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Escano CS, Armando I, Wang X, Asico LD, Pascua A, Yang Y, Wang Z, Lau YS, Jose PA. Renal dopaminergic defect in C57Bl/6J mice. Am J Physiol Regul Integr Comp Physiol 297: R1660-R1669, 2009. First published September 2, 2009; doi: 10.1152/ajpregu.00147.2009.--The C57Bl/6J mouse strain, the genetic background of many transgenic and gene knockout models, is salt sensitive and resistant to renal injury. We tested the hypothesis that renal dopaminergic function is defective in C57Bl/6J mice. On normal NaCl (0.8%, 1 wk) diet, anesthetized and conscious (telemetry) blood pressures were similar in C57Bl/6J and SJL/J mice. High NaCl (6%, 1 wk) increased blood pressure ([approximately equal to]30%) in C57Bl/6J but not in SJL/J mice and urinary dopamine to greater extent in SJL/J than in C57B1/6J mice. Absolute and fractional sodium excretions were lower in SJL/J than in C57Bl/6J mice. The blood pressure-natriuresis plot was shifted to the right in C57Bl/6J mice. Renal expressions of [D.sub.1]-like ([D.sub.1]R and [D.sub.5]R) and angiotensin II [AT.sub.1] receptors were similar on normal salt, but high salt increased [D.sub.5]R only in C57B1/6J. GRK4 expression was lower on normal but higher on high salt in C57Bl/6J than in SJL/J mice. Salt increased the excretion of microalbumin and 8-isoprostane (oxidative stress marker) and the degree of renal injury to a greater extent in SJL/J than in C57Bl/6J mice. A [D.sub.1]-like receptor agonist increased sodium excretion whereas a [D.sub.1]-like receptor antagonist decreased sodium excretion in SJL/J but not in C57B1/6J mice. In contrast, parathyroid hormone had a similar natriuretic effect in both strains. These results show that defective [D.sub.1]-like receptor function is a major cause of salt sensitivity in C57B1/6J mice, decreased renal dopamine production might also contribute. The relative resistance to renal injury of C57Bl/6J may be a consequence of decreased production of reactive oxygen species. angiotensin II receptors; dopamine receptors; GRK4; reactive oxygen species doi: 10.1152/ajpregu.00147.2009

Hypertension is a multigenic disorder in which abnormal counterregulation between dopamine and Ang II plays a role. Recent studies suggest that this counterregulation results, at least in part, from regulation of the expression of both the antihypertensive dopamine 5 receptor ([D.sub.5]R) and the prohypertensive Ang II type 1 receptor ([AT.sub.1]R). In this report, we investigated the in vivo and in vitro interaction between these GPCRs. Disruption of the gene encoding [D.sub.5]R in mice increased both blood pressure and [AT.sub.1]R protein expression, and the increase in blood pressure was reversed by [AT.sub.1]R blockade. Activation of [D.sub.5]R increased the degradation of glycosylated [AT.sub.1]R in proteasomes in HEK cells and human renal proximal tubule cells heterologously and endogenously expressing human [AT.sub.1]R and [D.sub.5]R. Confocal microscopy, Forster/fluorescence resonance energy transfer microscopy, and fluorescence lifetime imaging microscopy revealed that activation of [D.sub.5]R initiated ubiquitination of the glycosylated [AT.sub.1]R at the plasma membrane. The regulated degradation of [AT.sub.1]R via a ubiquitin/proteasome pathway by activation of [D.sub.5]R provides what we believe to be a novel mechanism whereby blood pressure can be regulated by the interaction of 2 counterregulatory GPCRs. Our results therefore suggest that treatments for hypertension might be optimized by designing compounds that can target the [AT.sub.1]R and the [D.sub.5]R., Introduction Hypertension is associated with sodium retention caused by decreased renal sodium excretion, which is tightly regulated by both natriuretic and antinatriuretic hormones. Dopamine and Ang II are among those [...]

Dopamine plays an important role in the pathogenesis of hypertension by regulating epithelial sodium transport and by interacting with vasoactive hormones/humoral factors, such as aldosterone, angiotensin, catecholamines, endothelin, oxytocin, prolactin pro-opiomelancortin, reactive oxygen species, renin, and vasopressin. Dopamine receptors are classified into [D.sub.1]-like ([D.sub.1] and [D.sub.5]) and [D.sub.2]-1ike ([D.sub.2], [D.sub.3], and [D.sub.4]) subtypes based on their structure and pharmacology. In recent years, mice deficient in one or more of the five dopamine receptor subtypes have been generated, leading to a better understanding of the physiological role of each of the dopamine receptor subtypes. This review summarizes the results from studies of various dopamine receptor mutant mice on the role of individual dopamine receptor subtypes and their interactions with other G protein-coupled receptors in the regulation of blood pressure. knockout mice; dopamine receptor

G protein-coupled receptor (GPCR) kinases (GRKs) regulate the sensitivity of GPCRs, including dopamine receptors. The GRK4 locus is linked to, and some of its polymorphisms are associated with, human essential hypertension. Transgenic mice overexpressing human (h) GRK4[gamma] A142V on a mixed genetic background (C57BL/6J and SJL/J) have impaired renal Dl-dopamine receptor ([D.sub.1]R) function and increased blood pressure. We now report that hGRK4[gamma] A142V transgenic mice, in C57BL/6J background, are hypertensive and have higher blood pressures than hGRK4[gamma] wild-type transgenic and nontransgenic mice. The hypertensive phenotype is stable because blood pressures in transgenic founders and F6 offspring are similarly increased. To determine whether the hypertension is associated with increased production of reactive oxygen species (ROS), we measured renal NADPH oxidase (Nox2 and Nox4) and heme oxygenase (HO-1 and HO-2) protein expressions and urinary excretion of 8-isoprostane and compared the effect of Tempol on blood pressure in hGRK4[gamma] A142V transgenic mice and [D.sub.5]R knockout ([D.sub.5.sup.-/-]) mice in which hypertension is mediated by increased ROS. The expressions of Nox isoforms and HO-2 and the urinary excretion of 8-isoprostane were similar in hGRK4[gamma] A142V transgenic mice and their controls. HO-1 expression was increased in hGRK4[gamma] A142V relative to hGRK4[gamma] wild-type transgenic mice. In contrast with the hypotensive effect of Tempol in [D.sub.5.sup.-/-] mice, it had no effect in hGRK4[gamma] A142V transgenic mice. We conclude that the elevated blood pressure of hGRK4[gamma] A142V transgenic mice is due mainly to the effect of hGRK4[gamma] A142V transgene acting via [D.sub.1]R and increased ROS production is not a contributor. hGRK4 polymorphism; hypertension; reactive oxygen species; G protein-coupled receptor kinases doi:10.1152/ajpheart.00944.2006

We isolated a cDNA clone encoding the gerbil A[T.sub.2] receptor (gA[T.sub.2]) gene from a gerbil adrenal gland cDNA library. The full-length cDNA contains a 1,089-bp open reading frame encoding 363 amino acid residues with 90.9, 96.1, and 95.6% identity with the human (hA[T.sub.2]), rat (rA[T.sub.2]), and mouse A[T.sub.2] (mA[T.sub.2]) receptors, respectively. There are at least seven non-conserved amino acids in the N[H.sub.2]-terminal domain and in positions [Val.sup.196], [Val.sup.217], and [Met.sup.293], important for angiotensin (ANG) II but not for CGP-42112 binding. Displacement studies in adrenal sections revealed that affinity of the gA[T.sub.2] receptor was 10-20 times lower for ANG II, ANG III, and PD-123319 than was affinity of the rA[T.sub.2] receptor. The affinity of each receptor remained the same for CGP-42112. When transfected into COS-7 cells, the gA[T.sub.2] receptor shows affinity for ANG II that is three times lower than that shown by the hA[T.sub.2] receptor, whereas affinities for ANG III and the A[T.sub.2] receptor ligands CGP-42112 and PD-123319 were similar. Autoradiography in sections of the gerbil head showed higher binding in muscles, retina, skin, and molars at embryonic day 19 than at 1 wk of age. In situ hybridization and emulsion autoradiography revealed that at embryonic day 19 the gA[T.sub.2] receptor mRNA was highly localized to the base of the dental papilla of maxillary and mandibular molars. Our results suggest selective growth-related functions in late gestation and early postnatal periods for the gA[T.sub.2] receptor and provide an essential basis for future mutagenesis studies to further define structural requirements for agonist binding. adrenal gland; brain; CGP-42112; dental papilla

Stress reduces gastric blood flow and produces acute gastric mucosal lesions. We studied the role of angiotensin II in gastric blood flow and gastric ulceration during stress. Spontaneously hypertensive rats were pretreated for 14 days with the [AT.sub.1] receptor antagonist candesartan before cold-restraint stress. [AT.sub.1] receptors were localized in the endothelium of arteries in the gastric mucosa and in all gastric layers. [AT.sub.1] blockade increased gastric blood flow by 40-50%, prevented gastric ulcer formation by 70-80% after cold-restraint stress, reduced the increase in adrenomedullary epinephrine and tyrosine hydroxylase mRNA without preventing the stress-induced increase in adrenal corticosterone, decreased the stress-induced expression of TNF-[alpha] and that of the adhesion protein ICAM-1 in arterial endothelium, decreased the neutrophil infiltration in the gastric mucosa, and decreased the gastric content of [PGE.sub.2]. [AT.sub.1] receptor blockers prevent stress-induced ulcerations by a combination of gastric blood flow protection, decreased sympathoadrenal activation, and anti-inflammatory effects (with reduction in TNF-[alpha] and ICAM-1 expression leading to reduced neutrophil infiltration) while maintaining the protective glucocorticoid effects and [PGE.sub.2] release. Angiotensin II has a crucial role, through stimulation of [AT.sub.1] receptors, in the production and progression of stress-induced gastric injury, and [AT.sub.1] receptor antagonists could be of therapeutic benefit. gastric blood flow; prostaglandins; tumor necrosis factor