Effect of nedocromil sodium on allergen-, PAF-, histamine- and bradykinin-induced airways vasodilatation and pulmonary obstruction in the pig

The roles of the prostaglandin D(2) receptors DP(1) and CRTH2 in promoting allergic responses

Prostaglandin D(2) (PGD(2)) is produced by mast cells, Th2 lymphocytes and dendritic cells and has been detected in high concentrations at sites of allergic inflammation. PGD(2) exerts its inflammatory effects through high affinity interactions with the G protein coupled receptors DP(1) and chemoattractant-homologous receptor expressed on Th2 cells (CRTH2, also known as DP(2)). DP(1) and CRTH2 act in concert to promote a number of biological effects associated with the development and maintenance of the allergic response. During the process of allergen sensitization, DP(1) activation may enhance polarization of Th0 cells to Th2 cells by inhibiting production of interleukin 12 by dendritic cells. Upon exposure to allergen in sensitized individuals, activation of DP(1) may contribute to the long lasting blood flow changes in the target organ. CRTH2 is expressed by Th2 lymphocytes, eosinophils and basophils and may mediate the recruitment of these cell types during the late phase allergic response. The role played by CRTH2 in promoting the production of Th2 cytokines and IgE make antagonism of this receptor a particularly attractive approach to the treatment of chronic allergic disease.

Deep-breath frequency in bronchoconstricted monkeys (Macaca fascicularis)

Deep-breath frequency has been shown to increase in spontaneously obstructed asthmatic subjects. Furthermore, deep breaths are known to be regulated by lung rapidly adapting receptors, yet the mechanism by which these receptors are stimulated is unclear. This study tested the hypothesis that deep-breath frequency increases during experimentally induced bronchoconstriction, and the magnitude of the increased deep-breath frequency is dependent on the method by which bronchoconstriction is induced. Nine cynomolgus monkeys (Macaca fascicularis) were challenged with methacholine (MCh), Ascaris suum (AS), histamine, or an external mechanical resistance. Baseline (BL) and challenge deep-breath frequency were calculated from the number of deep breaths per trial period. Airway resistance (Raw) and tissue compliance (Cti), as well as tidal volume, respiratory rate, and minute ventilation, were analyzed for BL and challenged conditions. Transfer impedance measurements were fit with the DuBois model to determine the respiratory parameters (Raw and Cti). The flow at the airway opening was measured and analyzed on a breath-by-breath basis to obtain the ventilatory parameters (tidal volume, respiratory rate, and minute ventilation). Deep-breath frequency resulting from AS and histamine challenges [0.370 (SD 0.186) and 0.467 breaths/min (SD 0.216), respectively] was significantly increased compared with BL, MCh, or external resistance challenges [0.61 (SD 0.046), 0.156 (SD 0.173), and 0.117 breaths/min (SD 0.082), respectively]. MCh and external resistance challenges resulted in insignificant changes in deep-breath frequency compared with BL. All four modalities produced similar levels of bronchoconstriction, as assessed through changes in Raw and Cti, and had similar effects on the ventilatory parameters except that non-deep-breath tidal volume was decreased in AS and histamine. We propose that increased deep-breath frequency during AS and histamine challenge is the result of increased vascular permeability, which acts to increase rapidly adapting receptor activity.

Species differences in bradykinin receptor-mediated responses of the airways

1. Bradykinin (BK) is a nine amino acid peptide (Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg) formed from the plasma precursor kininogen during inflammation and tissue injury. The actions of BK are mediated by G protein-coupled cell surface receptors, designated B1 and B2. 2. BK has a plethora of effects in the airways including bronchoconstriction, bronchodilation, stimulation of cholinergic and sensory nerves, mucus secretion, cough and oedema resulting from promotion of microvascular leakage. These airway effects are mediated in the main by the B2 receptor subtype. 3. BK acts mainly indirectly, primarily through airway nerve activation, but also by the release of prostanoids, thromboxanes and nitric oxide (NO). 4. Airway responses to BK have been studied in detail in guinea-pigs, mice, sheep and rats. This review describes the effects of BK in these species and draws comparison with its effects in normal humans and patients with respiratory diseases. 5. Despite its many and varied effects in the airways of animals and man, the exact contribution of BK to airways disease remains unclear.

Bronchial responsiveness to inhaled metabisulfite in asthmatic children increases with age

Inhaled bisulfite (HSO3) aerosol produces bronchoconstriction in asthmatics but not in normals. This effect is probably due to local formation of SO2 which stimulates vagal afferents in the airway mucosa, and gives rise to bronchoconstriction that is partly due to a cholinergic reflex. Metabisulfite (MBS) produces bronchoconstriction in most adult asthmatics, but its effect in children has received little attention. The present study was done to assess MBS-induced bronchoconstriction as a function of age in asthmatic children, and to compare MBS responsiveness with the response to inhaled metacholine (MCH), which is commonly used for bronchoprovocation testing. In 36 children with moderate asthma, selected to cover the age range between 3 and 20 years, we compared airway responsiveness to MBS and MCH, expressed as the provocative dose that causes a 20% fall in baseline forced expiratory volume in 1 sec (FEV1, PD20). We also measured the PD20 to MBS after pretreatment with the anticholinergic ipratropiumbromide, to estimate the noncholinergic component of the response. After bronchial provocation with MCH, a PD20 was reached in 32 children, and no significant relation of PD20 to age was found. A PD20[MBS] was seen in only 17 patients, and more frequently in older children. There was a significant negative correlation between age and PD20[MBS]. Ipratropium pretreatment reduced the response to MBS in 14 of the 17 children who had a PD20[MBS]. The PD20[MBS] after ipratropium pretreatment was also significantly negatively related with age. This suggested that the increased prevalence of MBS responsiveness was due to an increase of the noncholinergic component of the response.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for a distinct H7-resistant form of protein kinase C in rat anterior pituitary gland

Inhibition of phorbol 12,13-dibutyrate-induced protein kinase C (PKC) activity from rat midbrain, anterior pituitary and a number of other tissues, as well as COS 7 cells, was studied in vitro. In anterior pituitary, Ca(2+)-independent activity was notably resistant to H7 but sensitive to staurosporine and Ro 31-8220. All Ca(2+)-dependent activity was sensitive to these three inhibitors. Mezerein and 1,2-dioctanoyl-sn-glycerol also activated this H7-insensitive PKC from anterior pituitary. The distribution of this activity, prominently expressed in pituitary and perhaps also lung, and its characteristic resistance to H7 but not other inhibitors, does not obviously correlate with that of any of the well-characterised PKCs, and may reflect either a novel or a modified isoform.

The possible role of prostaglandin D2 in the long-lasting airways vasodilatation induced by allergen in the sensitized pig

Allergen-induced nasal and bronchial vasodilatation and bronchoconstriction were studied in ascaris-sensitized pigs with and without pretreatment with diclofenac sodium, to evaluate the contribution of prostanoids in these responses. The bronchoconstriction induced by allergen aerosol challenge was enhanced by diclofenac, whereas the duration of the bronchial vasodilatation was reduced from 80 to 30 min, without changing the maximal effect. However, both the maximal effect and the duration of the nasal vasodilatation were reduced upon nasal allergen challenge by 60% (P less than 0.01) and from 72 to 16 min (P less than 0.05), respectively. Bronchial challenge with the allergen also induced nasal vasodilatation of long duration and this response was highly sensitive to diclofenac pretreatment. I.v. injections of prostaglandins (PG) E1, E2, I2 and D2 revealed that only PGD2 induced vasodilatation of long duration in the airways without major effects on the systemic arterial blood pressure. Nebulization of PGD2 (0.7-1.4 mumol) into the pig airways also induced marked vasodilatation of long duration (greater than or equal to 40 min), especially in the nasal circulation. The vasodilatory responses to PGD2 were not changed by systemic pretreatment with capsaicin or diclofenac. Challenge in the airways with platelet-activating factor (PAF) produced bronchial and vascular responses similar to those seen with the allergen and the vasodilatory responses to PAF were partly sensitive to diclofenac. We propose that a long-lasting component of the allergen-induced vasodilatation in the pig airways, especially in the nasal mucosa, may be caused by the release of PGD2, acting independently of sensory nerves. Allergen and PAF aerosol challenge in the lung may also induce the release of a vasodilatory prostaglandin, possibly PGD2 into the systemic circulation, thereby inducing nasal vasodilatation.