Evidence for pharmacological similarity between α₂,‐adrenoceptors in the vas deferens and central nervous system of the rat

Abstract

1 Seven a2-adrenoceptor antagonists with diverse chemical structures have been examined for their effects at a2-adrenoceptors in the vas deferens and central nervous system of the rat. 2 Antagonist potency assessed against the presynaptic a2-adrenoceptor agonist action of clonidine in the isolated vas deferens (RX 781094 > Wy 26703 > yohimbine > rauwolscine > piperoxan > mianserin > RS 21361) was highly correlated with the ability of these drugs to displace saturable [3H]-RX 781094 binding from cerebral cortex membranes. 3 Similarly, antagonist potency in the vas deferens was highly correlated with antagonist activity in reversing the centrally-mediated mydriasis induced by the selective a2-adrenoceptor agonist, guanoxabenz, in pentobarbitone-anaesthetized rats. 4 The results indicate that the presynaptic a2-adrenoceptors in the vas deferens are pharmacologically similar to characterized these a2-adrenoceptors in the central nervous system of the rat.

Changes in Prejunctional Potency of B‐ht 933 During Aging in the Rat Vas Deferens

“…It has been previously shown the az-adrenoceptor agonists produce concentration-dependent inhibition of nerve-evoked contraction in the vas deferens by acting at prejunctional a2-adrenoceptors (MacDonald & McGrath 1980). Indeed the pA2 value for rauwolscine in antagonizing the inhibitory effect of B-HT 933 in both sections of vasa deferentia in both age categories, is consistent with the affinity of this antagonist at al-adrenoceptors (Doxey et al 1983).…”

Affinities of Adrenergic Drugs for α₂-Adrenoceptors in Dog Saphenous Vein in Comparison with Those in Rat Brain or Human Platelets

“…[ 1983] have reported that the properties of (^-adrenoceptors in guinea pig kidney and human platelets are similar to those in calf cerebral cortex. The similarity between ct2-adrenoceptors in the vas deferens and in central nervous system of the rat has been reported by Doxey et al [ 1983], It seems that the affinities of drugs for central (^-adrenoceptors are similar to those for peripheral ct2-adrenoceptors.…”

“…Thus, it is likely that the binding of drugs to a low-affin ity form but not to a high-affinity form of a.2-adrenoceptors correlates with the a 2-adrenoceptor-mediated response in the saphenous vein. Doxey et al [1983] also came to the sim ilar conclusion, although they did not use experimental conditions in which the highl and low-affinity forms of {^-adrenoceptors were clearly discriminated with GTP. Kahn et al [1982] and Woodcock and Johnson [1982] have reported that the affinities of adrenergic drugs for inhibition of adenylate cyclase highly correlated with their affinities for the low-affinity form of a 2-adrenoceptors in NG 108-15 cells and rat renal cortex.…”

Pharmacological profile of the novel .ALPHA.-adrenoceptor antagonist KT-611(naftopidil).

“…This affinity was approximate ly 10 times lower than the affinity at the post junctional a2-adrenoceptors of the dog saphe nous vein (pA2 = 6.77). This discrepancy may reflect the different affinities of KT-611 to prejunctional and postjunctional a2-adreno ceptors, because pharmacological resemblance of a2-adrenoceptors in rat cerebral cortex and rat vas deferens has been reported (16).…”