Leukaemia inhibitory factor (LIF) upregulates excitatory non-adrenergic non-cholinergic and maintains cholinergic neural function in tracheal explants.

The effect of leukaemia inhibitory factor (LIF) in modulating cholinergic and sensory nerve function was examined using guinea-pig tracheal explants. Specific LIF receptors (LIFR) were immunolocalized to both cholinergic and sensory nerves. Release of SP in culture was not influenced by LIF. Similarly, maximum contraction to carbachol (C(max)) was not influenced by LIF. After 3 h, maximum (E(max)) eNANC-induced contraction in controls was 32+/-2. 5% of C(max). In LIF-treated preparations, E(max) was enhanced to 50+/-4.5% C(max) (P<0.05). Cholinergic nerve-induced contractions after 3 h incubation with LIF were similar to control. After 24 h, control E(max) was 25+/-4.5% C(max) (58% smaller than E(max) at 3 h). In contrast, in LIF-treated preparations, E(max) was 37+/-2.5% C(max), (24% smaller than at 3 h, P<0.05). This did not appear to be due to the effect of LIF on muscarinic M(2) receptor expression or function. Thus LIF appears to differentially influence the function of airway nerves and thus may provide an important link between the immune and neural systems.

Detection of endothelin receptors in rat and guinea-pig airway nerves by immunohistochemistry.

We investigated the existence of endothelin (ET) receptor subtypes in airway neurones from the rat and guinea-pig and determined the ability of these receptors to modulate contractile function. Rat tracheal neuron cultures as well as rat and guinea-pig whole mount preparations were labelled with antibodies to the cholinergic nerve marker choline acetyltransferase (ChAT), the neuron specific marker protein gene product 9.5 (PGP 9.5) and to ET(A)and ET(B)receptors. Following incubation with fluorescent secondary antibodies, fluorescence was detected using confocal microscopy with dual emission protocols. Specific fluorescence was detected both in whole mount preparations and neuron cultures, in association with the primary antibodies. Specific fluorescence associated with either ET(A)and ET(B)receptors was colocalized with that for PGP 9.5. Despite the presence of ET(A)and ET(B)receptors on airway nerves, ET-1 failed to significantly alter cholinergic, excitatory or inhibitory non-adrenergic-non-cholinergic nerve-mediated responses in guinea-pig airways. This is in sharp contrast to ET-1-induced potentiation of responses to cholinergic nerve-evoked contraction in rat trachea. Thus, although ET(A)and ET(B)receptors exist in airway cholinergic neurons in whole mount preparations and in primary neuron cultures from rat and guinea-pig trachea, the influence of these receptors on contractile function appears to be species-dependent.

Distribution of immunoreactive endothelin in the lungs of mice during respiratory viral infection.

Respiratory tract viral infections are associated with the generation of a wide array of pro-inflammatory cytokines, some of which enhance the release of the potent airway smooth muscle spasmogen, endothelin, from respiratory epithelial cells in tissue culture. The aim of this study was to determine whether the content and distribution of immunoreactive endothelin in the intact murine lung is increased during the course of a respiratory tract viral infection. Mice were inoculated intranasally with Influenza A/PR-8/34 virus or sterile vehicle and at various days postinoculation were sacrificed, and their lungs processed for either fluorescence immunohistochemistry with rabbit anti-endothelin sera or measurement of immunoreactive endothelin with an enzyme-linked immunosorbent assay (ELISA). At 2 and 4 days postinoculation, the content of immunoreactive endothelin in lung extracts of virus-infected mice was approximately twice that present in lung extracts from control mice (n=3-4, p<0.05). Consistent with this, an increased intensity and broader distribution of fluorescent immunohistochemical staining for endothelin was observed in the airway epithelium of the trachea and intrapulmonary airways of virus-infected mice. This study has clearly demonstrated that respiratory tract viral infection is associated with an increased content and broader distribution of immunoreactive endothelin within the lungs of mice. Whether the elevated content of endothelin contributes to the symptoms of virus-induced hyperresponsiveness or to virus-induced exacerbations of asthma remains to be established.

Immunocytochemical detection of endothelin receptors in rat cultured airway nerves.

Endothelin-1 (ET-1) has been shown to potentiate cholinergic neurotransmission in human bronchus as well as in airways from a variety of animal species, suggesting that ET receptors exist prejunctionally on airway cholinergic nerves. We have successfully isolated and maintained rat tracheal para-sympathetic neurons in culture. Most cultured cells were associated with specific fluorescence for the nerve cell marker protein gene product 9.5 (PGP 9.5). These cultures contained a high proportion of parasympathetic neurons. Importantly, specific immunofluorescent antibodies for ETB receptors were colocalized with those for PGP 9.5. Therefore, for the first time, ETB receptors have been shown to exist on airway parasympathetic neurons in culture.