<prompt> Which of the following is true about dobutamine?It is a strong vasoconstrictorIt significantly increase hea rateIt reduces afterloadIt is a potent bronchodilator  <response>: 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. 