| Aims and Meaning: Bronchial asthma (asthma) is one of the diseases which are harmful to human health, and results of epidemiologic surveies show that the morbility and mortality of asthma is increasing all over the world. Nowadays most people consider the etiopathogenisis and nosogenesis of asthma is the result of interaction between genetic gene and environment. The environmental agents include inhalter, infection, food and some medicine. Recently some studies have found that the morbility of asthma increases after virus infection, and most adults are infected by rhinovirus while most children are infected by RSV. After further studying, people find that simple RSV infection couldn't directly induce asthma, but asthma could emerge after getting in touch with allergen following RSV infection. So the aim of our study is trying to reveal the neuromechanism of RSV-induced asthma in asthmatic models which are built by RSV infection and OVA inhalation in guinea pigs.Methods:①Respiratory syncytial virus was cultured on Hep-2 cells, and we chose the RSV with proper toxicity by cytopathic effect and TCID50 test to infect guinea pigs. Female healthy guinea pigs (n=50) were randomly divided into 6 groups: Hep-2 group (n=9), RSV group (n=9), Hep-2/NS group (n=8), RSV/NS group (n=8), Hep-2/OVA group (n=8) and RSV/OVA group (n=8). Hep-2 and RSV(TCID50=5×10-5.5) were given in the form of nose drops and NS (normal saline) and OVA (ovalbumin) were inspired in gas. All animals were inoculated again in the same way on day 2.②On day 7 we tested the airway responsiveness by electrophysiolograph and electrical stimulation of vagus nerves in guinea pigs, then recorded and analyzed the results of intra-airway pressure between two groups. All animals were intravenously gave selective M2 receptor excitomotor pilocarpine in the dose of 0.1,1,10 and 100μg/kg , then we tested IPs of the two groups and assessed the function of prejunctional inhibited M2 receptor on the airway parasympathetic nerves. We did bronchovesicular lavage with 10 mL normal saline, then collected all cells in BALF, stained cells by Giemsa's stain and counted the total number of cells and differential cells numbers for observing the inflammatory changes in lungs after RSV infection. We chose the Hep-2 group as control group.③On day 7, guinea pigs from Hep-2/NS group, RSV/NS group, Hep-2/OVA group and RSV/OVA group were inhaled with 1% OVA or NS, 30 min per time, once two-day and lasted for two weeks to build asthmatic models. We tested whether the models were successful by HE staining and total cells and eosinophils counting in tracheal mucosa and submucosa.④On day 21, we measured the airway responsiveness and M2 receptor function in the same way discripted above and analyzed the results, and counted the number of positive cholinergic fibers in smooth muscle by immunochemistry. We chose the Hep-2/NS group as control group. Results:①Without electrical stimulation of the vagus nerves, the IPs of the two groups were: 11.08±1.02,11.75±1.47, which had no significant difference (P>0.05). After stimulation, IPs of the two groups both increased according to stimulating frequency, but the IP of the RSV group was higher than that of controls (P<0.05). After giving pilocarpine, IP of controls decreased according to the doses of pilocarpine, while the extent of decrease of RSV group was much less than that of controls, which had significant difference (P<0.05). And the numbers of total cells, mononuclear cell, neutrophils and eosinophils of RSV group were much higher than those of Hep-2 group, which had significant difference (all P<0.01).②On day 21, HE staining showed there emerged some changes in the lung tissue of guinea pigs of RSV/OVA group which in accord with asthmatic pathologic changes, such as significant inflammatory cells infiltration, airway contraction, increased excretion and so on.③Airway responsiveness and M2 receptor function: Without electrical stimulation of the vagus nerves, the IPs of the four groups were: 10.46±1.55 mmH2O, 10.2±1.37 mmH2O, 12.11±1.88 mmH2O, 16.23±2.28mmH2O, which had no significant difference (P>0.05). After stimulation, IPs of all groups increased according to stimulating frequency. IP of RSV/NS group had no significant difference from that of Hep-2/NS group (P>0.05), but IP of Hep-2/OVA group was much higher than those of Hep-2/NS and RSV/NS groups (both P<0.05), and IP of RSV/OVA group was higher than that of Hep-2/OVA group (P<0.05). After giving pilocarpine intravenously, IPs of Hep-2/NS group, RSV/NS group and Hep-2/OVA group all decreased according to the doses of pilocarpine, but the extent of decrease of Hep-2/OVA group was much less than that of Hep-2/NS group and RSV/NS group (both P<0.05). IP of RSV/OVA group seemed to have few change and the extent of decrease was much less than RSV/NS group (P<0.05). Positive cholinergic fibers in smooth muscle: There was no significant difference between Hep-2/NS group and RSV/NS group (P>0.05), and Hep-2/OVA group was higher than Hep-2/NS group and RSV/NS group (both P<0.05), but there was no significant difference between Hep-2/OVA group and RSV/OVA group (P>0.05).Conclusions:①RSV infection could cause dysfunction of M2 autoreceptor on the airway postganglionic cholinergic nerves, then results in airway hyperresponsiveness. Also could cause pulmonary inflammation in term of neutrophils and eosinophils infiltrating into lung.②RSV infection and OVA inhalation could cause asthmatic pathologic changes in lung tissue of guinea pigs.③The AR and function of M2 receptor recovered to normal lever at the end stage of RSV infection. But RSV infection could enhance OVA-induced airway hyperresponsiveness, which maybe associate with the dysfunction of M2 autoreceptor on the airway postganglionic cholinergic nerves.OVA could increase the expression of positive cholinergic fibers in smooth muscle in airway, but RSV had no significant impact on it.
|
PDF Full Text Request