Dopamine antagonizes the actions of angiotensin II in renal brush-border membrane.

In the present study, we examined the effects of dopamine and angiotensin II (ANG II) in renal brush-border membrane (BBM). With isolated BBM vesicles, dopamine (> 10(-4) M) directly inhibited BBM 22Na+ uptake and activated phospholipase C (PLC). These effects were mimicked by DA1 agonist but not DA2 agonist and were prevented by DA1 antagonist but not DA2 antagonist, indicating the involvement of DA1 receptors. In contrast to dopamine, ANG II directly stimulated BBM 22Na+ uptake and activated BBM phospholipase A2 (PLA2). Neither dopamine nor ANG II altered BBM adenosine 3',5'-cyclic monophosphate content. In the presence of dopamine, ANG II failed to stimulate BBM Na+ uptake and PLA2. However, both DA1 and DA2 agonists similarly abrogated the actions of ANG II, and both DA1 and DA2 antagonists were required to restore ANG II actions in the presence of dopamine, indicating the involvement of both DA1 and DA2 receptors in the antagonistic effect of dopamine. Dopamine, as well as DA1 or DA2 agonists, also lowered 125I-ANG II BBM binding. In summary, these results show that, in renal BBM, dopamine impedes ANG II receptor binding and antagonizes the stimulatory effects of ANG II on Na+ uptake and PLA2. This occurred through both DA1 and DA2 receptors and independent of DA1 effects on BBM Na+ uptake or PLC.