Which of the following is true about dobutamine?

Ans. is 'a' i.e., It is a strong vasoconstrictor Dobutamine acts on both a and b receptors. o But on clinically employed dose only b, action is prominent i.e. an increase in force of cardiac contraction and output without a significant change in hea rate, BP and peripheral resistance. o Now you must be thinking, why I have given option 'a' as the answer. Read below: o Dobutamine consists of two isomer: i) (+) isomer is potent [b1-agonist and a1 antagonist ii) (-) isomer is a potent a1 agonist o Normally action of (+) isomer predominates o But, when (-) isomer is given alone it causes significant vasoconstriction due to a1 agonistic action.