Effects of reserpine and adenosine agonist on ?(2)-adrenergic receptor of rat vas deferens examined with [(3)H]yohimbine and [(3)H]clonidine.
The changes of [(3)H]yohimbine and [(3)H]clonidine binding sites in rat vas deferens on treatments with adenosine receptor agonists (2-chloroadenosine, adenosine) or reserpine were examined. Treatment with adenosine agonist in vitro increased [(3)H]clonidine binding sites but had no influence on affinity and number of binding sites of ?(2)-antagonist, [(3)H]yohimbine. Amount of [(3)H]yohimbine binding sites was found to be higher than that of [(3)H]clonidine with or without the treatment. Inhibition curves of ?(2)-agonists, clonidine and norepinephrine, on [(3)H]yohimbine binding were less than unity though ?(2)-antagonist inhibited with about 1.0 of n(H). The treatment with adenosine agonist reduced the IC(50) value of agonists on the [(3)H]yohimbine binding but had no influence on the inhibitory effect of antagonist. These effect of adenosine agonists was completely blocked by theophylline. Accordingly it was considered that activation of adenosine receptor caused configurational change in ?(2)-adrenergic receptor from low affinity state for agonist to the high affinity state, though both states had same affinity for antagonist. On the other hand, treatment with reserpine in vivo increased the affinity of clonidine for ?(2)-adrenergic receptors and also increased the amount of the ?(2)-receptors.
Watanabe
Y
Y
Department of Pharmacology 1, Osaka University School of Medicine, Kita-ku, Osaka 530, Japan.
Kagiya
T
T
Kaminoh
Y
Y
Lai
R T
RT
Osugi
T
T
Yoshida
H
H