Effect of histamine on two different affinity sites in beta-adrenoceptors.
1. To study the effect of histamine on two different affinity sites in beta-adrenoceptors, we tested specific binding of [3H]befunolol to microsomal fractions from the guinea pig taenia caecum in the presence and absence of histamine (10(-5) M). 2. The Scatchard plot of data in the absence of histamine was recognized as two straight lines suggesting the existence of two different affinity sites: high and low. However, a curvilinear plot with upward concavity was observed in the presence of histamine (10(-5) M). 3. These results suggest the possibility that histamine alters the binding sites of beta-adrenoceptors into several classes of sites with lower affinity. 4. Further, an antagonism between isoprenaline and BFE-55, which interacts only with the high affinity site, was tested on the atria (beta 1-adrenoceptor predominant) and tracheae (beta 2-adrenoceptor predominant) of the guinea pig. The pA2-values in the atria were almost equal to those in the trachea, suggesting that both beta 1- and beta 2-adrenoceptors contained two different affinity sites.
Takayanagi
I
I
Department of Chemical Pharmacology, Toho University School of Pharmaceutical Sciences, Chiba, Japan.
Koike
K
K
Ogishima
M
M
Hayashida
M
M
Fujii
M
M
D000318:Adrenergic beta-Agonists; D000818:Animals; D006168:Guinea Pigs; D006339:Heart Rate / Q000187:drug effects; D006632:Histamine / Q000494:pharmacology*; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects / Q000378:metabolism; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000378:metabolism; D011412:Propanolamines; D011943:Receptors, Adrenergic, beta / Q000187:drug effects*; D014132:Trachea / Q000187:drug effects / Q000378:metabolism
D000318:Adrenergic beta-Agonists; D011412:Propanolamines; D011943:Receptors, Adrenergic, beta; C052295:BFE 55; D006632:Histamine; D007545:Isoproterenol