Effect of dopamine on kidney is blocked by-

Ans. is 'd' i.e., Haloperidol Antagonism of dopamine actions o As the receptors stimulated by dopamine are different at different rates of infusion, the antagonists are different for different rates of infusion. Antagonism of renal dose o Low rates of dopamine infusion cause stimulation of dopamine receptors and produce vasodilatation of renal and mesentric blood vessels. o This vasodilatation of dopamine is not antagonised by the J3-adrenoreceptor blockers (as this renal effect is not mediated by [3-receptors). o However this vasodilatation of renal vessels is antagonized by halopridol and other dopamine receptor blocking agents. Antagonism of intermediate dose o The infusion of moderately higher concentrations of dopamine increases the rate and contractile force of the hea and augments the cardiac output. o This action is mediated by piadrenoreceptor and due to nor-adrenaline release, and is antagonized by propranolol. Antagonism of higher doses o At still higher concentrations, dopamine causes a-adrenoreceptor - mediated vasoconstriction in most vascular beds and stimulates the hea. o The vasoconstrictive action of dopamine is antagonized by a-adrenoreceptor blocking agents such as phentolamine.