Reflex decrease of histamine-induced bronchoconstriction after laryngeal stimulation in asthmatic patients

Neurotrophins and neurotrophin receptors in allergic asthma

The neurotrophins nerve growth factor, brain-derived neurotrophic factor, neurotrophin-3 (NT-3) and NT-4 play a pivotal role in the development of the nervous system. Despite their well-known effects on neurons, elevated neurotrophin concentrations have been observed under pathological conditions in sera of patients with inflammatory disorders. Patients with asthma feature both airway inflammation and an abnormal airway reactivity to many unspecific stimuli, referred to as airway hyperresponsiveness, which is, at least partly, neuronally controlled. Interestingly, these patients show increased levels of neurotrophins in the blood as well as locally in the lung. It has been demonstrated that neurotrophin release from immune cells is triggered by allergen contact. The presence of neurotrophins and the neurotrophin receptors p75 (p75NTR), tyrosine kinase A (TrkA), TrkB and TrkC have been described in several immune cells. There is strong evidence for an involvement of neurotrophins in regulation of hematopoiesis and, in addition, in modulation of immune cell function in mature cells circulating in blood or resting in lymphatic organs and peripheral tissues. The aim of this review is to demonstrate possible roles of neurotrophins during an allergic reaction in consideration of the temporospatial compartimentalization.

Vasoactive intestinal polypeptide as mediator of asthma

Vasoactive intestinal polypeptide (VIP) is one of the most abundant, biologically active peptides found in the human lung. VIP is a likely neurotransmitter or neuromodulator of the inhibitory non-adrenergic non-cholinergic airway nervous system and influences many aspects of pulmonary biology. In human airways VIP-immunoreactive nerve fibres are present in the tracheobronchial airway smooth muscle layer, the walls of pulmonary and bronchial vessels and around submucosal glands. Next to its prominent bronchodilatory effects, VIP potently relaxes pulmonary vessels. The precise role of VIP in the pathogenesis of asthma is still uncertain. Although a therapy using the strong bronchodilatory effects of VIP would offer potential benefits, the rapid inactivation of the peptide by airway peptidases has prevented effective VIP-based drugs so far and non-peptide VIP-agonists did not reach clinical use.

Non-adrenergic, non-cholinergic function in the human airway

Alterations in non-adrenergic, non-cholinergic (NANC) function may contribute to nocturnal asthma. We have attempted to clarify the importance of the NANC system in the circadian variation in airway calibre in mild asthmatics and nocturnal asthmatics. NANC function in the human airway was studied at 0400 and 1600 hours in 12 nocturnal asthmatics and 12 mild asthmatics by measuring oscillatory resistance (Ros) following capsaicin inhalation. Measurements were made after combined beta- and atropinic blockade in the mild asthmatics but after atropinic blockade alone in the nocturnal asthmatics, in whom beta-blockade is contraindicated. To determine whether beta-blockade influences NANC bronchodilatation, we also studied 12 normal subjects with and without beta-blockade at 1600 hours only. The mild asthmatics showed differing (P = 0.007) resistance changes 1-3 min after capsaicin at 1600 hours (fall in Ros + 1%, CI -2% to 3%) from that at 0400 hours (-4%, CI -8% to -1%) but the nocturnal asthmatics showed no significant difference in response to capsaicin at the two times (fall in Ros: 1600 hours -9%, CI -15% to -3%; 0400 hours -3%, -7% to 1%). The normal subjects showed greater (P = 0.0001) bronchodilatation 1-3 min after capsaicin following atropine plus propranolol (-7%, -11% to -3%) than after atropine alone (-2%, -6% to 2%), supporting interaction between the beta-sympathetic and NANC systems in the human airway, NANC bronchodilatation being inhibited by beta-sympathetic activity. Our observations confirm circadian variation in NANC function in mild asthmatics and suggest interaction between the beta-adrenergic and the NANC bronchodilating system in the normal human airway.

Decrease in the airways' nonadrenergic noncholinergic inhibitory system in allergen sensitized rabbits

A decrease in the airways' nonadrenergic noncholinergic inhibitory (NANC-i) system is one of the mechanisms that may contribute to allergen-induced changes in neural control within airways. We measured the airways' neurally mediated contractile and relaxant (NANC-i) responses in tracheal segments and left mainstem bronchus (LMB) from normal (control), immune (ragweed sensitized), and immune challenged rabbits. Immune rabbits were sensitized to mixed ragweed extract through parenteral injections from birth, while the immune challenged group had an additional airway exposure to aerosolized ragweed 48 hours prior to the in vitro studies. Neurally mediated contractile responses to electrical field stimulation (EFS) were increased in the immune challenged group, with the increase most significant in tracheal smooth muscle at a stimulation frequency of 20 Hz. To assess NANC-i responses, airway smooth muscle (ASM) segments from these groups were placed in tissue baths containing atropine (10(-6) M) and propranolol (5 x 10(-6) M). After contraction of the tissue with neurokinin A (NKA, 10(-5) M), the NANC-i response to EFS at 20 Hz was measured and reported as the mean (+/- SEM) percent relaxation. No significant differences were seen in the contractile responses of ASM segments to NKA among the three groups. The tracheal segments showed a significantly different NANC-i relaxation response among all groups: in the control group, 29.1 +/- 3.7; in the immune group 15.8 +/- 2.3%; and in the immune challenged group, 2.1 +/- 4.2%.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of passive sensitization on the mechanical activity of human isolated bronchial smooth muscle induced by substance P, neurokinin A and VIP

1. The effect of passive sensitization on the mechanical activity of human isolated bronchial smooth muscle induced by the following neuropeptides substance P (SP), neurokinin A (NKA) and vasoactive intestinal peptide (VIP) was studied both in the absence and in the presence of the neutral endopeptidase (NEP) inhibitor, phosphoramidon. 2. Cumulative concentration-response curves (CCRC) to these neuropeptides were constructed in human passively sensitized isolated bronchial rings and compared to those in paired controls. Passively sensitized human isolated bronchial rings were tissues incubated overnight in serum from asthmatic patients atopic to Dermatophagoides pteronyssinus and paired controls were tissues originating from the same lung specimens but incubated overnight in serum from healthy donors. 3. In the absence of phosphoramidon, passive sensitization significantly increased the amplitude of the contractile responses to SP and NKA including that to the maximal concentration given from 50 +/- 5% to 76 +/- 6% (n = 5, P < 0.05) and from 70 +/- 7% to 101 +/- 6% (n = 5, P < 0.05) of the maximal response to acetylcholine, respectively. Passive sensitization significantly shifted to the left the CCRC for both tachykinins as measured by the geometric means dose-ratios which were 8.5 (95% confidence limits (CL): 3.1-13.9) and 7.3 (95% CL: 4.2-10.3) for SP and NKA, respectively. 4. In the presence of phosphoramidon (10 microM), passive sensitization still increased significantly the amplitude of the contractile responses to SP and NKA including that to the maximal concentration given from 74 +/- 4% to 115 +/- 7% (n = 5, P<0.05) and from 104 +/- 9% to 146 +/- 16% (n = 5, P<0.05)of the maximal response to acetylcholine, respectively. Passive sensitization still significantly shifted to the left the CCRC for both tachykinins as measured by the dose-ratios which were 9.0 (95% CL:4.3-13.6) and 5.4 (95% CL: 2.9-7.9) for SP and NKA, respectively.5. The relaxant response to the maximal concentration of VIP given in tissues precontracted with histamine (0.5 mM) was significantly reduced by passive sensitization from 41 +/- 4% to 25 +/- 3% (n = 5,P <0.05) of the amplitude of the precontraction in the absence of phosphoramidon and from 72 +/- 1%to 49 +/- 4% (n = 5, P<0.05) in the presence of phosphoramidon (10 microM). Passive sensitization significantly shifted to the right the CCRC for VIP as measured by the dose-ratios which were 10.4(95% CL: 6.6-14.1) and 6.4 (95% CL: 3.0-9.8) in the absence and in the presence of phosphoramidon,respectively.6. We conclude that passive sensitization enhances the mechanical response to neuropeptides which contract human isolated bronchial smooth muscle and reduces that to a neuropeptide which relaxes it.The mechanism of passive sensitization-induced changes in the mechanical activity appears to be independent of a decrease in NEP activity since these changes persist in the presence of the NEP inhibitor, phosphoramidon.