The effects of 17β-oestradiol on increased α₁- adrenergic vascular reactivity induced by prolonged ovarian hormone deprivation: The role of voltage-dependent l-type ca channels

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.