Effect of beta 2-adrenoceptor agonists against platelet-activating factor-induced airway microvascular leakage and bronchoconstriction in the guinea pig

The indirect effect of Tityus discrepans on rabbit pulmonary vasculature

Serum (IS) was obtained 0.5, 2, 4 or 6 h after inoculating s.c. six rabbits (approximately 2 kg) in each time period with 1 mg/kg of Tityus discrepans (Td) venom; the control was serum obtained from four rabbits 4 h after injecting them 1 ml s.c. of 0.9% NaCl. IS produced a transient (<25 min) rise in pulmonary artery pressure of isolated and perfused rabbit lungs, other lung parameters were not altered. We found that both scorpion venom and IS produced a approximately 50% transient increase of transendothelial electric resistance in cultured tissue human umbilical cord vein. Neither venom nor IS changed the transepithelial electrical resistance of tissue cultured human airway epithelia. The experiments suggest that humoral factors contained in the inoculated serum modify vascular endothelium in a much more effective manner than the venom by itself. These experiments also make it unlikely that vascular endothelium is the source of the humoral factors contained in inflammatory serum.

Effect of dopamine on platelet activating factor induced-pulmonary edema in isolated and perfused rabbit lungs

The effect of dopamine over pulmonary edema induced by PAF was studied. Thirty preparations of rabbit lungs were used: six control preparations (CP), six PAF preparations (PP) in which we injected a dose of 1 microg/kg of rabbit weight and eighteen dopamine preparations (DAP) divided in three groups of six pretreated with a dose of 1-5 (dopaminergic range), 10-20 (Beta range) and 20-30 ug/kg/min (Alpha range) of dopamine, respectively for 30 min, followed by an injection of PAF as in the PP. DAP at Beta and Alpha-adrenergic range decreased pulmonary artery pressure (Pap) as compared to CP, with values of 11.66 (CI 95%: 10.83-12.48), 11.66 (CI 95%: 9.87-13.44) versus 17.12 (CI 95%: 16.12-18.11) cm of water, respectively. DAP in Beta and Alpha-adrenergic range prevented Pap increment as compared to PP, with values of 17.16 (CI 95%: 16.37-17.94), 17.5 (CI 95%: 14.93-20.06) versus 84 cm of water (CI 95%: 71.41-96.58), respectively. Dopamine, at its three ranges inhibited the augmentation of the fluid filtration rate observed in PP with values of 1.01 (CI 95%: 0.77-1.24), 0.03 (CI 95%: 0.01-0.04) and 0.02 g/min (CI 95%: -0.0004-0.03) versus 2.13 g/min (CI 95%: 1.56-2.69), respectively. We concluded that dopamine has a vasodilator effect on Pap and exerts an inhibiting action over PAF effects in pulmonary circulation. Such effects seem to be mainly mediated by Beta-receptors, rather than by dopaminergic receptors.

Effects of inhaled glaucine on pulmonary responses to antigen in sensitized guinea pigs

The alkaloid (S)-(+)-1,2,9,10-tetramethoxyaporphine (glaucine) is a phosphodiesterase 4 inhibitor with bronchodilator and anti-inflammatory activity in vitro. In this study, we examined the in vivo effects of glaucine on an animal model of asthma. In ovalbumin sensitized guinea pigs, inhaled glaucine (10 mg ml(-1), 3 min) inhibited the acute bronchoconstriction produced by aerosol antigen (antigen response was 256+/-42 and 95+/-14 cm H(2)O l(-1) s(-1) in control and glaucine-treated animals, respectively; P<0.05). Pretreatment with glaucine (10 mg ml(-1), 10 min inhalation, 30 min pre- and 3 h post-antigen exposure) markedly reduced airway hyperreactivity to histamine, eosinophil lung accumulation, and increased eosinophil peroxidase activity in bronchoalveolar lavage fluid 24 h after exposure of conscious guinea pigs to aerosol antigen. In addition, inhaled glaucine (5-10 mg ml(-1), 3 min) inhibited the microvascular leakage produced after inhaled antigen at all airway levels. These data support the potential interest of phosphodiesterase 4 inhibitors in asthma treatment.

Effect of Fenoterol on PAF-induced lung edema in isolated and perfused rabbit lungs

We have studied the effects of fenoterol on PAF-induced response in pulmonary circulation. We used 28 isolated and perfused rabbit lungs preparations: eight control preparations (CP), four vehicles preparations (VP), eight PAF preparations (PP) with two doses of PAF, one called low dose (LD = 0.5 microg/kg of weight) and the other high dose (HD = 1 microg/kg of weight) and eight Fenoterol preparations (FP) which we administered 0.05 mg of Fenoterol for 15 min, followed by a LD and HD of PAF. FP prevented elevation of pulmonary artery pressure (Ppa) as compared to PP, at LD of PAF: 12.615 (CI 95%: 8.57-20.885) versus 83.705 (CI 95%: 50.55-114.3) cm of water; and at HD of PAF: 19.38 (CI 95%: 11.235-28.94) versus 205.1 (CI 95%: 141.3-271) cm of water respectively. FP prevented the increase in fluid filtration rate (FFR) observed in PP at both doses of PAF LD: 0.765 (CI 95%: 0.07-3.385) versus 0.01 (CI 95%: -0.05-0.005) g/min; HD: 5.515 (CI 95%: 2.425-8.865) versus 0.03 (CI 95%: 0-0.33) g/min. Our results suggest that PAF has a vasoconstrictor effect that produces lung edema and this effect is inhibited by fenoterol.

Effect of beta 2-agonists on histamine-induced airway microvascular leakage in ozone-exposed guinea pigs

beta 2-adrenergic agonists exhibit antipermeability effects in the airways. However, it is not known whether beta 2-agonists have this beneficial effect in airway mucosa that is already inflamed. We evaluated the effects of two inhaled beta 2-agonists, salbutamol and formoterol, on the histamine-induced bronchoconstriction and plasma extravasation in the airways of guinea pigs with or without ozone exposure. Total pulmonary resistance (RL) was measured before and after histamine inhalation in anesthetized animals that were pretreated with inhaled salbutamol, formoterol, or saline. Plasma extravasation in the airways was measured using Evans blue dye. In the control animals not exposed to ozone, salbutamol and formoterol each significantly reduced both the histamine-induced bronchoconstriction and the plasma extravasation in the trachea and main bronchi. In the ozone-exposed animals, the increase in RL after histamine was greater than that in control animals. Salbutamol and formoterol each significantly reduced histamine-induced bronchoconstriction, even in the ozone-exposed animals. Salbutamol did not affect the histamine-induced plasma extravasation, whereas formoterol reduced the plasma extravasation in the main bronchi, but not in the trachea, of the animals exposed to ozone. These results suggest that the anti-inflammatory properties of formoterol in inflamed airways may contribute to the beneficial effects in the treatment of airway inflammation.

Inhibition of PAF-induced gas exchange defects by beta-adrenergic agonists in mild asthma is not due to bronchodilation

Salbutamol inhibits neutropenia, increased airway resistance, and gas exchange abnormalities provoked by platelet-activating factor (PAF) challenge in normal persons. To further explore the intriguing dissociation between spirometric abnormalities and gas exchange defects shown in patients with asthma, we investigated whether the salbutamol-induced improvement in gas exchange disturbances after PAF is the result of bronchodilation by comparing this effect with that of ipratropium bromide. We hypothesized that ipratropium bromide, an anticholinergic agent without vascular effects, should block PAF-induced bronchoconstriction but not interfere with its systemic, neutropenic, and gas exchange effects. We studied eight nonsmokers with mild asthma (26 +/- 2.0 SE yr of age) who, prior to PAF challenge (18 micrograms), inhaled either ipratropium bromide (80 micrograms) or salbutamol (300 micrograms) in a randomized, double-blind, crossover fashion 1 wk apart. Peripheral blood neutrophils, respiratory system resistance (Rrs), arterial blood gases and ventilation-perfusion (VA/Q) inequalities were measured 5, 15, and 45 min after PAF. Compared with pretreatment with salbutamol, ipratropium bromide also blocked the increase of respiratory system resistance (Rrs) but did not prevent facial flushing and neutropenia (p < 0.03) at 5 min nor the decrease of PaO2 (p = 0.08 and 0.05), the increase of AaPO2 (p < 0.02 each), and the deterioration of VA/Q relationships (p < 0.05 each) at 5 and 15 min, respectively. This functional pattern was similar to that observed previously in normal subjects and in nonpremedicated asthmatic patients after PAF, with return to baseline values at 45 min. By contrast, salbutamol blocked PAF-induced increased Rrs, in addition to all the other PAF-induced abnormalities. These findings indicate that, in patients with mild asthma, salbutamol inhibits PAF-induced neutropenia and gas exchange abnormalities by mechanisms involving other than airway smooth muscle narrowing, possibly by acting on both the bronchial and pulmonary circulations.

Effects of selective phosphodiesterase inhibitors on platelet-activating factor- and antigen-induced airway hyperreactivity, eosinophil accumulation, and microvascular leakage in guinea pigs

There is currently interest in the potential use of selective inhibitors of cyclic nucleotide phosphodiesterases (PDE) in the treatment of asthma. In this study we examined the effects of three selective PDE inhibitors, milrinone (PDE III), rolipram (PDE IV) and zaprinast (PDE V), on the broncoconstriction produced by antigen and histamine, the airway hyperreactivity and microvascular leakage after aerosol exposure to platelet-activating factor (PAF) and antigen, and the antigen-induced eosinophil infiltration in guinea-pig lung. Inhaled rolipram (0.01-10 mg ml-1) inhibited dose dependently the bronchospasm produced by aerosol antigen (5 mg ml-1) an anaesthetised, ventilated guinea-pigs. Rolipram (10 mg ml-1) produced maximal inhibition of antigen-induced bronchoconstriction but only partial inhibition of the response to aerosol histamine (1 mg ml-1). Milrinone and zaprinast (each 10 mg ml-1) showed weak, or no, inhibitory effects against bronchoconstriction produced by aerosol antigen or histamine. Pretreatment with rolipram (10 mg kg-1, i.p.) prevented airway hyperreactivity to histamine which develops 24 h after exposure of conscious guinea-pigs to aerosol PAF (500 micrograms ml-1) or antigen (5 mg ml-1). The pulmonary eosinophil infiltration obtained with 24 h of antigen-exposure was inhibited by rolipram. In contrast, milrinone and zaprinast (each 10 mg kg-1, i.p.) failed to reduce either the airway hyperreactivity of the eosinophil accumulation in these animals. Rolipram (1-10 mg ml-1) reduced the extravasation of Evans blue after aerosol PAF (500 micrograms ml-1) at all airway levels while a lower dose (0.1 mg ml-1) was only effective at intrapulmonary airways. Rolipram (0.01-1 mg ml-1) markedly reduced airway extravasation produced by inhaled antigen (5 mg ml-1). Zaprinast (1-10 mg ml-1) was also effective against airway microvascular leakage produced by aerosol PAF or antigen while milrinone (10 mg ml-1) had no antiexudative effect. These data support previous suggestions that pharmacological inhibition of PDE IV results in anti-spasmogenic and anti-inflammatory effects in the airways and may be useful in the treatment of asthma.