Inhibition of Inward Rectifier K+ Currents by Angiotensin II in Rat Atrial Myocytes: Lack of Effects in Cells from Spontaneously Hypertensive Rats

We examined the effects of angiotensin II (Ang II) on inward rectifier K+ currents (IK1) in rat atrial myocytes. [125I]Ang II-binding assays revealed the presence of both Ang II type 1 (AT1) and type 2 (AT2) receptors in atrial membrane preparations. Ang II inhibited IK1 in isolated atrial myocytes with an IC50 of 46 nmol/l. This inhibition was abolished by the AT, antagonist RNH6270 but not at all by the AT2 antagonist PD123319. Treatment of cells with pertussis toxin or a synthetic decapeptide corresponding to the carboxyl-terminus of Gialpha-3 abolished the inhibition by Ang II, indicating the role of a Gi-dependent signaling pathway. Accordingly, Ang II failed to inhibit IK1 in the presence of forskolin, dibutyryl-cAMP or protein kinase A catalytic subunits. In spite of the increased binding capacities for [125I]Ang II, Ang II failed to affect IKI in cells from spontaneously hypertensive rats (SHR). AT, immunoprecipitation from atrial extracts revealed decreased amounts of Gialpha-2 and Gialpha-3 proteins associated with this receptor in SHR as compared with controls. The reduced coupling of AT, with Gialpha. proteins may underlie the unresponsiveness of atrial IK1 to Ang II in SHR cells.

Deletion of Angiotensin II Type 2 Receptor Exaggerated Atherosclerosis in Apolipoprotein E–Null Mice

Background— The role of angiotensin II (Ang II) type 2 (AT 2 ) receptor in atherosclerosis was explored with the use of AT 2 receptor/apolipoprotein E (ApoE)–double-knockout (AT 2 /ApoE-DKO) mice, with a focus on oxidative stress.

Methods and Results— After treatment with a high-cholesterol diet (1.25% cholesterol) for 10 weeks, ApoE-knockout (KO) mice developed atherosclerotic lesions in the aorta. In AT 2 /ApoE-DKO mice receiving a high-cholesterol diet, the atherosclerotic changes were further exaggerated, without significant changes in plasma cholesterol level and blood pressure. In the atherosclerotic lesion, an increase in superoxide production, NADPH oxidase activity, and expression of p47 phox was observed. These changes were also greater in AT 2 /ApoE-DKO mice. An Ang II type 1 (AT 1 ) receptor blocker, valsartan, inhibited atherosclerotic lesion formation, superoxide production, NADPH oxidase activity, and p47 phox expression; these inhibitory effects were significantly weaker in AT 2 /ApoE-KO mice. We further examined the signaling mechanism of the AT 2 receptor–mediated antioxidative effect in cultured fetal vascular smooth muscle cells. NADPH oxidase activity and phosphorylation and translocation of p47 phox induced by Ang II were inhibited by valsartan but enhanced by an AT 2 receptor blocker, PD123319.

Conclusions— These results suggest that AT 2 receptor stimulation attenuates atherosclerosis through inhibition of oxidative stress and that the antiatherosclerotic effect of valsartan could be at least partly due to AT 2 receptor stimulation by unbound Ang II.

Sex Difference in Vascular Injury and the Vasoprotective Effect of Valsartan Are Related to Differential AT 2 Receptor Expression

The angiotensin II type 2 (AT2) receptor is upregulated in pathological conditions such as vascular injury and exerts antagonistic effects against AT1 receptor-mediated actions. We examined the possibility that the sex difference in vascular remodeling is associated with altered AT2 receptor expression, which is located on the X chromosome. In this study, we examined this possibility by using AT2 receptor-null (Agtr2-) mice. Vascular injury was induced by polyethylene cuff placement around the femoral artery of wild-type (Agtr2+) and Agtr2- mice. In Agtr2+ mice, AT2 receptor expression in the injured artery was enhanced, and this increase was greater in female than in male mice, with no significant difference in AT1 receptor expression between male and female mice. Increases in neointimal formation, DNA synthesis, expression of monocyte chemoattractant protein-1, production of superoxide anion, and NADPH oxidase activity in the injured artery were attenuated in female compared with male mice. These parameters were augmented in Agtr2- mice, whereas the sex differences in these parameters were smaller in Agtr2- than in Agtr2+ mice. Treatment with a nonhypotensive dose of the AT1 receptor blocker valsartan decreased these parameters significantly in Agtr2+ mice, and these inhibitory effects of valsartan were greater in female mice. This sex difference in valsartan's inhibitory effect was less marked in Agtr2- mice. Our results suggest that the sex difference in response to vascular injury could be at least partially attributed to the exaggerated AT2 receptor expression in the injured vessel in female mice.

Aldosterone and angiotensin II synergistically induce mitogenic response in vascular smooth muscle cells

Interaction between aldosterone (Aldo) and angiotensin II (Ang II) in the cardiovascular system has been highlighted; however, its detailed signaling mechanism is poorly understood. Here, we examined the cross-talk of growth-promoting signaling between Aldo and Ang II in vascular smooth muscle cells (VSMC). Treatment with a lower dose of Aldo (10(-12) mol/L) and with a lower dose of Ang II (10(-10) mol/L) significantly enhanced DNA synthesis, whereas Aldo or Ang II alone at these doses did not affect VSMC proliferation. This effect of a combination of Aldo and Ang II was markedly inhibited by a selective AT1 receptor blocker, olmesartan, a mineralocorticoid receptor antagonist, spironolactone, an MEK inhibitor, PD98059, or an EGF receptor tyrosine kinase inhibitor, AG1478. Treatment with Aldo together with Ang II, even at noneffective doses, respectively, synergistically increased extracellular signal-regulated kinase (ERK) activation, reaching 2 peaks at 10 to 15 minutes and 2 to 4 hours. The early ERK peak was effectively blocked by olmesartan or an EGF receptor kinase inhibitor, AG1478, but not by spironolactone, whereas the late ERK peak was completely inhibited by not only olmesartan, but also spironolactone. Combined treatment with Aldo and Ang II attenuated mitogen-activated protein kinase phosphatase-1 (MKP-1) expression and increased Ki-ras2A expression. The late ERK peak was not observed in VSMC treated with Ki-ras2A-siRNA. Interestingly, the decrease in MKP-1 expression and the increase in Ki-ras2A expression were restored by PD98059 or AG1478. These results suggest that Aldo exerts a synergistic mitogenic effect with Ang II and support the notion that blockade of both Aldo and Ang II could be more effective to prevent vascular remodeling.

Attenuation of diet-induced weight gain and adiposity through increased energy expenditure in mice lacking angiotensin II type 1a receptor

Given that angiotensin II (AII) type 1 and 2 receptors (Agtr1 and Agtr2) are expressed in adipose tissue, AII may act directly on adipose tissue. However, regardless of whether AII directly modulates adipose tissue growth and metabolism in vivo and, if so, whether it is mediated via Agtr1 are still matters of debate. To understand the functional role of Agtr1 in adipose tissue growth and metabolism in vivo, we examined the metabolic phenotypes of mice lacking Agtr1a (Agtr1a-/- mice) during a high-fat diet. The Agtr1a-/- mice exhibited the attenuation of diet-induced body weight gain and adiposity, and insulin resistance relative to wild-type littermates (Agtr1a+/+ mice). They also showed increased energy expenditure accompanied by sympathetic activation, as revealed by increased rectal temperature and oxygen consumption, increased expression of uncoupling protein-1 mRNA in brown adipose tissue, and increased urinary catecholamine excretion. The heterozygous Agtr1a-deficient mice (Agtr1a+/- mice) also exhibited metabolic phenotypes similar to those of Agtr1a-/- mice. Using mouse embryonic fibroblasts derived from Agtr1a+/+ and Agtr1a-/- mice, we found no significant difference between genotypes in the ability to differentiate into lipid-laden mature adipocytes. In primary cultures of mouse mature adipocytes, AII increased the expression of mRNAs for some adipocytokines, which was abolished by pharmacological blockade of Agtr1. This study demonstrates that Agtr1a-/- mice exhibit attenuation of diet-induced weight gain and adiposity through increased energy expenditure. The data also suggest that AII does not affect directly adipocyte differentiation, but can modulate adipocytokine production via Agtr1.

Chemosensitivity testing of ovarian cancer using the histoculture drug response assay: sensitivity to cisplatin and clinical response

Despite cytoreductive surgery and chemotherapy, the prognosis of advanced ovarian cancer is still poor. Predicting the chemosensitivity of tumors might improve the outcome. Therefore, we investigated the clinical value of the histoculture drug response assay for ovarian cancer. Tumor specimens were cultured for 7 days on collagen gel sponge in medium containing cisplatin, and the 50% inhibitory concentration was determined by the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyltetrazolium bromide assay. Then the in vitro sensitivity to cisplatin was compared with the clinical response and survival. Apoptosis of tumor cells was also investigated. Among 173 ovarian cancer patients, 164 were evaluable by the assay, and 29 patients had measurable lesions for which the clinical response could be determined. The 5-year survival rate was significantly higher in patients with chemosensitive tumors than in those with chemoresistant tumors when the cutoff value was set at a 50% inhibitory concentration of 25 microg/mL and the accuracy of the assay was 82.8% (24/29). As chemosensitivity to cisplatin became greater, the number of apoptotic cells also increased. This chemosensitivity assay may help predict the clinical response to cisplatin-based chemotherapy, thus improving the survival of ovarian cancer patients.

Effect of combination of calcium antagonist, azelnidipine, and AT1 receptor blocker, olmesartan, on atherosclerosis in apolipoprotein E-deficient mice

OBJECTIVE

Angiotensin II type 1 receptor blockers (ARB) are widely recognized to have a vasculoprotective effect. Accumulating data have revealed that calcium antagonists also retard atherosclerosis. We examined the possibility that combination therapy of ARB and calcium antagonists could more effectively prevent atherosclerosis than monotherapy.

METHODS AND RESULTS

We observed a marked increase in the atherosclerotic area, associated with the exaggerated expression of nicotinamide adenine dinucleotide (phosphate), reduced form [NAD(P)H] oxidase subunits (p22 and p47) and superoxide anion production, in the aorta of apolipoprotein E-deficient mice maintained on a 1.25% high-cholesterol diet for 10 weeks. A calcium antagonist, azelnidipine, at a dose of 1 mg/kg a day or an ARB, olmesartan, at a dose of 3 mg/kg a day, significantly inhibited these parameters, with no change in systolic blood pressure and the blood cholesterol level. Moreover, the co-administration of lower doses of azelnidipine (0.1 mg/kg a day) and olmesartan (1 mg/kg a day) significantly inhibited the atherosclerotic area and oxidative stress, whereas azelnidipine or olmesartan alone at these doses did not affect these parameters. Furthermore, we observed similar inhibitory effects of azelnidipine or olmesartan on angiotensin II-induced NADPH oxidase activity and Akt activity in cultured vascular smooth muscle cells.

CONCLUSION

These results suggest that the co-administration of calcium antagonists and ARB synergistically blunts oxidative stress at least partly through the inhibition of Akt activity and enhances the beneficial effects of these drugs on atherosclerosis compared with monotherapy.

Renin-Angiotensin System Modulates Oxidative Stress–Induced Endothelial Cell Apoptosis in Rats

The role of the renin-angiotensin system in oxidative stress–induced apoptosis of endothelial cells (ECs) was investigated using a rat model and cultured ECs. EC apoptosis was induced by 5-minute intra-arterial treatment of a rat carotid artery with 0.01 mmol/L H 2 O 2 and was evaluated at 24 hours by chromatin staining of en face specimens with Hoechst 33342. Although activity of angiotensin-converting enzyme in arterial homogenates was not increased, administration of an angiotensin-converting enzyme inhibitor temocapril for 3 days before H 2 O 2 treatment inhibited EC apoptosis, followed by reduced neointimal formation 2 weeks later. Also, an angiotensin II type 1 (AT1) receptor blocker (olmesartan) inhibited EC apoptosis, whereas angiotensin II administration accelerated apoptosis independently of blood pressure. Next, cultured ECs derived from a bovine carotid artery were treated with H 2 O 2 to induce apoptosis, as evaluated by DNA fragmentation. Combination of angiotensin II and H 2 O 2 dose-dependently increased EC apoptosis and 8-isoprostane formation, a marker of oxidative stress. Conversely, temocapril and olmesartan reduced apoptosis and 8-isoprostane formation induced by H 2 O 2 , suggesting that endogenous angiotensin II interacts with H 2 O 2 to elevate oxidative stress levels and EC apoptosis. Neither an AT2 receptor blocker, PD123319, affected H 2 O 2 -induced apoptosis, nor a NO synthase inhibitor, N G -nitro- l -arginine methyl ester, influenced the effect of temocapril on apoptosis in cell culture experiments. These results suggest that AT1 receptor signaling augments EC apoptosis in the process of oxidative stress–induced vascular injury.

Bovine Posterior Pituitary Extract Stimulates Prolactin Release from the Anterior Pituitary Gland In Vitro and In Vivo in Cattle

It has been reported that the posterior pituitary (PP) gland contains a potent, unknown prolactin (PRL)-releasing factor (PRF) in rats. PRFs are assumed to be produced in neurones located within the hypothalamus, and to be peptidergic in nature. However, little is known about PRFs in domestic animals. To characterize the PRF in the PP of domestic animals, the present study examined the PRL-releasing activity of an acidic extract from bovine PP (bPP) in vitro and in vivo in cattle. First, the PRL-releasing effect of bPP extract was compared with that of PRL-releasing peptide (PrRP), and thyrotropin-releasing hormone (TRH) from cultured bovine anterior pituitary cells. The extract significantly increased PRL concentrations in the culture medium, at doses of 0.002 and 0.02 eq./ml (one eq. is the PP extract from one animal), compared with the control (p < 0.05). PrRP failed to stimulate the release of PRL. TRH significantly increased PRL concentrations in the culture medium, at doses from 10(-9) to 10(-7) M, compared with the control (p < 0.05). The rate of increase in the PRL concentration, by 0.02 eq./ml bPP extract, was significantly greater than that in TRH (p < 0.05). Secondly, plasma PRL responses to the intravenous (i.v.) injection of bPP extract (0.5 eq./head), PrRP [3.59 mug/kg body weight (BW)], TRH (1 mug/kg BW), and a dopamine receptor antagonist (sulpiride, 0.1 mg/kg BW), were examined in calves. PrRP failed to stimulate PRL release; however, plasma PRL increased immediately following the injection of bPP extract, TRH and sulpiride. The PRL-releasing effect of i.v. injections of TRH and sulpiride was more potent than that of bPP extract. Finally, plasma PRL responses to the intra-hypothalamic injection of bPP extract were examined in calves. The intra-hypothalamic infusion (arcuate nucleus) of 0.0625 eq./head of bPP extract strongly stimulated PRL release in calves (p < 0.05). The present results show that PP contains a physiologically potent PRF in cattle.

Inhibitory effects of AT1 receptor blocker, olmesartan, and estrogen on atherosclerosis via anti-oxidative stress

The present study explored the possibility that estrogen enhances the inhibitory effect of an angiotensin II type-1 (AT1) receptor blocker (ARB), olmesartan, on atherosclerosis, focusing on oxidative stress using apolipoprotein E knockout mice (ApoEKO). After 6 weeks on a high-cholesterol diet, marked atherosclerotic lesion formation with an increase in oxidative stress, such as superoxide production, NAD(P)H oxidase activity and expression of p47phox mRNA and rac-1 mRNA, were observed in the proximal aorta in both male and female ApoEKO mice, whereas these changes were less marked in female mice. Ovariectomy enhanced these parameters, the changes of which were reversed by 17beta-estradiol (80 microg/kg per day) replacement. Treatment with olmesartan (3 mg/kg per day) significantly inhibited oxidative stress and atherosclerosis, whereas its inhibitory effects were more marked in female than in male or ovariectomized mice. Smaller doses of olmesartan (0.5 mg/kg per day) or 17beta-estradiol (20 microg/kg per day) did not influence atherosclerosis and oxidative stress in ovariectomized mice, whereas co-administration of olmesartan and 17beta-estradiol at these doses attenuated these parameters. An angiotensin-converting enzyme (ACE) inhibitor, temocapril, also inhibited atherosclerotic changes similarly to olmesartan. Moreover, angiotensin II-mediated activation of NAD(P)H oxidase in cultured vascular smooth muscle cells was attenuated by 17beta-estradiol. These results indicate that estrogen and an ARB synergistically attenuate atherosclerosis at least partly via inhibition of oxidative stress.

The novel angiotensin II type 1 receptor (AT1R)-associated protein ATRAP downregulates AT1R and ameliorates cardiomyocyte hypertrophy

Activation of angiotensin II (Ang II) type 1 receptor (AT1R) signaling is reported to play an important role in cardiac hypertrophy. We previously cloned a novel molecule interacting with the AT1R, which we named ATRAP (for Ang II type 1 receptor-associated protein). Here, we report that overexpression of ATRAP significantly decreases the number of AT1R on the surface of cardiomyocytes, and also decreases the degree of p38 mitogen-activated protein kinase phosphorylation, the activity of the c-fos promoter and protein synthesis upon Ang II treatment. These results indicate that ATRAP significantly promotes downregulation of the AT1R and further attenuates certain Ang II-mediated hypertrophic responses in cardiomyocytes.

Effect of Azelnidipine on Angiotensin II-Mediated Growth-Promoting Signaling in Vascular Smooth Muscle Cells

The detailed mechanism of the effects of extracellular Ca2+ entry blockade on angiotensin II (Ang II) type 1 (AT1) receptor-mediated growth-promoting signals in vascular smooth muscle cells (VSMCs) is not fully understood. Ang II stimulation caused biphasic activation of growth-promoting signals, reaching a peak at 5 to 10 min followed by a decrease and a second peak at around 2 to 4 h. Addition of PD98059 (2'-amino-3'-methoxyflavone), a mitogen-activated protein kinase/extracellular signal-regulated kinase kinase inhibitor, or AG490 [alpha-cyano-(3,4-dihydroxy)-N-benzylcinnamide], a Janus-activated kinase 2 (Jak2) inhibitor, even 4 h after Ang II treatment inhibited [3H]thymidine incorporation. The calcium channel blocker azelnidipine attenuated the later peaks of extracellular signal-regulated kinase (ERK), tyrosine kinase 2, Jak2 activation, and phosphorylation of signal transducer and activator of transcription (STAT)1 and STAT3. Interestingly, azelnidipine increased rather than decreased the later ERK peaks in cells treated with small interfering RNA against mitogen-activated protein kinase phosphatase-1. Ang II-mediated [3H]thymidine incorporation was inhibited dose dependently by azelnidipine and also by azelnidipine, plus olmesartan, whereas olmesartan or azelnidipine alone at such lower doses did not affect [3H]thymidine incorporation. These data provide new insight into the manner in which calcium channels exert an essential action in the AT1 receptor-mediated growth-promoting actions in VSMCs.

Relationship between maximal oxygen uptake and oxygenation level in inactive muscle at exhaustion in incremental exercise in humans

The aim of the present study was to determine whether the oxygenation level in an inactive muscle during an incremental exercise test, determined by near-infrared spectroscopy, influences the maximal oxygen uptake (Vo2max). The oxygenation level at the onset of incremental exercise was higher than that at rest and started to decrease at a high power output. A minimal level was observed at exhaustion during incremental exercise. Vo2 increased linearly after some delay, and the rate of increase in Vo2 was greater at a higher power output. Heart rate increased linearly after the time delay, and the rate of increase in heart rate did not change. There was a significant correlation between Vo2max and oxygenation level in inactive muscle at exhaustion (r=-0.89). We therefore concluded that the oxygenation level in inactive muscle at exhaustion during incremental exercise is associated with an individual difference in Vo2max.

Effects of Angiotensin II on the Action Potential Durations of Atrial Myocytes in Hypertensive Rats

Angiotensin II (Ang II) has been reported to indirectly influence atrial electrical activity and to play a critical role in atrial arrhythmias in hypertensive patients. However, it is unclear whether Ang II has direct effects on the electrophysiological activity of the atrium affected by hypertension. We examined the effects of Ang II on the action potentials of atrial myocytes enzymatically isolated from spontaneous hypertensive rats (SHRs). The action potentials were recorded by the perforated patch-clamp technique and the atrial expression of the receptors AT1a and AT2 was measured by radioimmunoassay. Ang II significantly shortened the action potential durations (APDs) of SHRs without changes in the resting membrane potentials (RMPs). Pretreatment with selective AT1a blockers abolished the Ang II-induced reduction of atrial APDs of SHRs; however, a selective AT2 blocker did not, which was consistent with the results of the receptor assay. Pretreatment with phosphatidylinositol 3 (PI3)-kinase inhibitor, phospholipase C inhibitor, or protein kinase C (PKC) inhibitor abolished the Ang II-induced shortening of atrial APDs, but pertussis toxin and protein kinase A (PKA) inhibitor did not. To study the effects of chronic AT1a inhibition on Ang II-induced shortening of atrial APD, SHRs were treated with AT1a blocker for 4 weeks. AT1a blocker abolished the Ang II-induced reduction of atrial APDs of SHRs and also significantly lowered their blood pressure. In conclusion, Ang II shortened atrial APDs of SHRs via AT1a coupled with the Gq-mediated inositol triphosphate (IP3)-PKC pathway. Our findings indicated that Ang II caused atrial arrhythmias in hypertensive patients by shortening the effective refractory period of the atrium.

Chemosensitivity testing of ovarian cancer using the histoculture drug response assay: sensitivity to cisplatin and clinical response

Despite cytoreductive surgery and chemotherapy, the prognosis of advanced ovarian cancer is still poor. Predicting the chemosensitivity of tumors might improve the outcome. Therefore, we investigated the clinical value of the histoculture drug response assay for ovarian cancer. Tumor specimens were cultured for 7 days on collagen gel sponge in medium containing cisplatin, and the 50% inhibitory concentration was determined by the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyltetrazolium bromide assay. Then the in vitro sensitivity to cisplatin was compared with the clinical response and survival. Apoptosis of tumor cells was also investigated. Among 173 ovarian cancer patients, 164 were evaluable by the assay, and 29 patients had measurable lesions for which the clinical response could be determined. The 5-year survival rate was significantly higher in patients with chemosensitive tumors than in those with chemoresistant tumors when the cutoff value was set at a 50% inhibitory concentration of 25 μg/mL and the accuracy of the assay was 82.8% (24/29). As chemosensitivity to cisplatin became greater, the number of apoptotic cells also increased. This chemosensitivity assay may help predict the clinical response to cisplatin-based chemotherapy, thus improving the survival of ovarian cancer patients.

Relationship between maximal oxygen uptake and oxygenation level in inactive muscle at exhaustion in incremental exercise in humans

The aim of the present study was to determine whether the oxygenation level in an inactive muscle during an incremental exercise test, determined by near-infrared spectroscopy, influences the maximal oxygen uptake (Vo2max). The oxygenation level at the onset of incremental exercise was higher than that at rest and started to decrease at a high power output. A minimal level was observed at exhaustion during incremental exercise. Vo2 increased linearly after some delay, and the rate of increase in Vo2 was greater at a higher power output. Heart rate increased linearly after the time delay, and the rate of increase in heart rate did not change. There was a significant correlation between Vo2max and oxygenation level in inactive muscle at exhaustion (r = -0.89). We therefore concluded that the oxygenation level in inactive muscle at exhaustion during incremental exercise is associated with an individual difference in Vo2max.

Neuroprotective effects of the free radical scavenger Edaravone (MCI-186) in mice permanent focal brain ischemia

The present study was aimed to evaluate the effect of the free radical scavenger Edaravone on infarct volume due to permanent MCA occlusion in mice and, if so, to elucidate the mechanism of its neuroprotective effects. Male Balb/c mice were subjected to permanent middle cerebral artery occlusion and were treated with 3.0 mg/kg of Edaravone or vehicle 30 min before ischemia. Infarct volume was assessed by 2,3,5-triphenyltetrazolium chloride (TTC) method after 24 h. Furthermore, in situ detection of superoxide in the ipsilateral neocortex was carried out using the superoxide-sensitive dye dihydroethidium (DHE) staining technique. Pretreatment with 3.0 mg/kg of Edaravone ameliorated the tissue damage in the infarct rim and significantly reduced infarct volume to about 77% of the control (p<0.05). Semi-quantitative measurement of red fluorescence emitted from DHE revealed that the superoxide increased in the ischemic core at 1 h after the onset of ischemia and extended towards the infarct rim at 3 and 6 h, and that pretreatment with 3.0 mg/kg of Edaravone significantly inhibited the increase of superoxide in the infarct rim at 3 and 6 h (p<0.01). Double staining with DHE and monoclonal antibody against NeuN showed that the majority of the nuclei positive for DHE were also positive for NeuN. These findings suggest that Edaravone salvages the boundary zone of infarct by scavenging reactive oxygen species especially in the neurons during permanent focal cerebral ischemia.

Fluvastatin Enhances the Inhibitory Effects of a Selective AT 1 Receptor Blocker, Valsartan, on Atherosclerosis

We investigated the effects of a 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitor (statin) on the inhibitory effects of an angiotensin II type-1 receptor (AT1) blocker on atherosclerosis and explored cellular mechanisms. We gave apolipoprotein E null mice a high-cholesterol diet for 10 weeks and measured atherosclerotic plaque area and lipid deposition. Neither 1 mg/kg per day of valsartan nor 3 mg/kg per day of fluvastatin had any effect on blood pressure or cholesterol concentration; however, both drugs decreased plaque area and lipid deposition after 10 weeks. We then reduced the doses of both drugs to 0.1 mg/kg per day and 1 mg/kg per day, respectively. At these doses, neither drug had an effect on atherosclerotic lesions. When both drugs were combined at these doses, a significant reduction in atherosclerotic lesions was observed. Similar inhibitory effects of valsartan or fluvastatin on the expressions of nicotinamide-adenine dinucleotide/nicotinamide-adenine dinucleotide phosphate oxidase subunits p22phox and p47phox, production of superoxide anion, the expression of monocyte chemoattractant protein-1, and intercellular adhesion molecule-1 expression were observed. These results suggest that concomitant AT1 receptor and cholesterol biosynthesis blockade, particularly when given concomitantly, blunts oxidative stress and inflammation independent of blood pressure or cholesterol-related effects.

Nuclear receptor LXRalpha is involved in cAMP-mediated human renin gene expression

The cAMP-signaling pathway plays a crucial role in the regulation of the renin gene, but the mechanism involved remains poorly understood. We have focused our studies of renin gene regulation on the unique cAMP responsive element (huREN/CNRE, -135 to -107) in the human renin promoter. We have cloned a protein that binds to this unique CNRE and demonstrated that this protein is liver X receptor-alpha (LXRalpha), a transcriptional factor of the nuclear receptor family. Transient expression of LXRalpha in human renin-producing Calu-6 cells increased cAMP inducibility of human renin promoter. Similarly, LXRalpha-stably transfected Calu-6 cells exhibited increased cAMP inducibility of renin promoter as well as the endogenous renin gene. Site-directed mutation of huREN/CNRE, which disrupted LXRalpha binding, decreased cAMP-induced transcriptional activity of human renin promoter. Furthermore, we demonstrated that the binding of LXRalpha derived from human juxtaglomerular cells, the main production site of renin in the kidney, to the huREN/CNRE in vivo. These results suggest that LXRalpha plays an important role in the cAMP-mediated regulation of human renin gene transcription by binding to CNRE.

Possible Inhibition of Focal Cerebral Ischemia by Angiotensin II Type 2 Receptor Stimulation

Background— The role of angiotensin II receptor subtypes was investigated in focal brain ischemia induced by middle cerebral artery (MCA) occlusion.

Methods and Results— In Agtr2 + (wild-type) mice, MCA occlusion induced focal ischemia of ≈20% to 30% of the total area in coronal section of the brain. The ischemic area was significantly larger in angiotensin II type 2 receptor–deficient ( Agtr2 − ) mice than in Agtr2 + mice. The neurological deficit after MCA occlusion was also greater in Agtr2 − mice than in Agtr2 + mice. The decrease in surface cerebral blood flow after MCA occlusion was significantly exaggerated in the peripheral region of the MCA territory in Agtr2 − mice. Superoxide production and NADPH oxidase activity were enhanced in the ischemic area of the brain in Agtr2 − mice. An AT 1 receptor blocker, valsartan, at a nonhypotensive dose significantly inhibited the ischemic area, neurological deficit, and reduction of cerebral blood flow as well as superoxide production and NADPH oxidase activity in Agtr2 + mice. These inhibitory actions of valsartan were weaker in Agtr2 − mice.

Conclusions— These results suggest that AT 2 receptor stimulation has a protective effect on ischemic brain lesions, at least partly through the modulation of cerebral blood flow and superoxide production.

Roles of angiotensin type 1 and 2 receptors in pregnancy-associated blood pressure change

BACKGROUND

Activation of the renin-angiotensin system with increased levels of renin and angiotensin (Ang) II in pregnancy has been reported, but the vascular responsiveness to Ang II seems to be decreased, thereby keeping maternal blood pressure (BP) constant. We postulated that the balance of angiotensin type 1 (AT1) and angiotensin type 2 (AT2) receptor expression, which would exert antagonistic actions on vasoconstriction and cell growth, might control BP in pregnancy.

METHODS

Using wild type (C57BL/6J), AT1a receptor null and AT2 receptor null mice, we examined the changes in BP, expression and localization of AT1 and AT2 receptors in placenta, umbilical cord, and uterus by immunohistochemical staining and urinary albumin measurement during pregnancy.

RESULTS

Wild type mice did not show any significant change in BP throughout pregnancy. The BP in AT1a receptor null mice declined significantly in the second trimester of pregnancy, whereas BP in AT2 receptor null mice increased significantly in the third trimester. We did not observe any significant differences in albuminuria, litter size, or body weight of neonates among the three groups. Vascular smooth muscle cells in blood vessels of the umbilical cord and placenta specifically expressed AT2 receptors, which are minimally expressed in adult vessels. In contrast, AT1 receptors were dominantly expressed in the cytotrophoblast and chorionic plate as well as blood vessels in placenta and umbilical cord.

CONCLUSIONS

Our results suggested that disturbance of the balance of the AT1 and AT2 receptors could trigger pregnancy induced hypertension.

Trans-inactivation of receptor tyrosine kinases by novel angiotensin II AT2 receptor-interacting protein, ATIP

Negative regulation of mitogenic pathways is a fundamental process that remains poorly characterized. The angiotensin II AT2 receptor is a rare example of a 7-transmembrane domain receptor that negatively cross-talks with receptor tyrosine kinases to inhibit cell growth. In the present study, we report the molecular cloning of a novel protein, ATIP1 (AT2-interacting protein), which interacts with the C-terminal tail of the AT2 receptor, but not with those of other receptors such as angiotensin AT1, bradykinin BK2, and adrenergic beta(2) receptor. ATIP1 defines a family of at least four members that possess the same domain of interaction with the AT2 receptor, contain a large coiled-coil region, and are able to dimerize. Ectopic expression of ATIP1 in eukaryotic cells leads to inhibition of insulin, basic fibroblast growth factor, and epidermal growth factor-induced ERK2 activation and DNA synthesis, and attenuates insulin receptor autophosphorylation, in the same way as the AT2 receptor. The inhibitory effect of ATIP1 requires expression, but not ligand activation, of the AT2 receptor and is further increased in the presence of Ang II, indicating that ATIP1 cooperates with AT2 to transinactivate receptor tyrosine kinases. Our findings therefore identify ATIP1 as a novel early component of growth inhibitory signaling cascade.

Angiotensin II type-1 receptor blocker valsartan enhances insulin sensitivity in skeletal muscles of diabetic mice

Angiotensin II has been shown to contribute to the pathogenesis of insulin resistance; however, the mechanism is not well understood. The present study was undertaken to investigate the potential effect of an angiotensin II type-1 (AT1) receptor blocker, valsartan, to improve insulin resistance and to explore the signaling basis of cross-talk of the AT1 receptor- and insulin-mediated signaling in type 2 diabetic KK-Ay mice. Treatment of KK-Ay mice with valsartan at a dose of 1 mg/kg per day, which did not influence systolic blood pressure, significantly increased insulin-mediated 2-[3H]deoxy-d-glucose (2-[3H]DG) uptake into skeletal muscle and attenuated the increase in plasma glucose concentration after a glucose load and plasma concentrations of glucose and insulin. In contrast, insulin-mediated 2-[3H]DG uptake into skeletal muscle was not influenced in AT2 receptor null mice, and an AT2 receptor blocker, PD123319, did not affect 2-[3H]DG uptake and superoxide production in skeletal muscle of KK-Ay mice. Moreover, we observed that valsartan treatment exaggerated the insulin-induced phosphorylation of IRS-1, the association of IRS-1 with the p85 regulatory subunit of phosphoinositide 3 kinase (PI 3-K), PI 3-K activity, and translocation of GLUT4 to the plasma membrane. It also reduced tumor necrosis factor-alpha (TNF-alpha) expression and superoxide production in skeletal muscle of KK-Ay mice. Specific AT1 receptor blockade increases insulin sensitivity and glucose uptake in skeletal muscle of KK-Ay mice via stimulating the insulin signaling cascade and consequent enhancement of GLUT4 translocation to the plasma membrane.

Experimental transmission of abnormal prion protein (PrPsc) in the small intestinal epithelial cells of neonatal mice

Using an immunohistochemical method, we attempted to detect the transmission of abnormal prion protein (PrPsc) to the enterocytes of the small intestine of neonatal mice by oral exposure with sheep brain affected by scrapie. Five 1-day-old neonatal mice were exposed by oral inoculation to the homogenized brain of a scrapie-affected sheep. In the small intestine of all mice 1 hour after inoculation, immunoreactivity with antinormal prion protein (PrPc) antibody was seen in the cytoplasm of villus enterocytes. This finding suggests transmission of abnormal PrPsc into the cytoplasm of enterocytes. In control mice treated with normal sheep brain, no PrPc signal was seen in enterocytes of the small intestine. Immunopositivity for neurofilament protein and glial fibrillary acidic protein was seen in the cytoplasm of enterocytes of mice inoculated with scrapie and normal sheep brain. This suggests that the enterocytes of neonatal mice can absorb PrPsc and other macromolecular proteins of the sheep brain affected by scrapie and may be more important than previously thought as a pathway for PrPsc transmission in neonatal animals.

Regulation of Inhibitory Protein-κB and Monocyte Chemoattractant Protein-1 by Angiotensin II Type 2 Receptor-Activated Src Homology Protein Tyrosine Phosphatase-1 in Fetal Vascular Smooth Muscle Cells

In the present study we examined the effects of angiotensin II (Ang II) type 2 (AT(2)) receptor stimulation on AT(1) receptor-mediated monocyte chemoattractant protein-1 (MCP-1) expression and the possible mechanisms of AT(2) receptor-mediated signaling in cultured rat fetal vascular smooth muscle cells, which express both AT(1) and AT(2) receptors. Ang II stimulation induced MCP-1 mRNA expression as well as an increase in nuclear factor-kappaB (NF-kappaB) binding to the corresponding cis DNA element of the MCP-1 promoter region and a decrease in the cytosolic inhibitory protein-kappaB (IkappaB) protein level via AT(1) receptor stimulation, whereas stimulation of the AT(2) receptor decreased Ang II-induced MCP-1 expression, NF-kappaB DNA binding, and IkappaB degradation, suggesting that activation of the AT(2) receptor attenuated AT(1) receptor-mediated MCP-1 expression via a decrease in NF-kappaB DNA binding and an increase in IkappaB stability. Moreover, we demonstrated that AT(2) receptor stimulation attenuated TNFalpha-mediated NF-kappaB activation and MCP-1 expression. A tyrosine phosphatase inhibitor, orthovanadate, attenuated the AT(2) receptor-mediated increase in IkappaB protein. Moreover, we observed that two IkappaB subunits (IkappaBalpha and IkappaBbeta) were tyrosine-phosphorylated after Ang II stimulation. Transfection of a dominant-negative Src homology protein tyrosine phosphatase-1 mutant into vascular smooth muscle cells inhibited the AT(2) receptor-mediated increase in IkappaB, leading to a significant increase in AT(1) receptor-induced NF-kappaB activation and MCP-1 expression. Taken together, our results demonstrated that AT(2) receptor stimulation attenuated MCP-1 expression via IkappaB stabilization, and Src homology protein tyrosine phosphatase-1 might play a critical role in the transcriptional regulation of MCP-1 expression through the control of IkappaB protein stability.

Calcium channel blocker azelnidipine enhances vascular protective effects of AT1 receptor blocker olmesartan

The present studies were undertaken to investigate the potential effect of a calcium channel blocker (CCB) to enhance the inhibitory effect of an angiotensin (Ang) II type 1 (AT1) receptor blocker (ARB) on vascular injury and the cellular mechanism of the effect of CCB on vascular remodeling. In polyethylene cuff-induced vascular injury of the mouse femoral artery, proliferation of vascular smooth muscle cells (VSMCs) and neointimal formation associated with activation of extracellular signal-regulated kinase (ERK), and tyrosine-phosphorylation of signal transducer and activator of transcription (STAT)1 and STAT3, inflammatory response assessed by monocyte chemoattractant protein-1 and tumor necrosis factor-alpha expression, as well as oxidative stress such as expression of NADH/NADPH oxidase p22(phox) subunit and superoxide production, were less in AT1a receptor null mice. Administration of nonhypotensive doses of a CCB, azelnidipine (0.5 or 1 mg/kg per day) attenuated these parameters in wild-type and AT1a receptor null mice. Coadministration of lower doses of an ARB, olmesartan (0.5 mg/kg per day), and azelnidipine (0.1 mg/kg per day), which did not affect vascular remodeling, significantly inhibited these parameters in wild-type mice. Moreover, the effective dose of azelnidipine (1 mg/kg per day) exaggerated the inhibitory action of olmesartan at effective doses of 1 or 3 mg/kg per day on VSMC proliferation in the injured arteries. These results suggest that azelnidipine could inhibit vascular injury at least partly independent of the inhibition of AT1 receptor activation and that azelnidipine could exaggerate the vascular protective effects of olmesartan, suggesting clinical possibility that the combination of CCB and ARB could be more effective in the treatment of vascular diseases.

Nicotine Enhances Angiotensin II-Induced Mitogenic Response in Vascular Smooth Muscle Cells and Fibroblasts

Objective— The pathogenetic mechanism of tobacco-related cardiovascular diseases is still not well defined. We examined the potential possibility of an interaction between nicotine, a major component of cigarette smoke, and angiotensin II (Ang II), which plays an important role in the pathogenesis of cardiovascular diseases characterized by Ang II type 1 (AT 1 ) receptor-mediated abnormal growth of vascular smooth muscle cells (VSMC) and fibroblasts.

Methods and Results— Nicotine or Ang II-stimulated [ 3 H]thymidine incorporation and c-fos expression in adult rat aortic VSMC and adventitial fibroblast. The nicotine-induced DNA synthesis was not affected by valsartan, an AT 1 receptor-specific blocker, or PD123319, an Ang II type 2 (AT 2 ) receptor-specific antagonist. Nicotine or Ang II stimulation rapidly increased extracellular signal-regulated kinase (ERK) activation, tyrosine- and serine-phosphorylation of signal transducer and activator of transcription (STAT)1 and STAT3, and p38 mitogen-activated protein kinase (p38 MAPK), in both cell types. Interestingly, co-administration of nicotine and Ang II at lower doses, which did not affect cell growth, induced DNA synthesis and c-fos expression accompanied by enhancement of ERK, STAT, and p38MAPK activity. PD98059, a mitogen-activated protein kinase/ERK kinase inhibitor, or SB23058, a p38MAPK inhibitor, significantly attenuated the vasotrophic effect of nicotine and Ang II.

Conclusions— These results suggest that nicotine exerts a growth-promoting effect on vascular cells and enhances the Ang II-induced vasotrophic effect, which is at least partly mediated by the activation of ERK, STAT, and p38MAPK.

[Angiotensin II receptor]

The peptide angiotensin(Ang) II exerts hemodynamic, and renal as well as cardiovascular structural effects. Multiple lines of evidence have suggested the existence of several Ang II receptor subtypes. Recent evidence has revealed that the functions of the AT1 and AT2 receptors are mutually antagonistic in various cells and tissues. The effect of AT1 blocker(ARB) may not be entirely due to the blockade of the AT1 receptor. When AT1 receptor is blocked and unbound Ang II may act on AT2 receptor and Ang 1-7 and Ang IV via AT4 receptor might be involved in the effects of ARB. If the AT2 receptor contributes to the pathogenesis and consequent remodeling of cardiovascular diseases in human, ARB may have some specific effects in the treatment of cardiovascular diseases. A more extensive knowledge of the AT2 receptor could therefore contribute to the understanding of the clinical beneficial effects of ARB.

Regulation of collagen synthesis in mouse skin fibroblasts by distinct angiotensin II receptor subtypes

We examined the possibility of whether angiotensin (Ang) II type 1 (AT1) and type 2 (AT2) receptor stimulation differentially regulates collagen production in mouse skin fibroblasts. Both AT1 and AT2 receptors were expressed in neonatal skin fibroblasts prepared from wild-type mice to a similar degree, and the AT1a receptor was exclusively expressed as opposed to the AT1b receptor. In wild-type fibroblasts, Ang II increased collagen synthesis accompanied by an increase in expression of tissue inhibitor of metalloproteinase (TIMP)-1, and these increases were inhibited by valsartan, an AT1 receptor blocker, but augmented by PD123319, an AT2 receptor antagonist. Ang II decreased basal and IGF-I-induced collagen production and inhibited TIMP-1 expression in neonatal skin fibroblasts prepared from AT1a knockout (KO) mice. These Ang II-mediated inhibitory effects on collagen production and TIMP-1 expression observed in AT1a KO fibroblasts were attenuated by the addition of PD123319 or a tyrosine phosphatase inhibitor, sodium orthovanadate, but not affected by a serine/threonine phosphatase inhibitor, okadaic acid. Moreover, we demonstrated that transfection of a catalytically inactive, dominant negative SHP-1 (Src homology 2-containing protein-tyrosine phosphatase-1) mutant inhibited the Ang II-mediated inhibitory effect on both collagen synthesis and TIMP-1 expression in AT1a KO fibroblasts. These results suggest that AT1a receptor stimulation increases collagen production in skin fibroblasts at least in part due to the inhibition of collagen degradation via the increase in TIMP-1 expression, whereas AT2 receptor stimulation exerts inhibitory effects on TIMP-1 expression, which is mediated at least partially by the activation of SHP-1, thereby possibly inhibiting collagen production.

Expression of endothelial angiotensin II receptor mRNA in pregnancy-induced hypertension

OBJECTIVE

The normal suppression of vascular sensitivity to angiotensin II (Ang II) in pregnancy is lost in pregnancy-induced hypertension (PIH). To examine the mechanism, we investigated Ang II receptor subtype 1 (AT1R) and 2 (AT2R) expression in human umbilical vein endothelial cells (HUVEC) and vascular smooth muscle cells (VSMC).

METHODS

The HUVEC and VSMC were incubated with serum from normal pregnant women and PIH patients for 0 to 12 h. The AT1R and AT2R mRNA were semiquantified as the ratio to glyceraldehyde-3-phosphate dehydrogenase mRNA, using multiplex reverse transcription-polymerase chain reaction. The AT1R expression was also evaluated by immunocytochemistry.

RESULTS

Serum from PIH patients significantly increased AT1R mRNA of HUVEC (1.48 +/- 0.44) after a 12-h incubation compared with that from normal pregnant women (0.25 +/- 0.14). On the other hand, AT2R mRNA of HUVEC incubated with serum from PIH patients (0.14 +/- 0.02) was significantly decreased compared with HUVEC incubated with serum from normal pregnant women (0.31 +/- 0.08). The AT1R mRNA of VSMC was significantly increased by serum from both PIH patients and normal pregnant women. The AT1R-to-AT2R mRNA ratio increased by serum from PIH patients was significantly reduced by anti-tumor necrosis factor-alpha (TNF-alpha) antibody (20 microg/mL). Valsartan (an AT1R antagonist, at 1 to 10 nmol/L) significantly increased AT2R mRNA of HUVEC. Also, immunocytochemistry demonstrated that endothelial AT1R expression was strongly increased by PIH sera and reduced by anti-TNF-alpha antibody.

CONCLUSIONS

Endothelial AT1R expression is increased and AT2R expression is decreased in PIH. The TNF-alpha is related to the pathogenesis of PIH by reduced AT2R mRNA through an increase of AT1R mRNA.

Important role of nitric oxide in the effect of angiotensin-converting enzyme inhibitor imidapril on vascular injury

To examine the possible role of the bradykinin-NO system in the action of ACE inhibitors, we studied the effects of imidapril, an ACE inhibitor, on inflammatory vascular injury by using AT1a-receptor-deficient (AT1aKO) mice. A polyethylene cuff was placed around the femoral artery of AT1aKO mice and wild-type (WT; C57BL/6J) mice. Neointimal area in cross sections of the artery was measured 14 days after cuff placement. A low dose of imidapril (1 mg/kg per day), which did not affect blood pressure, was administered by gavage. Expression of monocyte chemoattractant protein (MCP)-1 and tumor necrosis factor (TNF)-alpha was detected by immunohistochemical staining and reverse transcriptase-polymerase chain reaction (RT-PCR) 7 days after the operation. Neointimal formation, vascular smooth muscle cell proliferation, and expression of MCP-1 and TNF-alpha were attenuated in the injured artery in AT1aKO mice compared with those in WT mice. Imidapril inhibited neointimal formation, DNA synthesis of vascular smooth muscle cells, and expression of MCP-1 and TNF-alpha in AT1aKO mice as well as in WT mice. In addition, imidapril increased tissue cGMP content after cuff placement. These inhibitory effects of imidapril were significantly reduced or abolished by a bradykinin receptor antagonist, Hoechst 140, or an NO synthase inhibitor, L-NAME, both in WT and AT1aKO mice. Treatment with imidapril did not change AT2 receptor and ACE expression detected by RT-PCR in the injured artery. These results indicate that not only blockade of angiotensin II production but also activation of the bradykinin-NO system plays an important role in the beneficial effects of imidapril on vascular remodeling.

Angiotensin II type 2 receptor deficiency exacerbates heart failure and reduces survival after acute myocardial infarction in mice

BACKGROUND

Angiotensin II plays a prominent role in the progression of heart failure after acute myocardial infarction (AMI). Although both angiotensin type 1 (AT1) and type 2 (AT2) receptors are known to be present in the heart, comparatively little is known about the latter. We therefore examined the role played by AT2 receptors in post-AMI heart failure.

METHODS AND RESULTS

In wild-type mice subjected to AMI by coronary artery ligation, AT2 receptor immunoreactivity is upregulated in the infarct and border areas. Among AT2 receptor-null (-/-) mice, the 7-day survival rate after AMI was significantly lower than among wild-type mice (43% versus 67%; P<0.05). All sham-operated animals of both genotypes survived through the study. Ventricular mRNA levels for brain natriuretic peptide were elevated in both genotypes 24 hours after coronary occlusion, with levels in AT2-/- significantly higher than in wild-type mice, as were their lung weights, and histological examination revealed marked pulmonary congestion in the AT2-/- mice. Cardiac function was significantly decreased in AT2-/- mice 2 days after AMI.

CONCLUSIONS

AT2 receptor deficiency exacerbates short-term death rates and heart failure after experimental AMI in mice. The AT2 receptor may thus exert a protective effect on the heart after AMI.

[Renin-angiotensin system and heart failure]

The local renin-angiotensin system in cardiac tissue has been demonstrated to be involved in the pathophysiology of cardiac hypertrophy and heart failure. Angiotensin II type 1(AT1) receptor stimulation leads to vasoconstriction, cell growth, oxidation, aldosterone release, and fibrosis. Recent evidence suggests that angiotensin II type 2(AT2) receptor exerts cardioprotective effects by counteracting against AT1 receptor. However, the role of AT2 receptor signaling in cardiac hypertrophy and fibrosis still remain controversial. This review focused on the accumulating evidence for the cardiac renin-angiotensin system in heart failure.

Effects of Ghrelin on growth hormone secretion from cultured adenohypophysial cells in pigs

To clarify the direct effects of Ghrelin on growth hormone (GH) release from anterior pituitary (AP) cells in pigs, GH-releasing effects of human Ghrelin (hGhrelin) and rat Ghrelin (rGhrelin) on porcine AP cells were compared with GHRH in vitro. The AP cells were obtained from 6-month-old pigs and the cells (2 x 10(5) cells per well) were incubated for 2 h with the peptides after incubating in DMEM for 3 days. hGhrelin and rGhrelin significantly stimulated GH release from the cultured cells at doses of 10(-8) and 10(-7)M (P < 0.05). The rates of increase in GH at 10(-8) and 10(-7)M of hGhrelin were 82.7 and 131.9%, while those with rGhrelin were 43.9 and 79.5%, respectively. GHRH significantly stimulated GH release from the cells at a dose as low as 10(-11)M (P < 0.05), and the response to GHRH was greater than that induced by Ghrelins. In time-course experiments, GHRH continued to increase GH concentrations in media until 120 min after incubation; however, those in media treated with hGhrelin reached a plateau 60 min after incubation, and the maximal value was approximately one third that obtained with GHRH. When hGhrelin (10(-8)M) and GHRH (10(-8)M) were added together, additive effects of both peptides on the release of GH were observed (P < 0.05). Somatostatin (SS, 10(-7)M) significantly blunted GH release induced by hGhrelin (10(-8)M) and GHRH (10(-8)M) (P < 0.05). In the presence of SS, additive effects of hGhrelin and GHRH on the release of GH were observed (P < 0.05). These results show that Ghrelin directly stimulates GH release from anterior pituitary cells in pigs; however, the GH-releasing effect is weaker than that of GHRH in vitro. The present results also show that Ghrelin interacts with GHRH and SS to in the release of GH from porcine adenohypophysial cells.

Cardioprotective role of AT2 receptor in postinfarction left ventricular remodeling

The aim of this study was to determine the role of the AT2 receptor (AT2R) in left ventricular (LV) remodeling after myocardial infarction (MI). The left anterior descending arteries were ligated in AT2R gene knockout (Agtr2-) and wild-type (Agtr2+) mice. The LV remodeling was evaluated by echocardiography and histology over a period of 2 weeks after MI. The infarct sizes in hearts excised from Agtr2+ and Agtr2- mice on day 1 were similar. The mortality rate of Agtr2- mice (62.9%) on day 14 after MI was significantly (P<0.05) higher than that of Agtr2+ mice (39.7%). Accordingly, LV/body weight ratios (3.7+/-0.2 versus 3.0+/-0.1 on day 14) and LV end-diastolic (4.8+/-0.3 versus 3.9+/-0.4 mm on day 7) and end-systolic (4.4+/-0.3 versus 3.2+/-0.6 mm on day 7) dimensions evaluated by echocardiography were significantly greater in Agtr2- than in Agtr2+ mice. The rates of ventricular arrhythmia, rates of cardiac rupture, and blood pressures in the 2 strains were similar after MI. Myocyte cross-sectional areas were increased after MI, but the magnitudes were similar in Agtr2+ and Agtr2- mice, indicating the greater increases in LV dimensions and weight in Agtr2- mice are due to elongation of myocyte length and/or an increase in the interstitial weight (including vasculatures, infiltrated cells, and interstitial fluid). Interstitial fibrosis in remote myocardium was not evident in either strain. These results indicate AT2R plays a significant role in the protection against early development of LV dilation, thereby reducing the early mortality rate after MI.

Inhibition of experimental intimal thickening in mice lacking a novel G-protein-coupled receptor

BACKGROUND

Vascular restenosis attributable to intimal thickening remains a major problem after percutaneous transluminal coronary angioplasty (PTCA).

METHODS AND RESULTS

Through differential-display analysis, we have identified a novel gene whose expression was increased after catheter injury of rabbit aorta. The gene that is expressed predominantly in vascular smooth muscle cells encodes a novel protein with 7 transmembrane domains, and we termed it ITR (intimal thickness-related receptor). The ITR sequence contains a motif common to the Rhodopsin-like GPCR (G-protein-coupled receptor) superfamily. In vivo analyses of this gene revealed that expression of ITR protein increased with intimal thickening induced by cuff placement around murine femoral artery. Furthermore, ITR-knockout mice were found to be resistant to this experimental intimal thickening.

CONCLUSIONS

ITR thus seems to be a novel receptor that may play a role in vascular remodeling and that may represent a good target for development of drugs in the prevention of vascular restenosis.

Fluvastatin enhances the inhibitory effects of a selective angiotensin II type 1 receptor blocker, valsartan, on vascular neointimal formation

BACKGROUND

The present studies were undertaken to investigate the potential effect of a hydroxymethylglutaryl coenzyme A reductase inhibitor (statin) to enhance the inhibitory effect of an angiotensin (Ang) II type 1 (AT1) receptor blocker (ARB) on vascular neointimal formation and to explore the cellular mechanism of cross-talk of the AT1 receptor and statin in vascular smooth muscle cells (VSMCs).

METHODS AND RESULTS

Neointimal formation and the proliferation of VSMCs induced by cuff placement around the femoral artery were significantly inhibited by treatment with an ARB, valsartan, at a dose of 0.1 mg x kg(-1) x d(-1) and with fluvastatin at a dose of 1 mg x kg(-1) x d(-1), which did not influence mean arterial blood pressure or plasma cholesterol level, whereas valsartan or fluvastatin alone at these doses did not affect neointimal formation or the proliferation of VSMCs. Pretreatment with fluvastatin (approximately 5 micromol/L) for 24 hours significantly inhibited Ang II (1 micromol/L)-mediated DNA synthesis and c-fos promoter activity in cultured VSMCs. Moreover, pretreatment of VSMCs with fluvastatin significantly inhibited Ang II-mediated extracellular signal-regulated kinase (ERK) activation and tyrosine- and serine-phosphorylation of signal transducer and activator of transcription (STAT)1 and STAT3. AT1 receptor-mediated recruitment of Rac-1 to Janus kinase (Jak) family/STATs was also inhibited by fluvastatin. Consistent with these in vitro results, phosphorylation of ERK, STAT1, and STAT3 was attenuated by the coadministration of valsartan and fluvastatin even at low doses in vivo.

CONCLUSION

These results suggest that the cholesterol-independent inhibition of AT1 receptor-mediated VSMC proliferation by statins may contribute to the beneficial effects of statins combined with an ARB on vascular diseases.

Role of AT2 receptor in the brain in regulation of blood pressure and water intake

The effects of intracerebroventricular (ICV) injection of angiotensin II (ANG II) on blood pressure and water intake were examined with the use of ANG II receptor-deficient mice. ICV injection of ANG II increased systolic blood pressure in a dose-dependent manner in wild-type (WT) mice and ANG type 2 AT(2) receptor null (knockout) (AT(2)KO) mice; however, this increase was significantly greater in AT(2)KO mice than in WT mice. The pressor response to a central injection of ANG II in WT mice was inhibited by ICV preinjection of the selective AT(1) receptor blocker valsartan but exaggerated by the AT(2) receptor blocker PD-123319. ICV injection of ANG II also increased water intake. It was partly but significantly suppressed both in AT(2)KO and AT(1)aKO mice. Water intake in AT(2)/AT(1)aKO mice did not respond to ICV injection of ANG II. Both valsartan and PD-123319 partly inhibited water intake in WT mice. These results indicate an antagonistic action between central AT(1)a and AT(2) receptors in the regulation of blood pressure, but they act synergistically in the regulation of water intake induced by ANG II.

Effect of estrogen and AT1 receptor blocker on neointima formation

The present study explored the possibility that estrogen may enhance the inhibitory effect of an angiotensin (Ang) II type 1 (AT1) receptor blocker on neointima formation in vascular injury, and investigated the signaling mechanism involved in their actions. Polyethylene cuff placement around the femoral artery of mice induced neointima formation and increased bromodeoxyuridine (BrdU) incorporation into vascular smooth muscle cells. These changes were significantly smaller in female mice than in male mice. Ovariectomy enhanced neointima formation and BrdU incorporation in the injured artery, which were reversed by 17beta-estradiol (80 microg/kg per day) replacement. Treatment with a selective AT1 receptor blocker, olmesartan (3 mg/kg per day), significantly inhibited neointima formation and BrdU incorporation, whereas the inhibitory effects of olmesartan were more marked in intact female mice than in male or ovariectomized mice. Phosphorylation of extracellular signal-regulated kinase (ERK), signal transducer and activator of transcription (STAT) 1, and STAT3 was increased in the injured artery. These increases were significantly smaller in intact female mice than in male or ovariectomized mice. Olmesartan or estrogen attenuated the phosphorylation of ERK and STAT in the injured artery, whereas these inhibitory effects were greater in intact female mice. Lower doses of olmesartan (0.5 mg/kg per day) or 17beta-estradiol (20 microg/kg per day) did not influence neointima formation, BrdU incorporation, and ERK and STAT phosphorylation in ovariectomized mice, whereas coadministration of olmesartan and 17beta-estradiol at these doses attenuated these parameters. These results indicate that estrogen and an AT1 receptor blocker synergistically attenuate vascular remodeling, which is at least partly via inhibition of ERK and STAT activity.

[Recent progress in AT1 and AT2 receptor research]

AT1 and AT2 receptors seem to be mutually antagonistic and the upregulation of AT2 receptor would play a role in the pathogenesis and remodeling of cardiovascular and renal diseases. AT2 receptor is abundantly and widely expressed in fetal tissues, but present at low levels in adult tissues and re-expressed in certain pathological conditions such as vascular injury. The overall cellular effect of AT2 and AT1 receptors co-stimulation is a premature termination of AT1 receptors-elicited cell growth signals by AT2 receptors. Our recent results using AT2 receptor null mice suggest that selective AT1 receptor blockade as well as the stimulation of uninhibited AT2 receptor by angiotensin II is important in the ARB-mediated improvement of cardiovascular remodeling.

Angiotensin II subtype 2 receptor activation inhibits insulin-induced phosphoinositide 3-kinase and Akt and induces apoptosis in PC12W cells

In the present study, we identified novel negative cross-talk between the angiotensin II subtype 2 (AT2) receptor and insulin receptor signaling in the regulation of phosphoinositide 3-kinase (PI3K), Akt, and apoptosis in rat pheochromocytoma cell line, PC12W cells, which exclusively express AT2 receptor. We demonstrated that insulin-mediated insulin receptor substrate (IRS)-2-associated PI3K activity was inhibited by AT2 receptor stimulation, whereas IRS-1-associated PI3K activity was not significantly influenced. AT2 receptor stimulation did not change insulin-induced tyrosine phosphorylation of IRS-2 or its association with the p85alpha subunit of PI3K, but led to a significant reduction of insulin-induced p85alpha phosphorylation. AT2 receptor stimulation increased the association of a protein tyrosine phosphatase, SHP-1, with IRS-2. Moreover, we demonstrated that AT2 receptor stimulation inhibited insulin-induced Akt phosphorylation and that insulin-mediated antiapoptotic effect was also blocked by AT2 receptor activation. Overexpression of a catalytically inactive dominant negative SHP-1 markedly attenuated the AT2 receptor- mediated inhibition of IRS-2-associated PI3K activity, Akt phosphorylation, and antiapoptotic effect induced by insulin. Taken together, these results indicate that AT2 receptor-mediated activation of SHP-1 and the consequent inhibition IRS-2-associated PI3K activity contributed at least partly to the inhibition of Akt phosphorylation, thereby inducing apoptosis.