Agents Actions37 (1992)
0065-4299/92/040181-03 $1.50+ 0.20/0 9 1992 Birkhfiuser Verlag, Basel
Repeated aeroallergen challenge induces lung dysfunction but not bronchial hyperresponsiveness in conscious guinea pigs N. Chand 1, K. Nolan, W. Diamantis and R. D. Sofia Wallace Laboratories, Division of Carter-Wallace Inc., Half Acre Rd., Cranbury, NJ 08512, USA
Abstract
Adult male Hartley-strain guinea pigs were sensitized by 10 min exposure to aerosolized 1% ovalbumin (OA; 10 mg/ml in normal saline containing 4% heat-killed B. pertussis vaccine and 0.02% antifoam B emulsion). One week after sensitization, animals were placed in an exposure chamber and challenged (nebulized OA 0.5%) until each animal showed labored breathing. Maximal exposure time was 10 min. Diphenhydramine (20 mg/kg, i.p.) was given 1 h before each OA challenge to protect the animals from bronchospasmic death. Antigen challenge was repeated twice a week for 2 weeks. The specific airway resistance (SRaw) changes in response to increasing concentrations of aerosolized acetyleholine (Ach) were determined. The data obtained in this study demonstrated that repeated antigen challenge produced a significant bronchial tone i.e. an increase in SRaw and a decline in specific airway conductance (SG~w) and failed to induce bronchial hyperreactivity to aerosolized acetylcholine (Ach) in conscious guinea pigs.
Introduction
Bronchial hyperresponsiveness is the main characteristic of asthma. It has been reported that repeated aeroallergen challenge induces airway hyperresponsiveness to aerosolized Ach in actively sensitized, anesthetized guinea pigs [1]. The objective of this study was to produce a model of bronchial hyperresponsiveness by repeated aeroallergen challenge in conscious restrained guinea pigs. Materials and methods
Sensitization procedure Ten male Hartley-strain guinea pigs (CAMM Re1Author for correspondence.
search Laboratory Animals, Wayne, N J) were sensitized by inhalation of an aerosolized 1% ovalbumin solution (OA; 10 mg/ml in normal saline containing 4% heat-killed B. pertussis vaccine and 0.02% antifoam B emulsion, 10 min, 15 psi) [1].
Chronic repeated antigen challenge One week after sensitization, diphenhydramine (20 mg/kg, i.p.) was given 1 h before each challenge to protect the animals from anaphylactic death. Animals were placed in the exposure chamber and exposed to nebulized 0.5% OA solution until each animal exhibited labored breathing and increased respiratory rate. The maximal exposure time was 10 min. Antigen challenge was repeated twice a week for 2 weeks.
Agents Actions37 (1992)
182
Evaluation of lun9 function
Evaluation of airway reactivity
Each guinea pig was placed in a two-chamber plethysmograph system (Pennock Box, Buxco Electronics, Inc.) [2]. SRaw and sG,w were measured. The neck of the guinea pig was extended through a latex collar which sealed the neck opening, establishing two separate plethysmographs. Each plethysmograph was connected to a differential-pressure transducer. Each transducer was connected to a Buxco Electronics preamplifier and oriented such that one port of the transducer ( + ) was attached directly to the plethysmograph, while the other port ( - ) was open to the atmosphere. The head chamber was also connected to a bias flow pump (which provided a constant flow of fresh air) and to a Lovelace nebulizer (In-Tox Products). Nasal air flow was derived from the differential-pressure transducer attached to the head chamber. Thoracic air flow was derived from the differential-pressure transducer attached to the body chamber. A phase comparison between the nasal air flow and the thoracic air flow was used to compute a time delay, from which SRaw and sGaw were computed. The pressure signals from both plethysmographs were electrically differentiated by an on-line noninvasive respiratory analyzer (Buxco Electronics, Inc.), digitized by a data acquisition system (model DA16, Buxco Electronics, Inc.), and monitored by a microcomputer equipped with an ADA board and Buxco Electronics scrolling monitor software.
Baseline values for each animal were established by averaging each lung parameter for 5 min prior to Ach exposure. Ten ml of Ach solution (0.3, 1.0, 3.0, 10.0, or 30.0 mg/ml) was placed into the nebulizer vial and delivered by forcing compressed air at a pressure of 20 psi through the nebulizer for 5 min. The nebulizer was connected by a T piece into each of the neck chambers of two Pennock boxes. Ach challenges were made 3 5 days after the last antigen challenge. The PC,o o (provocation concentration of Ach in mg/ml causing a 100% increase in SRaw) for each animal was determined.
Results
Repeated aeroallergen challenges significantly increased SRawwith concomitant significant decline in sGaw(Table 1). The mean PC100's ofAch (mg/ml) were as follows: before challenge=2.0; after two challenges = 4.5; after four challenges = 7.9. Discussion
The SRaw was significantly increased after repeated aeroallergen challenge in conscious guinea pigs. This may be due to airway inflammation causing smooth muscle depolarization (potassium channel blockade) by threshold concentrations of endogen-
Table 1
Baseline valuesfor sensitizedguineapigs prior to and after repeated antigen challenges Parameters Body weight (g) Peak expiratory flow (ml/sec) Tidal volume(ml) Respiratory rate (breaths/rain) Minute volume(ml/min) Specific airway resistance,SR,w, (cmH20 x s) Specific airway conductance,sG,w, (1/(cmH20 x s))
Before sensitization 384_+20 l 2.8 _+3.0
After two challenges
After four challenges
648 + 14" 15.3-+2.3
706-+21 * 13.9_+1.6 3.18" _+0.28" 99.1 +-7.4 282.3_+23.1
1.92+_0.29
2.87_+0.43
118.0i 10.5 222.9_+36.1
108.3_+7.4 265.3_+28.6
4.6+_0.7
6.0_+0.7
0.59_+0.17
0.29+_0.05b
8.2* •
b
0.19"_+0.03b
Values are averages of 5 min; means+ SEM (N- 10). * P
0065-4299/92/040181-03 $1.50+ 0.20/0 9 1992 Birkhfiuser Verlag, Basel
Repeated aeroallergen challenge induces lung dysfunction but not bronchial hyperresponsiveness in conscious guinea pigs N. Chand 1, K. Nolan, W. Diamantis and R. D. Sofia Wallace Laboratories, Division of Carter-Wallace Inc., Half Acre Rd., Cranbury, NJ 08512, USA
Abstract
Adult male Hartley-strain guinea pigs were sensitized by 10 min exposure to aerosolized 1% ovalbumin (OA; 10 mg/ml in normal saline containing 4% heat-killed B. pertussis vaccine and 0.02% antifoam B emulsion). One week after sensitization, animals were placed in an exposure chamber and challenged (nebulized OA 0.5%) until each animal showed labored breathing. Maximal exposure time was 10 min. Diphenhydramine (20 mg/kg, i.p.) was given 1 h before each OA challenge to protect the animals from bronchospasmic death. Antigen challenge was repeated twice a week for 2 weeks. The specific airway resistance (SRaw) changes in response to increasing concentrations of aerosolized acetyleholine (Ach) were determined. The data obtained in this study demonstrated that repeated antigen challenge produced a significant bronchial tone i.e. an increase in SRaw and a decline in specific airway conductance (SG~w) and failed to induce bronchial hyperreactivity to aerosolized acetylcholine (Ach) in conscious guinea pigs.
Introduction
Bronchial hyperresponsiveness is the main characteristic of asthma. It has been reported that repeated aeroallergen challenge induces airway hyperresponsiveness to aerosolized Ach in actively sensitized, anesthetized guinea pigs [1]. The objective of this study was to produce a model of bronchial hyperresponsiveness by repeated aeroallergen challenge in conscious restrained guinea pigs. Materials and methods
Sensitization procedure Ten male Hartley-strain guinea pigs (CAMM Re1Author for correspondence.
search Laboratory Animals, Wayne, N J) were sensitized by inhalation of an aerosolized 1% ovalbumin solution (OA; 10 mg/ml in normal saline containing 4% heat-killed B. pertussis vaccine and 0.02% antifoam B emulsion, 10 min, 15 psi) [1].
Chronic repeated antigen challenge One week after sensitization, diphenhydramine (20 mg/kg, i.p.) was given 1 h before each challenge to protect the animals from anaphylactic death. Animals were placed in the exposure chamber and exposed to nebulized 0.5% OA solution until each animal exhibited labored breathing and increased respiratory rate. The maximal exposure time was 10 min. Antigen challenge was repeated twice a week for 2 weeks.
Agents Actions37 (1992)
182
Evaluation of lun9 function
Evaluation of airway reactivity
Each guinea pig was placed in a two-chamber plethysmograph system (Pennock Box, Buxco Electronics, Inc.) [2]. SRaw and sG,w were measured. The neck of the guinea pig was extended through a latex collar which sealed the neck opening, establishing two separate plethysmographs. Each plethysmograph was connected to a differential-pressure transducer. Each transducer was connected to a Buxco Electronics preamplifier and oriented such that one port of the transducer ( + ) was attached directly to the plethysmograph, while the other port ( - ) was open to the atmosphere. The head chamber was also connected to a bias flow pump (which provided a constant flow of fresh air) and to a Lovelace nebulizer (In-Tox Products). Nasal air flow was derived from the differential-pressure transducer attached to the head chamber. Thoracic air flow was derived from the differential-pressure transducer attached to the body chamber. A phase comparison between the nasal air flow and the thoracic air flow was used to compute a time delay, from which SRaw and sGaw were computed. The pressure signals from both plethysmographs were electrically differentiated by an on-line noninvasive respiratory analyzer (Buxco Electronics, Inc.), digitized by a data acquisition system (model DA16, Buxco Electronics, Inc.), and monitored by a microcomputer equipped with an ADA board and Buxco Electronics scrolling monitor software.
Baseline values for each animal were established by averaging each lung parameter for 5 min prior to Ach exposure. Ten ml of Ach solution (0.3, 1.0, 3.0, 10.0, or 30.0 mg/ml) was placed into the nebulizer vial and delivered by forcing compressed air at a pressure of 20 psi through the nebulizer for 5 min. The nebulizer was connected by a T piece into each of the neck chambers of two Pennock boxes. Ach challenges were made 3 5 days after the last antigen challenge. The PC,o o (provocation concentration of Ach in mg/ml causing a 100% increase in SRaw) for each animal was determined.
Results
Repeated aeroallergen challenges significantly increased SRawwith concomitant significant decline in sGaw(Table 1). The mean PC100's ofAch (mg/ml) were as follows: before challenge=2.0; after two challenges = 4.5; after four challenges = 7.9. Discussion
The SRaw was significantly increased after repeated aeroallergen challenge in conscious guinea pigs. This may be due to airway inflammation causing smooth muscle depolarization (potassium channel blockade) by threshold concentrations of endogen-
Table 1
Baseline valuesfor sensitizedguineapigs prior to and after repeated antigen challenges Parameters Body weight (g) Peak expiratory flow (ml/sec) Tidal volume(ml) Respiratory rate (breaths/rain) Minute volume(ml/min) Specific airway resistance,SR,w, (cmH20 x s) Specific airway conductance,sG,w, (1/(cmH20 x s))
Before sensitization 384_+20 l 2.8 _+3.0
After two challenges
After four challenges
648 + 14" 15.3-+2.3
706-+21 * 13.9_+1.6 3.18" _+0.28" 99.1 +-7.4 282.3_+23.1
1.92+_0.29
2.87_+0.43
118.0i 10.5 222.9_+36.1
108.3_+7.4 265.3_+28.6
4.6+_0.7
6.0_+0.7
0.59_+0.17
0.29+_0.05b
8.2* •
b
0.19"_+0.03b
Values are averages of 5 min; means+ SEM (N- 10). * P
