An interaction between prejunctional alpha-adrenoceptors and prejunctional beta-adrenoceptors.
The ability os isoprenaline to enhance transmitter release from sympathetic nerves in rat atria incubated with [3H]noradrenaline was assessed under three conditions of prejunctional alpha-adrenoceptor activation: in the presence of phentolamine, in the presence of noradrenaline, and in the absence of either drug. Isoprenaline-induced enhancement of transmitter release was inversely related to the degree of activation of prejunctional alpha-adrenoceptors. Thus there appears to be an interaction between the prejunctional alpha-adrenoceptor inhibitory mechanism and the prejunctional beta-adrenoceptor facilitatory mechanism. In rabbit ear arteries incubated with [3H]noradrenaline, isoprenaline facilitated transmitter release in the presence but not in the absence of phentolamine. Therefore in some tissues it may be necessary to block prejunctional alpha-adrenoceptors before prejunctional beta-adrenoceptors can be demonstrated.
D000818:Animals; D001158:Arteries / Q000378:metabolism; D005260:Female; D006325:Heart Atria / Q000378:metabolism; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D009433:Neural Inhibition; D009638:Norepinephrine / Q000378:metabolism*; D010646:Phentolamine / Q000494:pharmacology; D011817:Rabbits; D051381:Rats; D011941:Receptors, Adrenergic / Q000502:physiology*; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000502:physiology*; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000502:physiology*
D011941:Receptors, Adrenergic; D011942:Receptors, Adrenergic, alpha; D011943:Receptors, Adrenergic, beta; D007545:Isoproterenol; D009638:Norepinephrine; D010646:Phentolamine