dopamine receptor regulation of reactive oxygen species production, NADPH oxidase, and blood pressure. Am J Physiol Regul Integr Comp Physiol 290: R96 -R104, 2006; doi:10.1152/ajpregu.00434.2005.-Activation of D1-like receptors (D 1 and/or D5) induces antioxidant responses; however, the mechanism(s) involved in their antioxidant actions are not known. We hypothesized that stimulation of the D 5 receptor inhibits NADPH oxidase activity, and thus the production of reactive oxygen species (ROS). We investigated this issue in D 5 receptor-deficient (D5Ϫ/Ϫ) and wild-type (D 5ϩ/ϩ) mice. NADPH oxidase protein expression (gp91 phox , p47 phox , and Nox 4) and activity in kidney and brain, as well as plasma thiobarbituric acid-reactive substances (TBARS) were higher in D 5Ϫ/Ϫ than in D5ϩ/ϩ mice. Furthermore, apocynin, an NADPH oxidase inhibitor, normalized blood pressure, renal NADPH oxidase activity, and plasma TBARS in D 5Ϫ/Ϫ mice. In HEK-293 cells that heterologously expressed human D 5 receptor, its agonist fenoldopam decreased NADPH oxidase activity, expression of one of its subunits (gp91 phox ), and ROS production. The inhibitory effect of the D 5 receptor activation on NADPH oxidase activity was independent of cAMP/PKA but was partially dependent on phospholipase D2. The ability of D5 receptor stimulation to decrease ROS production may explain, in part, the antihypertensive action of D 5 receptor activation. hypertension DURING THE PAST DECADE, DOPAMINE has been shown as an important regulator of blood pressure, sodium balance, and renal and adrenal function through an independent peripheral dopaminergic system (32). Dopamine exerts its actions via two families of cell surface receptors that belong to the superfamily of G protein-coupled receptors. D 1 -like receptors (D 1 and D 5 ) stimulate adenylyl cyclases, while D 2 -like receptors (D 2 , D 3 , and D 4 ) inhibit adenylyl cyclases (32,45). Abnormal signaling of D 1 -like receptors has been shown to be involved in rodent models of genetic hypertension and in humans with essential hypertension (7,10,17,28,32,55). However, the precise D 1 -like receptor involved remains to be determined. There is an abnormal renal D 1 function in hypertension, which is caused by activated variants of the G protein-coupled receptor kinase type 4 (16, 32). The D 5 locus is not linked to hypertension in Dahl salt-sensitive rats (22), and mutations of the D 5 are not found in spontaneously hypertensive rats (3). However, the locus of the human D 5 (hD 5 ), 4p15.1-16

Abstract-The ability of the dopamine-1 (D 1 )-like receptor to stimulate adenylyl cyclase (AC) and phospholipase C (PLC), inhibit sodium transport in the renal proximal tubule (RPT), and produce natriuresis is attenuated in several rat models of hypertension. Since the inhibitory effect of D 1 -like receptors on RPT sodium transport is also reduced in some patients with essential hypertension, we measured D 1 -like receptor coupling to AC and PLC in cultures of human RPT cells from normotensive (NT) and hypertensive (HT) subjects. Basal cAMP concentrations were the same in NT (nϭ6) and HT (nϭ4). However, the D 1 -like receptor agonist fenoldopam increased cAMP production to a greater extent in NT (maximum responseϭ67Ϯ1%) than in HT (maximum responseϭ17Ϯ5%), with a potency ratio of 105. Dopamine also increased cAMP production to a greater extent in NT (32Ϯ3%) than in HT (14Ϯ3%). has been shown to be a paracrine regulator of sodium transport in humans and in animals during sodium-replete conditions. 1 During states of positive sodium balance, endogenous renal dopamine facilitates sodium excretion caused by a decrease in proximal as well as distal ion and water transport. [1][2][3][4][5] The natriuretic effect of exogenous and endogenous renal dopamine (and dopamine-1 [D 1 ]-like receptor agonists) is impaired in 2 animal models of hypertension. 1 In the spontaneously hypertensive rat (SHR), the impaired natriuretic effect of dopamine and D 1 -like receptor agonists is associated with a decreased ability to inhibit Na ϩ -H ϩ exchanger 1,3,6 and Na ϩ ,K ϩ -ATPase activity in RPT. 3,7,8 The decreased ability of dopamine and D 1 -like receptor agonists to inhibit these transporters has been related to a defective dopaminergic stimulation of second messenger production by adenylyl cyclase (AC), phospholipase C (PLC), and phospholipase A 2 . 6 -10 These phenotypes may be manifestations of a defective gene important in controlling blood pressure, since the defective dopaminergic regulation of RPT transport and sodium excretion cosegregates with hypertension in rats, and disruption of one of the D 1 -like receptor genes (D 1A receptor) in mice produces hypertension. 6 A defective regulation of renal proximal tubule sodium transport by D 1 -like receptors is also present in human essential hypertension. 11,12 We hypothesized that the coupling between a D 1 -like receptor and the G protein/effector enzyme complex may also be defective in some patients with essential hypertension, similar to that seen in animal models of genetic hypertension. Therefore, we compared the effect of dopamine and fenoldopam on AC and PLC activity in human RPT in culture.

Abstract-TheT he proximal tubule is the major site of sodium and water reabsorption in the mammalian nephron. Paracrine regulation of sodium reabsorption in the proximal tubule by the renin/angiotensin system occurs via several angiotensin receptor subtypes (AT 1 , AT 2 , and AT 4 ). [1][2][3][4][5] The activation of angiotensin II type 1 (AT 1 ) receptors by angiotensin II increases sodium transport, whereas the activation of AT 2 and AT 4 receptors decreases sodium reabsorption in this nephron segment. [1][2][3][4][5] However, in physiological conditions, the major effect of angiotensin II on sodium transport is stimulatory, via AT 1 receptors. 1,2,6 The dopaminergic system also exerts a paracrine regulatory role on renal sodium transport in the proximal tubule. 7,8 Dopamine receptors, like the angiotensin II receptors, are expressed in brush border and basolateral membranes of RPTs. 8 -11 In contrast to the stimulatory effect of angiotensin II on sodium transport in RPTs, the major consequence of the activation of dopamine receptors is an inhibition of sodium transport. 7,8 Inhibition of renal proximal tubular angiotensin II production or blockade of AT 1 receptors increases the natriuretic effect of the D 1 -like agonist, fenoldopam. 11 D 1 -like and D 2 -like receptor agonists also antagonize the stimulatory effect of angiotensin II, acting via AT 1 receptors, on renal proximal tubular luminal sodium transport. 12,13 The 2 D 1 -like (D 1 and D 5 ) and the 3 D 2 -like (D 2 , D 3 , and D 4 ) receptors are expressed in specific segments of the mammalian kidney. 7,8,14 -19 Whereas the D 4 receptor is expressed mainly in collecting ducts, the D 3 receptor, the major D 2 -like receptor, like the D 1 and D 5 receptors, is expressed in the proximal tubule. [7][8][9][10] The distribution of D 2 receptor protein along the nephron is still uncertain. 8,19 The effect of D 2 receptors on renal sodium transport is also not clear because of the lack of agonists that are highly selective to the D 2 over the D 3 receptor. 16,17 However, 7-OH-DPAT, a ligand with a 50-fold selectivity to the D 3 over the D 2 receptor, 16 increases sodium excretion in rats. 17 Moreover, D 3 receptor-null mice have a decreased ability to excrete an acute sodium load, whereas no such limitation is found in D 2 receptor-null mice. 18,19 We surmise that the D 3 receptor may be the D 2 -like subtype receptor that interacts with the AT 1 receptor in rat RPTs.Angiotensin and dopamine receptors are expressed in immortalized rat RPT cells. 20,21 These RPT cells have charOriginal