Biomedical subjects

T Inagami

Publications and source records attributed to T Inagami.

At least 37 records · Page 2Linked to original sources

PubMed1999

Intracellular signaling of angiotensin II-induced p70 S6 kinase phosphorylation at Ser(411) in vascular smooth muscle cells. Possible requirement of epidermal growth factor receptor, Ras, extracellular signal-regulated kinase, and Akt.

Activation of p70 S6 kinase (p70(S6K)) by growth factors requires multiple signal inputs involving phosphoinositide 3-kinase (PI3K), its effector Akt, and an unidentified kinase that phosphorylates Ser/Thr residues (Ser(411), Ser(418), Ser(424), and Thr(421)) clustered at its autoinhibitory domain. However, the mechanism by which G protein-coupled receptors activate p70(S6K) remains largely uncertain. By using vascular smooth muscle cells in which we have demonstrated Ras/extracellular signal-regulated kinase (ERK) activation through Ca(2+)-dependent, epidermal growth factor (EGF) receptor transactivation by G(q)-coupled angiotensin II (Ang II) receptor, we present a unique cross-talk required for Ser(411) phosphorylation of p70(S6K) by Ang II. Both p70(S6K) Ser(411) and Akt Ser(473) phosphorylation by Ang II appear to involve EGF receptor transactivation and were inhibited by dominant-negative Ras, whereas the phosphorylation of p70(S6K) and ERK but not Akt was sensitive to the MEK inhibitor. By contrast, the phosphorylation of p70(S6K) and Akt but not ERK was sensitive to PI3K inhibitors. Similar inhibitory pattern on these phosphorylation sites by EGF but not insulin was observed. Taken together with the inhibition of Ang II-induced p70(S6K) activation by dominant-negative Ras and the MEK inhibitor, we conclude that Ang II-initiated activation of p70(S6K) requires both ERK cascade and PI3K/Akt cascade that bifurcate at the point of EGF receptor-dependent Ras activation.

Angiotensin II↗

PubMed1999

Mechanotransduction of rat aortic vascular smooth muscle cells requires RhoA and intact actin filaments.

The growth-promoting effect of mechanical stress on vascular smooth muscle cells (VSMCs) has been implicated in the progress of vascular disease in hypertension. Extracellular signal-regulated kinases (ERKs) have been implicated in cellular responses, such as vascular remodeling, induced by mechanical stretch. However, it remains to be determined how mechanical stretch activates ERKs. The cytoskeleton seems the most likely candidate for force transmission into the interior of the cell. Therefore, we examined (1) whether the cytoskeleton involves mechanical stretch-induced signaling, (2) whether Rho is activated by stretch, and (3) whether Rho mediates the stretch-induced signaling in rat cultured VSMCs. Mechanical stretch activated ERKs, with a peak response observed at 20 minutes, followed by a significant increase in DNA synthesis. Treatment with the ERK kinase-1 inhibitor, PD98059, inhibited the stretch-induced increase in DNA synthesis. Cytochalasin D, which selectively disrupts the network of actin filaments, markedly inhibited stretch-induced ERK activation. In the control state, RhoA was observed predominantly in the cytosolic fraction, but it was translocated in part to the particulate fraction in response to mechanical stretch. Botulinum C3 exoenzyme, which inactivates Rho p21 (known to participate in the reorganization of the actin cytoskeleton), attenuated stretch-induced ERK activation. Inhibition of Rho kinase (p160ROCK) also suppressed stretch-induced ERK activation dose dependently. Our results suggest that mechanotransduction in VSMCs is dependent on intact actin filaments, that Rho is activated by stretch, and that Rho/p160ROCK mediates stretch-induced ERK activation and vascular hyperplasia.

ADP Ribose Transferases↗

PubMed1999

Epidermal growth factor receptor is indispensable for c-Fos expression and protein synthesis by angiotensin II.

We have reported that angiotensin II induces the epidermal growth factor (EGF) receptor transactivation leading to extracellular signal-regulated kinase (ERK) activation in rat vascular smooth muscle cells. Here, we report that the EGF receptor kinase inhibitor AG1478 and the ERK kinase inhibitor PD98059 markedly inhibited angiotensin II-induced c-Fos expression and protein synthesis but not c-Jun expression in these cells. These data suggest that the EGF receptor transactivation and subsequent ERK activation are indispensable for angiotensin II-mediated growth promotion of vascular smooth muscle cells providing a new mechanistic insight whereby angiotensin II contributes abnormal vascular remodeling.

Animals↗

PubMed1999

Sustained hypersensitivity to angiotensin II and its mechanism in mice lacking the subtype-2 (AT2) angiotensin receptor.

The vast majority of the known biological effects of the renin-angiotensin system are mediated by the type-1 (AT1) receptor, and the functions of the type-2 (AT2) receptor are largely unknown. We investigated the role of the AT2 receptor in the vascular and renal responses to physiological increases in angiotensin II (ANG II) in mice with targeted deletion of the AT2 receptor gene. Mice lacking the AT2 receptor (AT2-null mice) had slightly elevated systolic blood pressure (SBP) compared with that of wild-type (WT) control mice (P < 0.0001). In AT2-null mice, infusion of ANG II (4 pmol/kg/min) for 7 days produced a marked and sustained increase in SBP [from 116 +/- 0.5 to 208 +/- 1 mmHg (P < 0.0001) (1 mmHg = 133 Pa)] and reduction in urinary sodium excretion (UNaV) [from 0.6 +/- 0.01 to 0.05 +/- 0.002 mM/day (P < 0.0001)] whereas neither SBP nor UNaV changed in WT mice. AT2-null mice had low basal levels of renal interstitial fluid bradykinin (BK), and cyclic guanosine 3', 5'-monophosphate, an index of nitric oxide production, compared with WT mice. In WT mice, dietary sodium restriction or ANG II infusion increased renal interstitial fluid BK, and cyclic guanosine 3', 5'-monophosphate by approximately 4-fold (P < 0.0001) whereas no changes were observed in AT2-null mice. These results demonstrate that the AT2 receptor is necessary for normal physiological responses of BK and nitric oxide to ANG II. Absence of the AT2 receptor leads to vascular and renal hypersensitivity to ANG II, including sustained antinatriuresis and hypertension. These results strongly suggest that the AT2 receptor plays a counterregulatory protective role mediated via BK and nitric oxide against the antinatriuretic and pressor actions of ANG II.

Angiotensin II↗

PubMed1999

Communication between myocytes and fibroblasts in cardiac remodeling in angiotensin chimeric mice.

To characterize the mode of action of angiotensin II (Ang II) in cardiac remodeling, we generated chimeric mice that are made of both homozygous Ang II receptor type 1A gene (Agtr1a) null mutant cells and Agtr1a intact cells expressing the lacZ gene (ROSA26). Both Agtr1a null and intact myocytes and interstitial cells independently form areas that are randomly distributed throughout the heart. The distribution of ROSA26 cardiomyocytes overlaps completely with that of Ang II binding, indicating that the majority of Ang II receptors reside on cardiomyocytes. When Ang II (1 ng/g body weight/min) was infused for 2 weeks, mice developed mild to moderate hypertension. The proliferating cardiac fibroblasts identified by bromodeoxyuridine staining were present predominantly in the areas surrounded by Agtr1a intact cardiomyocytes. When control chimeric mice made of wild-type cells and ROSA26 cells (i.e., both carrying intact Agtr1a) were infused with Ang II, fibroblast proliferation was found equally in these cardiomyocyte types. When compared with Agtr1a null mutant chimeras, the control chimeras had more extensive cardiac fibrosis, most prominently in perivascular regions. Therefore, in response to Ang II, cardiac fibroblasts proliferate through both the local and systemic action of Ang II. Importantly, the former is determined by the Ang II receptor of neighboring cardiomyocytes, indicating that a communication between myocytes and fibroblasts plays an important role during Ang II-dependent cardiac remodeling.

Angiotensin II↗

PubMed1999

Fyn kinase-directed activation of SH2 domain-containing protein-tyrosine phosphatase SHP-2 by Gi protein-coupled receptors in Madin-Darby canine kidney cells.

SHP-2, an SH2 domain-containing protein-tyrosine phosphatase, plays an important role in receptor tyrosine kinase-regulated cell proliferation and differentiation. Little is known about the activation mechanisms and the participation of SHP-2 in the activity of G protein-coupled receptors lacking intrinsic tyrosine kinase activity. We show that the activity of SHP-2 (but not SHP-1) is specifically stimulated by the selective alpha2A-adrenergic receptor agonist UK14304 and by lysophosphatidic acid (LPA) in Madin-Darby canine kidney (MDCK) cells. UK14304 and LPA promote the tyrosine phosphorylation of SHP-2 and its association with Grb2. The agonist-induced direct interaction of Grb2 with SHP-2 is mediated by the SH2 domain of Grb2 and the tyrosine phosphorylation of SHP-2. Rapid activation of Src family kinase by UK14304 preceded the SHP-2 activation. Among the Src family members (Src, Fyn, Lck, Yes, and Lyn) present in MDCK cells, Fyn was the only one specifically associated with SHP-2, and the physical interaction between them, which requires the Src family kinase activity, was increased in response to the agonists. Pertussis toxin, PP1 (a selective Src family kinase inhibitor), or overexpression of a catalytically inactive mutant of Fyn blocked the UK14304- or LPA-stimulated activity of SHP-2, SHP-2 tyrosine phosphorylation, and SHP-2 association with Grb2. Therefore, we have demonstrated for the first time that the activation of SHP-2 by these Gi protein-coupled receptors requires Fyn kinase and that there is a specific physical interaction of Fyn kinase with SHP-2 in MDCK cells.

Adaptor Proteins, Signal Transducing↗

PubMed1999

Vascular response to angiotensin II is exaggerated through an upregulation of AT1 receptor in AT2 knockout mice.

Blood pressure is elevated and pressor response to angiotensin II (Ang II) is exaggerated in AT2 null mice. The purpose of the present study was to elucidate the mechanism for the increased responsiveness to Ang II in the mice. The contraction of aortic strips generated by Ang II was significantly greater in the AT2 gene-deleted mice than the control, which was completely abolished by AT1 antagonist losartan. The aortic content of AT1 receptor was significantly increased (P < 0.05, n = 5) in the AT2 null mice (212 +/- 58.2 fmol/mg protein) compared with the control (98.2 +/- 55.9 fmol/mg protein). While both AT1 and AT2 mRNAs were expressed in the aorta of the control mice, only AT1 mRNA was expressed in the AT2 knockout mice. The expression of AT1 mRNA in the AT2 knockout mice was significantly higher (1.5-fold, P < 0.05, n = 5) than that in the control. The present study clearly demonstrated that the increased vascular reactivity to Ang II in AT2 knockout mice is at least partly due to an increased vascular AT1 receptor expression and suggested that AT2 counteracts AT1-mediated vascular action of Ang II through downregulation of AT1 receptor by a crosstalk between these receptors by some as yet unknown mechanisms.

Aldosterone↗

PubMed1999

Cloning and characterization of a short variant of the corticotropin-releasing factor receptor subtype from rat amygdala.

We have identified and characterized a cDNA encoding a novel isoform of the corticotropin-releasing factor (CRF) receptor, referred to as CRF2alpha-tr, from the rat amygdala cDNA library. The nucleotide sequence of the cloned cDNA has a structure of an alternatively spliced form of the CRF2alpha receptor, which contains unspliced introns 6 and 7 in the message, and encodes a 236-amino-acid truncated protein that comprises three unique transmembrane domains. Northern blot analysis shows that the CRF2alpha-tr receptor is more strongly expressed in the rat amygdala, thalamus, and hypothalamus than the intact CRF2alpha receptor. Western blot analysis also reveals that the CRF2alpha-tr protein can be expressed in transfected COS-7 cells as well as CRF2alpha. Furthermore, this receptor binds rat/human CRF with almost the same low affinity (Kd = 12.7 nM) as the CRF2alpha and without accumulation of intracellular cAMP. Interestingly, it does not bind sauvagine or rat urocortin. These findings suggest that this truncated CRF receptor is the major isoform of CRF2alpha receptor mRNA transcripts in the amygdala and would mediate some functions of CRF pathways in the central nervous system.

Alternative Splicing↗

PubMed1999

Effects of targeted disruption of the mouse angiotensin II type 2 receptor gene on stress-induced hyperthermia.

1. We have previously reported that brain angiotensin II type 2 receptors (AT2) contribute to immunological stress-induced hyperthermia (fever) in rats. Now, in mice, we report the effect of AT2 gene disruption on the hyperthermia induced by immunological (interleukin-1 (IL-1) injection) and non-immunological (saline injection or cage switch) stress. 2. AT2-deficient and control mice both showed typical circadian rhythmicity in body temperature and physical activity. During the latter half of the dark period, AT2-deficient mice exhibited a lower body temperature than the controls. 3. By comparison with the controls, AT2-deficient mice exhibited: (i) a significantly smaller hyperthermia after intraperitoneal (i.p.) injection of IL-1beta; (ii) significantly greater increases in body temperature and physical activity after i. p. saline; and (iii) a significantly greater hyperthermia (but a similar increase in activity) during cage-switch stress. 4. These results suggest that AT2, presumably in the brain, plays important roles in stress-induced hyperthermia in mice.

Animals↗

PubMed1999

Anxiety-like behavior in mice lacking the angiotensin II type-2 receptor.

The main biological role of angiotensin II type 2 receptor (AT2) has not been established. We made use of targeted disruption of the mouse AT2 gene to examine the role of the AT2 receptor in the central nervous system (CNS). AT2-deficient mice displayed anxiety-like behavior compared with wild-type mice. However, AT2-deficient mice showed no depressant-like activity and no change in hexobarbital-induced sleeping time as compared with findings in wild-type mice. Both noradrenergic and corticotropin-releasing factor (CRF) neuronal systems appear to be involved in this anxiety-like behavior. Diazepam, captopril (angiotensin I converting enzyme inhibitor), prazosin (alpha1 antagonist) reversed the anxiety-like behavior in these AT2-deficient mice, whereas yohimbine (alpha2 antagonist), phenylephrine (alpha1 agonist), clonidine (alpha2 agonist), isoproterenol (beta1/beta2 agonist), propranolol (beta1/beta2 antagonist) and alpha-helical CRF9-41 (CRF receptor antagonist) has no apparent effects on anxiety-like behavior in AT2-deficient mice. In addition, concentrations of plasma adrenocorticotropic hormone (ACTH) and corticosterone in AT2-deficient mice did not differ from these in wild-type mice, hence, there are probably no endocrine abnormalities involving the hypothalamic-pituitary-adrenal axis (HPA). The amygdala appears to play an important role in many of the responses to fear and anxiety. The number of [3H]prazosin but not [125I]CRF binding sites in the amygdala was significantly reduced in AT2-deficient mice. These findings indicate that the noradrenergic system is involved in mediating the anxiety-like behavior in AT2-deficient mice.

Adrenocorticotropic Hormone↗

PubMed1999

Role of the angiotensin type 2 receptor gene in congenital anomalies of the kidney and urinary tract, CAKUT, of mice and men.

Angiotensin type 2 receptor gene null mutant mice display congenital anomalies of the kidney and urinary tract (CAKUT). Various features of mouse CAKUT impressively mimic human CAKUT. Studies of the human type 2 receptor (AGTR2) gene in two independent cohorts found that a significant association exists between CAKUT and a nucleotide transition within the lariat branchpoint motif of intron 1, which perturbs AGTR2 mRNA splicing efficiency. AGTR2, therefore, has a significant ontogenic role for the kidney and urinary tract system. Studies revealed that the establishment of CAKUT is preceded by delayed apoptosis of undifferentiated mesenchymal cells surrounding the urinary tract during key ontogenic events, from the ureteral budding to the expansive growth of the kidney and ureter.

Animals↗

PubMed1999

Angiotensin receptors: molecular biology and signalling.

1. The active peptide hormone angiotensin II (AngII) is formed from its prohormone angiotensinogen by way of inactive angiotensin I. The highly specific protease, renin, responsible for the initiation of this system was elusive and considered unstable. We isolated it in a pure and stable form from the kidney of the pig, human, rat, and land submandibular glands of the mouse. It was shown that there is only one type of renin with highly stringent substrate specificity, except certain strains of the mouse which have two gene products. 2. The well-known diversity of action of AngII can be attributed to the presence of more than two subtypes, AT1 and AT2, as well as multiple signalling pathways for both of them. 3. The first subtype AT1 was shown to mediate most of the traditionally recognized AngII functions such as vasoconstriction, electrolyte homeostasis etc. 4. Although the identification of the signalling modes of the second subtype AT2 still remains elusive, we and others have shown evidence that its action is generally antagonistic to that of AT1. AT2 inhibits AT1 (growth factor-stimulated cell growth), AT2 attenuates the vasoconstriction induced by AT1. Since AT2 seems to mediate nitric oxide formation in the renal cells, it may initiate a natriuretic pathway in contrast to the sodium-retaining action of AT1-mediated AngII action. 5. Newer mechanisms and functions of these and other receptors will be clarified by the combination of molecular, cellular and integrated physiological studies.

Amino Acid Sequence↗

PubMed1999

Potent antihypertrophic effect of the bradykinin B2 receptor system on the renal vasculature.

BACKGROUND: Angiotensin type 1 (AT1) receptor-deficient mice (Agtr1-/-), which selectively lack both AT1A and AT1B receptor genes, are characterized by marked intrarenal vascular thickening. In the present study, we explored the possible involvement of the kinin-kallikrein system in the development of this renal vascular hypertrophy. METHODS: Wild-type and Agtr1-/- mice were examined for the developmental regulation pattern of the kinin-kallikrein system and treated with aprotinin (a kallikrein inhibitor), AcLys [D-b Nal7, Ile8] des-Arg9-bradykinin (a bradykinin B1 receptor antagonist), or Hoe-140 (a bradykinin B2 receptor antagonist) from 3 to 14 days of age. RESULTS: The normal postnatal up-regulation of kininase II was organ-specifically suppressed in Agtr1-/- kidneys at 2 and 3 weeks of age. Immunohistochemical staining in Agtr1-/- mice revealed tissue kallikrein staining along the nephron from connecting tubules to cortical collecting tubules in proximity to the hypertrophic vasculature, whereas tissue kallikrein staining was confined to connecting tubules in wild-type mice. Aprotinin and Hoe-140 accelerated the vascular hypertrophy significantly as determined by wall thickness ratio, whereas B1 receptor antagonism had no effect. CONCLUSION: The kinin-kallikrein system in the Agtr1-/- mouse kidney is functionally activated by local suppression of kininase II and extensive redistribution of kallikrein to perivascular areas. This activation, specific to the kidney, serves to dampen a development of the marked vascular hypertrophy. These results demonstrate, to our knowledge for the first time, the antihypertrophic effect of the bradykinin B2 receptor system on the renal vasculature in vivo.

Animals↗

PubMed1999

Angiotensin II type 1 receptor expression in two cases of juxtaglomerular cell tumor: correlation to negative feedback of renin secretion by angiotensin II.

The angiotensin II (Ang II) type 1 (AT1) receptor is highly expressed on juxtaglomerular (G) cells and is assumed to be involved in the negative short loop feedback regulation of renin secretion and in the suppression of Ang II-mediated JG cell proliferation and/or growth. However, as JG cell tumor is rare, expression and pathophysiological significance of AT1 receptor expression in JG cell tumor remain unknown. In the present study, we investigated renin responses to various treatments, including the angiotensin converting enzyme inhibitor captopril, and correlated the results with AT1 and Ang II type 2 (AT2) receptor mRNA expression levels in two cases of JG cell tumor. Whereas plasma renin activity (PRA) did not show any significant change in Case 1, it was increased by 72% in Case 2 in response to captopril challenge. In concordance with these results, AT1 receptor mRNA was not detected in tumor tissue of Case 1 but was clearly demonstrated in the tumor of Case 2. AT2 receptor mRNA expression was not detected in either of the cases. In contrast to captopril challenge, PRA was suppressed by 30% in Case 1 and 42% in Case 2 in response to saline infusion, and was increased by 230% in Case 1 and 59% in Case 2 in response to furosemide-upright posture for 2 h. These results suggest that the short loop feedback inhibition of renin secretion by Ang II in JG cell tumor is closely related to AT1 receptor expression levels in the tumor tissue. In addition, the result suggested that despite its autonomy, renin secretion from JG cell tumor is still under physiological regulatory control.

Adenocarcinoma↗

PubMed1999

Involvement of PYK2 in angiotensin II signaling of vascular smooth muscle cells.

-PYK2, a recently identified Ca2+-sensitive tyrosine kinase, has been implicated in extracellular signal-regulated kinase (ERK) activation via several G protein-coupled receptors. We have reported that angiotensin II (Ang II) induces Ca2+-dependent transactivation of the epidermal growth factor receptor (EGFR) which serves as a scaffold for preactivated c-Src and downstream adaptors (Shc/Grb2), leading to ERK activation in cultured rat vascular smooth muscle cells (VSMC). Herein we demonstrate the involvement of PYK2 in this cascade. Ang II rapidly induced tyrosine phosphorylation of PYK2, whose effect was completely inhibited by an AT1 receptor antagonist and an intracellular Ca2+ chelator. A Ca2+ ionophore also induced PYK2 tyrosine phosphorylation to a level comparable with that by Ang II, whereas phorbol ester-induced phosphorylation was less than that by Ang II. Moreover, PYK2 formed a complex coprecipitable with catalytically active c-Src after Ang II stimulation. Although a selective EGFR kinase inhibitor completely abolished Ang II-induced recruitment of Grb2 to EGFR and markedly attenuated Ang II-induced ERK activation, it had no effect on Ang II-induced PYK2 tyrosine phosphorylation or its association with c-Src and Grb2. These data suggest that the AT1 receptor uses Ca2+-dependent PYK2 to activate c-Src, thereby leading to EGFR transactivation, which preponderantly recruits Grb2 in rat VSMC.

Angiotensin II↗

PubMed1999

Intracellular sodium modulates the expression of angiotensin II subtype 2 receptor in PC12W cells.

Although the angiotensin II subtype 2 receptor (AT2-R) is expressed abundantly in the adrenal medulla, its physiological significance has not yet been determined. To obtain fundamental knowledge of the regulation of AT2-R expression in the adrenal medulla, we investigated the effects of modulating several ion channels on AT2-R expression in PC12W cells. Experiments were performed after 24 hours of serum depletion under subconfluent conditions. After 48 hours of treatment with various agonists or antagonists, the receptor density and mRNA level of AT2-Rs were quantified by 125I-[Sar1, Ile8]angiotensin II binding and Northern blot analysis. Ouabain (10 to 100 nmol/L) and insulin (10 to 100 nmol/L) dose-dependently increased receptor density and mRNA level. Analysis of the binding characteristics revealed that the ouabain-dependent increase in AT2-R levels was due to an increase in binding capacity without a change in the Kd value. These increases were blocked by lowering the Na+ concentration in the medium. A low concentration of the sodium ionophore monensin (10 nmol/L), the K+-channel blocker quinidine (10 micromol/L), and the ATP-sensitive K+-channel blockers tolbutamide (100 micromol/L) and glybenclamide (10 micromol/L) also significantly increased receptor density, but the ATP-sensitive K+-channel agonist cromakalim (100 micromol/L) decreased receptor density significantly (P<0.01). Nifedipine (10 micromol/L) decreased basal receptor density and completely blocked the increase in receptor density caused by these agents. The increase in receptor density caused by an increase in intracellular Na+ was accompanied by an increase in mRNA level, whereas the ATP-sensitive K+-channel blockers did not change mRNA level. Nifedipine slightly decreased mRNA level. These results suggest that AT2-R expression is sensitively regulated by intracellular cation levels. The change in intracellular Na+ level transcriptionally regulates AT2-R expression, whereas the K+-channel blocker-dependent upregulation appears to be at least in part posttranslational.

Angiotensin II↗

PubMed1999

Elements of a paracrine tubular renin-angiotensin system along the entire nephron.

The renin-angiotensin system is a major regulator of body sodium, predominantly through the actions of intrarenal angiotensin II of unclear origin. We show that polarized epithelium of the proximal tubule synthesizes and secretes angiotensinogen at its apical side and that the protein can be detected in urine as a function of dietary sodium. Furthermore, we demonstrate that renin is expressed and secreted in a restricted nephron segment, the connecting tubule, also in a sodium-dependent fashion. A paracrine renin-angiotensin system operating along the entire nephron may contribute to long-term arterial pressure regulation by integrating distant tubular sodium-reabsorbing functions.

Angiotensinogen↗

PubMed1999

Increased renal vasodilator prostanoids prevent hypertension in mice lacking the angiotensin subtype-2 receptor.

The angiotensin subtype-1 (AT(1)) receptor mediates renal prostaglandin E(2) (PGE(2)) production, and pharmacological blockade of the angiotensin subtype-2 (AT(2)) receptor potentiates the action of angiotensin II (Ang II) to increase PGE(2) levels. We investigated the role of the AT(2) receptor in prostaglandin metabolism in mice with targeted deletion of the AT(2) receptor gene. Mice lacking the AT(2) receptor (AT(2)-null) had normal blood pressure that was slightly elevated compared with that of wild-type (WT) control mice. AT(2)-null mice had higher renal interstitial fluid (RIF) 6-keto-PGF(1alpha) (a stable hydrolysis product of prostacyclin [PGI(2)]) and PGE(2) levels than did WT mice, and had similar increases in PGE(2) and 6-keto-PGF(1alpha) in response to dietary sodium restriction and Ang II infusion. In contrast, AT(2)-null mice had lower PGF(2alpha) levels compared with WT mice during basal conditions and in response to dietary sodium restriction or infusion of Ang II. RIF cAMP was markedly higher in AT(2)-null mice than in WT mice, both during basal conditions and during sodium restriction or Ang II infusion. AT(1) receptor blockade with losartan decreased PGE(2), PGI(2), and cAMP to levels observed in WT mice. To determine whether increased vasodilator prostanoids prevented hypertension in AT(2)-null mice, we treated AT(2)-null and WT mice with indomethacin for 14 days. PGI(2), PGE(2), and cAMP were markedly decreased in both WT and AT(2)-null mice. Blood pressure increased to hypertensive levels in AT(2)-null mice but was unchanged in WT. These results demonstrate that in the absence of the AT(2) receptor, increased vasodilator prostanoids protect against the development of hypertension.

Angiotensin II↗