CHARACTERIZATION OF ALPHA-ADRENOCEPTOR SUBTYPE(S) MEDIATING VASOCONSTRICTION IN THE PERFUSED RABBIT OVARIAN VASCULAR BED

1 alpha(1)-Adrenoceptor agonists, noradrenaline, phenylephrine, methox amine, oxymetazoline and SDZ NVI 085 but not alpha(2)-adrenoceptor ago nists, UK 14304, tizanidine or clonidine evoked dose-dependent vasocon striction of the isolated perfused rabbit ovarian vascular bed. The ra nk order of agonist potency was noradenaline > oxymetazoline > phenyle phrine > SDZ NVI 085 > methoxamine. 2 Prazosin (10(-8) M-10(-5) M) dis placed agonist dose-response curves to the right. The pA(2)/pK(B) valu es 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 oxy metazoline (pA(2) 6.38). Yohimbine (10(-6) M-10(-5) M) was not very ef fective against any of the agonists. 3 WE 4101 (10(-8) M-10(-5) M) dis placed agonist dose-response curves to the right. The pA(2)/pK(B) valu es ranged between 7.08 and 7.93 against noradrenaline, phenylephrine, methoxamine and SDZ NVI 085. WB 4101 was significantly less potent aga inst oxymetazoline (pK(B) 6.85). 4 SZL-49 (5 x 10(-6) M) but not chlor oethylclonidine (3 x 10(-5) M) significantly reduced vasoconstrictor r esponses to all the agonists. 5 Electrical field stimulation of the ov arian bed produced frequency-dependent vasoconstrictor effects which w ere abolished by 6-OHDA. The responses were also antagonized in a conc entration-dependent by prazosin (10(-7) M-10(-5) M) and WE 4101 (3 x 1 0(-8) M-3 x 10(-7) M). Yohimbine reduced the response to electrical st imulation by 20% at 10(-5) M. The vasoconstrictor effect was also inhi bited by SZL-49 but not by chloroethylclonidine. 6 These results would suggest that the vasoconstrictor responses of the ovarian vascular be d to adrenergic agonists and to electrical stimulation are mediated vi a the alpha(1A)-adrenoceptor subtype.