Action of aminoguanidine on the stomach of pylorus-ligated rats

Characterization of the innate immune response to chronic aspiration in a novel rodent model

Background

Although chronic aspiration has been associated with several pulmonary diseases, the inflammatory response has not been characterized. A novel rodent model of chronic aspiration was therefore developed in order to investigate the resulting innate immune response in the lung.

Methods

Gastric fluid or normal saline was instilled into the left lung of rats (n = 48) weekly for 4, 8, 12, or 16 weeks (n = 6 each group). Thereafter, bronchoalveolar lavage specimens were collected and cellular phenotypes and cytokine concentrations of IL-1alpha, IL-1beta, IL-2, IL-4, IL-6, IL-10, GM-CSF, IFN-gamma, TNF-alpha, and TGF-beta were determined.

Results

Following the administration of gastric fluid but not normal saline, histologic specimens exhibited prominent evidence of giant cells, fibrosis, lymphocytic bronchiolitis, and obliterative bronchiolitis. Bronchoalveolar lavage specimens from the left (treated) lungs exhibited consistently higher macrophages and T cells with an increased CD4:CD8 T cell ratio after treatment with gastric fluid compared to normal saline. The concentrations of IL-1alpha, IL-1beta, IL-2, TNF-alpha and TGF-beta were increased in bronchoalveolar lavage specimens following gastric fluid aspiration compared to normal saline.

Conclusion

This represents the first description of the pulmonary inflammatory response that results from chronic aspiration. Repetitive aspiration events can initiate an inflammatory response consisting of macrophages and T cells that is associated with increased TGF-beta, TNF-alpha, IL-1alpha, IL-1beta, IL-2 and fibrosis in the lung. Combined with the observation of gastric fluid-induced lymphocyitic bronchiolitis and obliterative bronchiolitis, these findings further support an association between chronic aspiration and pulmonary diseases, such as obliterative bronchiolitis, pulmonary fibrosis, and asthma.

Effect of intraduodenally administered histamine on gastric acid secretion in rats and guinea pigs

We examined the effect of histamine administered intraduodenally as well as subcutaneously or intravenously on the gastric acid secretion in rats and guinea pigs, using a newly devised cannula. Intraduodenally administered histamine dihydrochloride caused a significant dose-dependent increase in the gastric acid secretion in rats. The maximal acid secretion, which corresponded to that after subcutaneous (20 mg/kg) or intravenous (10 mg/kg/hr) administration of histamine, was observed within 30 min after intraduodenal administration (40 mg/kg). The plasma concentrations of histamine determined 30 min after intraduodenal, subcutaneous, and intravenous administration of histamine were nearly the same. Pretreatment with aminoguanidine sulfate (diamine oxidase inhibitor) at 30 mg/kg significantly increased the gastric acid secretion caused by intraduodenal histamine. The gastric acid secretion stimulated by intraduodenal histamine was significantly inhibited by cimetidine, pirenzepine, and omeprazole, but remained unchanged with tripelennamine. Intraduodenal histamine (20 mg/kg) also maximally stimulated the gastric acid secretion in guinea pigs. The response was comparable to that with subcutaneous histamine (1 mg/kg). We conclude that intraduodenal histamine has the ability to stimulate gastric acid secretion in both rats and guinea pigs.