Interactions of the enantiomers of 3-O-methyldobutamine with alpha- and beta-adrenoceptors in vitro.
The enantiomers of 3-O-methyldobutamine, a metabolite of dobutamine, were evaluated for their alpha- and beta-adrenoceptor mediated effects in vitro in a variety of isolated organs and in radioligand binding studies. Neither enantiomer of 3-O-methyldobutamine possessed alpha 1-adrenoceptor agonist activity in isolated guinea pig aorta. However, both enantiomers of 3-O-methyldobutamine were competitive alpha 1-adrenoceptor antagonists, with the (+)-enantiomer being approximately 10-fold more potent than the (-)-enantiomer as assessed either in guinea pig aorta or by displacement of 3H-prazosin binding from alpha 1-adrenoceptors in rat cerebral cortex. The alpha 1-adrenoceptor blocking activity of (+)-3-O-methyldobutamine was relatively potent and corresponded to a pA2 of 7.33 in guinea pig aorta and a -log Ki of 7.72 in radioligand binding studies. Neither enantiomer of 3-O-methyldobutamine possessed alpha 2-adrenoceptor agonist activity in field-stimulated guinea pig ileum. Although (+)-3-O-methyldobutamine weakly inhibited the twitch response in field-stimulated guinea pig ileum, the response was not blocked by the selective alpha 2-adrenoceptor antagonist, yohimbine, and was found to result from weak anticholinergic activity (pA2 = 5.06). Neither enantiomer of 3-O-methyldobutamine possessed beta 1-adrenoceptor agonist activity in guinea pig atria, however the (+)-enantiomer was a weak noncompetitive antagonist at beta 1-adrenoceptors. In contrast, both enantiomers of 3-O-methyldobutamine were weak beta 2-adrenoceptor agonists in rat uterus, however these weak effects were not highly stereoselective, which was also confirmed in radioligand binding studies.(ABSTRACT TRUNCATED AT 250 WORDS)
Ruffolo
R R
RR
Messick
K
K
Horng
J S
JS
D000818:Animals; D001667:Binding, Competitive; D002395:Catecholamines / Q000494:pharmacology*; D002540:Cerebral Cortex / Q000378:metabolism; D004082:Dihydroalprenolol / Q000378:metabolism; D004280:Dobutamine / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology*; D006168:Guinea Pigs; D006339:Heart Rate / Q000187:drug effects; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects; D011224:Prazosin / Q000378:metabolism; D051381:Rats; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects* / Q000378:metabolism; D011943:Receptors, Adrenergic, beta / Q000187:drug effects* / Q000378:metabolism; D013237:Stereoisomerism
D002395:Catecholamines; D011942:Receptors, Adrenergic, alpha; D011943:Receptors, Adrenergic, beta; D004280:Dobutamine; D004082:Dihydroalprenolol; C044730:3-O-methyldobutamine; D011224:Prazosin