INFLUENCE OF ESTROGEN REPLACEMENT THERAPY ON AIRWAY REACTIVITY

The effect of estrogen on smooth muscle in various organs is unpredict able. Little is known about the effect of estrogen on respiratory trac t smooth muscle, particularly in humans. In the present study we used the histamine challenge test (HCT) to assess the effect of estrogen re placement therapy (ERT) on airway reactivity in postmenopausal women w ho did not suffer from respiratory disease. Thirty-six women who were undergoing treatment at the postmenopausal clinic completed the study. All participants were nonsmokers whose pulmonary function tests were normal. HCT was performed twice before the inception of ERT, and a thi rd time 4-6 weeks after ERT was begun. None of the 36 women demonstrat ed a 20% decrease in FEV(1) values (PC20) after inhaling histamine at a concentration of 8 mg/ml, either before or during ERT. The maximal d ecrease in FEV(1) values in response to the maximum concentration of h istamine was significantly lower during ERT compared to the pretreatme nt period. The average maximal decrease in FEV(1) during ERT was 2.63 +/- 2.72% (mean +/- DS) compared to 5.21 +/- 4.47% and 6.57 +/- 5.28% on the 2 tests prior to therapy (p < 0.0002). We conclude that ERT has an inhibitory effect on the bronchial reactivity of respiratory smoot h muscle. There is no cause for concern about increased airway reactiv ity as an adverse effect of this therapy.