Relationship between tyramine potentiation and selective inhibition of monoamine oxidase types A and B in the rat vas deferens.
1 The degree of selective monoamine oxidase (MAO) inhibition produced by (-)-deprenyl, clorgyline, LY51641 and tranylcypromine was examined in relation to modification of tyramine and noradrenaline contractile responses of the rat isolated vas deferens. 2 All inhibitors possessed reversible alpha-adrenoceptor blocking activity, determined against noradrenaline on the denervated vas deferens. For LY51641 and tranylcypromine, antagonism was competitive, with pA2 values of 6.17 and 5.16. 3 Clorgyline, LY51641 and (-)-deprenyl (10(-5) M) inhibited the tyramine response while present in the organ bath: LY51641, which was the most potent as an alpha-adrenoceptor blocker, produced this effect at 10(-6) M. Responses to tyramine and noradrenaline were potentiated on wishing out the inhibitors, but noradrenaline potentiation was seen only when tyramine had been present in the system. 4 Tranylcypromine (10(-6) M) potentiated responses to noradrenaline and tyramine while present in the organ bath. 5 Potentiation of tyramine responses by clorgyline and LY51641 occurred at 91% and 64% inhibition of MAO type A respectively, although full potentiation of the tyramine response was elicited only when substantial inhibition of both enzyme types occurred. Selective inhibition of MAO type B by 67% (with deprenyl) was not associated with tyramine potentiation.
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D003714:Denervation; D066298:In Vitro Techniques; D008297:Male; D008995:Monoamine Oxidase / Q000378:metabolism; D008996:Monoamine Oxidase Inhibitors / Q000494:pharmacology*; D009130:Muscle, Smooth / Q000187:drug effects*; D009638:Norepinephrine / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D014439:Tyramine / Q000494:pharmacology*; D014649:Vas Deferens / Q000187:drug effects
D000317:Adrenergic alpha-Antagonists; D008996:Monoamine Oxidase Inhibitors; D008995:Monoamine Oxidase; D009638:Norepinephrine; D014439:Tyramine