Characterization of alpha-adrenoceptor subtype(s) mediating vasoconstriction in the perfused rabbit ovarian vascular bed.

Abstract

1. alpha 1-Adrenoceptor agonists, noradrenaline, phenylephrine, methoxamine, oxymetazoline and SDZ NVI 085 but not alpha 2-adrenoceptor agonists, UK 14304, tizanidine or clonidine evoked dose-dependent vasoconstriction of the isolated perfused rabbit ovarian vascular bed. The rank order of agonist potency was noradenaline > oxymetazoline > phenylephrine > SDZ NVI 085 > methoxamine. 2. Prazosin (10(-8) M - 10(-5) M) displaced agonist dose-response curves to the right. The pA2/pKB values ranged between 7.27 and 7.66 against noradrenaline, phenylephrine, methoxamine and SDZ NVI 085 and were not significantly different from each other. Prazosin was however significantly less potent against oxymetazoline (pA2 6.38). Yohimbine (10(-6) M - 10(-5) M) was not very effective against any of the agonists. 3. WB 4101 (10(-8) M - 10(-5) M) displaced agonist dose-response curves to the right. The pA2/ pKB values ranged between 7.08 and 7.93 against noradrenaline, phenylephrine, methoxamine and SDZ NVI 085. WB 4101 was significantly less potent against oxymetazoline (pKB 6.85). 4. SZL-49 (5 x 10(-6) M) but not chloroethylclonidine (3 x 10(-5) M) significantly reduced vasoconstrictor responses to all the agonists. 5. Electrical field stimulation of the ovarian bed produced frequency-dependent vasoconstrictor effects which were abolished by 6-OHDA. The responses were also antagonized in a concentration-dependent by prazosin (10(-7) M - 10(-5) M) and WB 4101 (3 x 10(-8) M - 3 x 10(-7) M). Yohimbine reduced the response to electrical stimulation by 20% at 10(-5) M. The vasoconstrictor effect was also inhibited by SZL-49 but not by chloroethylclonidine. 6. These results would suggest that the vasoconstrictor responses of the ovarian vascular bed to adrenergic agonists and to electrical stimulation are mediated via the alpha 1A-adrenoceptor subtype.