17β-Aminoestrogens induce guinea pig airway smooth muscle hyperresponsiveness through L-type Ca(2+) channels activation

Abstract

Therapy with estrogens is frequently used in menopausal women and as hormonal contraception. Because of its thrombotic effects, long term estrogen administration used in hormonal replacement therapy (HRT) and contraception could represent a health hazard. In this regard, 17β-aminoestrogens such as aminoestrol, butolame and pentolame have shown promising HRT potential, because they have a weak agonist estrogenic action and antithrombotic activity. Additionally, estrogens play a protective role in airway smooth muscle, but the effect of 17β-aminoestrogens on the airway smooth muscle has not been tested yet. In guinea pig tracheal smooth muscle pentolame and butolame induced hyperresponsiveness to histamine (His), carbachol (Cch) and KCl. Interestingly, aminoestrol did not show this effect at the highest concentration studied, it even lowered the contraction induced by Cch. The hyperresponsiveness induced by pentolame to His was abolished by nifedipine. In single tracheal myocytes, KCl induced an increment in the intracellular Ca(2+) concentration [Ca(2+)]i, pentolame also showed an increase in [Ca(2+)]i and the addition of KCl in the plateau of this rise further significantly augmented the [Ca(2+)]i response. Additionally, in patch clamp experiments pentolame increased the L-type Ca(2+) currents. Thus, 17β-aminoestrogens such as pentolame and butolame, but not aminoestrol, activate L-type Ca(2+) channel to induced hyperresponsiveness to Cch, His and KCl in guinea pig tracheal smooth muscle. Due to its lack of effect on airways and to its anticoagulant characteristics, aminoestrol seems to be the best alternative in the HRT among the 17β-aminoestrogens studied.

Keywords: 17β-Aminoestrogens; Airway hyperresponsiveness; L-type Ca(2+) channels; Tracheal smooth muscle.