Role of Estrogen Receptor-Alpha in an Experimental Model of Bronchial Asthma

Background: Use of hormone replacement therapy (HRT) may increase the risk of adult-onset asthma in women. Various in vitro studies have reported that estradiol stimulates human mast cell lines causing release of allergic mediators which was not observed in estrogen receptor-alpha (ER-alpha) knockout mice. Thus, estrogen might be a key element in occurrence of asthma. In the present study, we proposed to determine the role of ER-alpha in an experimental model of bronchial asthma. Methods: Trypsin and egg albumin induced chronic model of asthma were used. On the 28th day, various parameters such as pO2 level, serum bicarbonate level, tidal volume, respiratory rate, air flow rate, differential white blood cells count in the bronchoalveolar lavage (BAL) fluid and serum cholesterol level were measured as well as lung histopathological examination and uterine weight measurement were carried out. Results: Estradiol treatment resulted in lower pO2 level, tidal volume and air flow rate. Also, serum bicarbonate level, respiratory rate and eosinophil rate and eosinophil count in BAL fluid were higher as compared to asthmatic control group. These effects were not observed in methyl-piperidino-pyrazole (MPP) co-treated group. Histopathological data suggested that the destruction of alveolar and muscular layers was more prominent in estradiol-treated group than asthmatic control and MPP co-treated groups. Estradiol-treated group showed lower total serum cholesterol levels and higher uterine weight as compared to asthmatic control group which was not observed in MPP co-treated group indicating antagonism of estradiol by MPP at ER-alpha receptor. Conclusion: Estrogen seems to have a strong promoting effect on pathogenesis of bronchial asthma via ER-alpha receptors.