxygenase products nor beta-adrenergic activity was involved. Hence, hypocapnia caused a prompt and marked constrictor response in the peripheral lung not associated with cholinergic mechanisms or those involving histamine H1-receptors or prostaglandins. With prolonged exposure to hypocapnia there was gradual attentuation of the constrictor response with continued exposure and tachyphylaxis to repeated exposure both of which would tend to diminish any compensatory effect of hypocapnic airway constriction on the distribution of ventilation.     

A comparison of the dose-response behavior of canine airways and parenchyma

We compared the histamine responsiveness of canine airways and parenchymal tissues in six anesthetized paralyzed open-chest mongrel dogs, partitioning total lung resistance (RL) into airway resistance (Raw) and tissue viscance (Vti). Pressure was measured during tidal breathing (frequency was 0.3 Hz) at the trachea and in three alveolar regions by use of alveolar capsules. Measurements were taken before and after the delivery of increasing concentrations of aerosolized histamine (0.1-30 mg/ml). We found that Vti accounted for 78 +/- 8% of RL under base-line conditions; this proportion remained relatively constant throughout the histamine concentration-response curve. There was a significant correlation between percent change in Vti and percent change in Raw at all levels of histamine-induced constriction (P less than 0.001). Moreover, the sensitivity of the tissues and airways (defined as the concentration of histamine required to double resistance) was remarkably similar. We conclude that, at this frequency of ventilation, Vti accounts for the major portion of RL both under base-line conditions and after histamine-induced constriction. Although increases in RL cannot be attributed solely to events occurring in the airways, the close correlation between changes in Raw and Vti and the similar sensitivities of the two support the use of indexes reflecting changes in airway caliber as an indicator of overall lung histamine responsiveness.