Effects of inhaled bradykinin in conscious guinea-pigs

Alan Blair1, William R Ford1, Joachim J Bugert2, Kenneth J Broadley1

1Welsh School of Pharmacy, Cardiff University, Cardiff, UK, 2Welsh College of Medicine, Cardiff University, Cardiff, UK

Increased levels of tissue kallikrein and kinins are found in the bronchoalveolar fluid of asthmatics after allergen challenge (Christiansen et al 1992) and inhalation of bradykinin (BK) causes bronchoconstriction in asthmatics, but not in non-asthmatics (Fuller et al 1987). In the lung, BK is thought to act mainly on BK B2 receptors and is broken down by neutral endopeptidase (NEP) and angiotensin converting enzyme (ACE). We examined airway function and inflammatory cell influx to the lungs after inhaled BK in conscious guinea-pigs.

Lung function was measured as specific airway conductance (sGaw) in conscious male Dunkin-Hartley guinea pigs (300-400g, n=6) by whole body plethysmography. Lung function was recorded before and at 0, 5 and 10min after a 0.1, 0.3 or 1mM nose only 20, 40 or 60s BK exposure. The ACE inhibitor captopril (i.p. 1mg/kg) and the NEP inhibitor phosphoramidon (i.p. 0.1mg/kg or 10mM by inhalation 20 minutes before) were given 1h before BK exposure. 30min after BK exposure, the animals were killed by sodium pentobarbital overdose and bronchoalveolar lavage (BAL) performed for total and differential cell counts. Some animals were sensitized with ovalbumin (OA) (i.p. 0.1mg) on days 1 and 5 and then given OA (0.01%) by aerosol on day 15. The animals received BK (20s, 1mM) 24h before and 24h after OA exposure to test for airway hyperreactivity (AHR). Comparisons were made by Students t-test with P<0.05 considered significant.

In untreated non-sensitised animals there was no significant decrease in sGaw after BK exposure up to 1mM. After captopril, inhaled BK at 1mM for 20sec caused a significant fall in sGaw (22.4 ± 6.3%) indicating bronchoconstriction, but not at 0.1 or 0.3mM. However, after captopril, BK at 0.3mM for 60 but not 40s caused a significant decrease in sGaw (17.9±6.4%). After phosphoramidon (0.1mg/kg i.p.) there was no change in sGaw after 1mM BK exposure, but after aerosolised exposure (10mM) there was a significant decrease (21.7 ± 4.4%). In animals treated with inhaled phosphoramidon (10mM) and captopril (1mg/ml, i.p.) the decrease in sGaw (22.3±3.25%) was no greater than after individual treatments. In OA sensitized and challenged guinea-pigs, BK (1mM) significantly reduced sGaw (18.1 ± 2.2%) compared to before OA, indicating AHR. In naïve animals the cell counts (×106) in the BAL fluid were: total cells 1.95 ± 0.09, macrophages 1.68 ± 0.09, eosinophils 0.2 ± 0.04, neutrophils 0.04 ± 0.03 and lymphocytes 0.03 ± 0.01. In animals receiving captopril and BK (1mM) there was no significant difference in any cell type but after phosphoramidon (100mM inhalation) and captopril there were significant increases in total cells (3.15 ± 0.26), macrophages (2.63 ± 0.24) and eosinophils (0.4 ± 0.06).

The failure of BK exposure up to 1mM in non-sensitized guinea-pigs to produce bronchoconstriction and cell influx may be due to its rapid breakdown as inhibitors of ACE and NEP allowed BK to produce a significant bronchoconstriction and cell influx. Bronchoconstriction to inhaled BK after OA sensitisation and challenge indicated airway hyperreactivity analogous to the situation in asthmatics.

Christiansen et al (1992) Am Rev Respir Dis 145: 900-905

Fuller et al (1987) Am Rev Respir Dis 135: 176-180