A possible mechanism of action of a beta-adrenergic partial agonist (carteolol) in guinea pig taenia caecum.
Carteolol, 5-(3-tert-butylamino-2-hydroxy)propoxy-3, 4-dihydrocarbostyril hydrochloride was found to be a beta-adrenergic partial agonist in the taenia caecum of guinea pig. Concentration response curves of carteolol and isoprenaline were parallelly shifted by propranolol (10(-7) M) suggesting that site of action of both the drugs was the same beta-adrenoceptor. The pD2-values of carteolol obtained from the concentration action curves in mechanical response and increase of tissue concentration of cyclic AMP were significantly different from its pA2-value against isoprenaline and its pKi-value (negative log of its apparent dissociation constant). A possible explanation of our observation would seem to be as follows. Carteolol and isopranaline interact with the same beta-adrenoceptor where there may be two different sites: a binding site for agonist and binding site for antagonist.
D000818:Animals; D002354:Carteolol / Q000494:pharmacology*; D002432:Cecum / Q000187:drug effects; D000242:Cyclic AMP / Q000378:metabolism; D004082:Dihydroalprenolol; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects*; D011412:Propanolamines / Q000494:pharmacology*; D011506:Proteins / Q000378:metabolism
D011412:Propanolamines; D011506:Proteins; D004082:Dihydroalprenolol; D002354:Carteolol; D000242:Cyclic AMP; D007545:Isoproterenol