Abstract
Employing the isolated rat portal vein for testing (+/-) dobutamine, and its (+) and (-) enantiomers, we have confirmed the results obtained by Ruffolo et al (1981, 1983) using different methods. In the rat portal vein, (-) dobutamine acts as an alpha agonist, less potent than noradrenaline. The racemate acts as an alpha-agonist with about half the potency of (-) dobutamine. The (+) isomer shows no effects. In the presence of the alpha blocker BE 2254, all compounds, (+/-), (+) and (-) dobutamine, showed dose-dependent beta effects. These were surely the result of the action on beta 2 adrenoceptors since they could be antagonized by the potent and specific beta 2 antagonist ICI 118-551. We have found that (+) dobutamine is, as a beta 2 agonist, 355 to 1,480 times less potent than isoprenaline and 12-16 times more potent than (-) dobutamine. The pA2 of ICI 118-551 against (+) dobutamine is 9.36 (+/- 0.04). This high value is further proof that the beta receptor population of the rat portal vein is beta 2.
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