The present study investigated the hypothesis that the duration of ovarian hormone deprivation before reintroduction of oestrogen affects the role of oestrogen as a mediator of the contractile function of α1-adrenergic receptors. Rats underwent ovariectomy (OVX) or were sham-operated, and the OVX rats were treated with vehicle (corn oil) or 17β-oestradiol (E2) for 5 days either 10, 28 or 60 days after OVX. The OVX increased phenylephrine- and Ca2+-induced contractions. Interestingly, the phenylephrine-induced contractions were increased at each of the three time points, whereas the Ca2+-induced contractions were only increased in the 60-day group. E2 had biphasic effects on phenylephrine- and Ca2+-induced contractility. Indeed, E2 increased contractions in the 10-day group and diminished contractions in the other groups (the increased contractions were avoided by verapamil). These results indicate that E2 controls α1-adrenergic receptor-mediated contractility through effects on L-type Ca2+ channels in a way that depends on the timing in which the treatment with E2 is initiated.
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