EFFECTS OF ESTROGEN PRETREATMENT OF THE SPARE ALPHA-1-ADRENOCEPTORS AND THE SLOW AND FAST COMPONENTS OF THE CONTRACTILE RESPONSE OF THE ISOLATED FEMALE RAT AORTA

1. Estrogen pretreatment increases the responsiveness to noradrenaline and to clonidine in isolated rat female aortae. 2. Determinations of the pK(A) and pA2 of noradrenaline and prazosin, respectively suggest that the isolated female aorta possess a homogeneous alpha-1-adrenoceptor population. 3. The fast and slow components of clonidine-induced aorta contraction were determined using nifedipine. 4. Considering that after estrogen pretreatment, an increase in spare alpha-1-adrenoceptors probably occur and only the fast component of clonidine-induced contraction was enhanced we concluded that estrogen pretreatment increases the number of alpha-1-adrenoceptors and the amount of intracellular calcium available for contraction.