Modulation of alpha 2-adrenergic receptors of rat vas deferens by adenosine receptors.
The effects of adenosine and its derivatives on binding of alpha 2-adrenergic receptor ligands with homogenates of rat vas deferens were examined. Adenosine and 2-chloradenosine increased the amount of [3H]clonidine binding. ATP had a slight effect, but AMP and adenine had none. The effect of adenosine was inhibited by theophylline. On the other hand, [3H]yohimbine binding was not influenced by 2-chloradenosine. The inhibitory effect of clonidine on [3H]yohimbine binding was strengthened by 2-chloradenosine, indicating an increase in affinity of alpha 2-adrenergic receptors for clonidine. Similar results were obtained with intact rat vas deferens pretreated with 2-chloradenosine. Then, it was found that presynaptic inhibition of noradrenaline release by clonidine was increased by pretreatment with 2-chloradenosine as judged by the contractile response of vas deferens induced by electrical stimulation. From these results it was concluded that adenosine and its derivatives cause a configurational change in presynaptic alpha 2-adrenergic receptors through activation of adenosine receptors. The induced configuration of alpha 2-receptors with high affinity for agonists seemed to be that of the active functional state, because the inhibitory effect of clonidine on norepinephrine release was potentiated by pretreatment with 2-chloradenosine.
D015762:2-Chloroadenosine; D000241:Adenosine / Q000031:analogs & derivatives / Q000494:pharmacology*; D000818:Animals; D001665:Binding Sites / Q000187:drug effects; D003000:Clonidine / Q000378:metabolism; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects*; D011956:Receptors, Cell Surface / Q000502:physiology*; D011983:Receptors, Purinergic; D014649:Vas Deferens / Q000502:physiology*; D015016:Yohimbine / Q000378:metabolism
D011942:Receptors, Adrenergic, alpha; D011956:Receptors, Cell Surface; D011983:Receptors, Purinergic; D015762:2-Chloroadenosine; D015016:Yohimbine; D000241:Adenosine; D003000:Clonidine