Biomedical subjects

S Umemura

Publications and source records attributed to S Umemura.

At least 19 recordsLinked to original sources

PubMed1998

Genetic deficiency of angiotensinogen produces an impaired urine concentrating ability in mice.

Angiotensinogen gene-knockout (Atg-/-) mice lacking angiotensin II exhibit chronic hypotension. The present study was designed to investigate pathophysiology of Atg-/- mice from the renal functional view. Wild-type (Atg+/+) and Atg-/- mice at 10 weeks of age were housed in metabolic cages for 24-hour urine collection. When provided free access to water, Atg-/- mice showed an increased urine output and a decreased urine osmolality compared with Atg+/+ mice. Urinary excretion and plasma levels of vasopressin were significantly higher in mutant mice than in wild-type mice. On the other hand, urinary excretion of aldosterone in mutant mice was suppressed to the levels under the detection limit of the assay system. The mean plasma aldosterone level of Atg-/- mice was suppressed to 30% of that of Atg+/+ mice. Plasma levels of creatinine, endogenous creatinine clearance, and urinary electrolyte excretion were not different between these mice. In Atg+/+ mice, urine osmolality was markedly increased from 1929 +/- 21 to 3314 +/- 402 mOsm/kg during water deprivation, whereas this parameter in Atg-/- mice did not change significantly (from 1413 +/- 121 to 1590 +/- 92 mOsm/kg). Urinary vasopressin excretion increased during water deprivation from 0.24 +/- 0.04 and 0.70 +/- 0.08 to 0.42 +/- 0.06 and 2.31 +/- 0.35 ng/mg creatinine in wild-type and mutant mice, respectively. Histologic study revealed interstitial inflammation, and atrophic changes in the tubules and papilla in Atg-/- mice. In conclusion, a genetic deficiency of angiotensinogen produced an impaired urine concentrating ability and tubulointerstitial lesions, indicating the critical role of angiotensinogen in developing normal tubular function and construction.

Aldosterone↗

PubMed1998

Increased cardiac angiotensin II receptors in angiotensinogen-deficient mice.

Two subtypes of angiotensin II (Ang II) receptors, type 1 (AT1-R) and type 2 (AT2-R), have been identified in the heart. However, little is known about the regulation of cardiac AT1-R and AT2-R by Ang II in vivo. Thus, we examined cardiac AT1-R and AT2-R in angiotensinogen-deficient (Atg-/-) mice that are hypotensive and lack circulating Ang II. Cardiac Ang II receptors (Ang II-R) were assessed by radioligand binding with 125I-[Sar1,Ile8]-Ang II in plasma membrane fractions. AT1-R and AT2-R were distinguished using their specific antagonists CV-11974 and PD123319, respectively. Total densities of Ang II-R and AT1-R density were significantly greater in the Atg-/- mice than Atg+/+ mice (31.1+/-2.8 versus 18.8+/-2.1, 28.7+/-3.0 versus 16.9+/-2.3 fmol/mg protein, P<.01, respectively), and AT2-R showed a slight but not significant increase in Atg-/- mice relative to Atg+/+ control animals. Kd values were not different between the two groups. In contrast to binding experiments, levels of Ang II type 1a receptor (AT1a-R) and AT2-R mRNA did not differ between Atg-/- and Atg+/+ mice. These results suggest that lack of Ang II may upregulate AT1-R through translational and/or posttranslational mechanisms in Atg-/- mice.

Angiotensin II↗

PubMed1998

Dietary salt loading decreases the expressions of neuronal-type nitric oxide synthase and renin in the juxtaglomerular apparatus of angiotensinogen gene-knockout mice.

The present study investigates whether neuronal type nitric oxide synthase (N-NOS) in the macula densa participates in the regulation of renal renin expression during altered dietary salt intake in angiotensinogen gene-knockout (Atg-/-) mice. Wild-type (Atg+/+) and Atg+/+ mice were fed a low-salt (0.04% NaCl), normal-salt (0.3% NaCl), or high-salt (4% NaCl) diet for 2 wk. Histochemical staining for NADPH diaphorase (NADPHd) and renin were analyzed morphometrically. Levels of N-NOS and renin mRNA in renal cortical tissues were determined by reverse transcription-PCR and Northern blot analysis, respectively. In animals fed a normal-salt diet, the renal expressions of N-NOS and renin were markedly increased in Atg-/- mice compared with Atg+/+ mice. When mutant mice were fed a high-salt diet, the signal intensity of the NADPHd reaction and the number of positively stained macula densa cells were significantly decreased. The levels of renal cortical N-NOS mRNA were also suppressed by the treatment. These changes were paralleled by decreases in renal renin-immunoreactive areas and the levels of renin mRNA. On the other hand, salt restriction did not produce further significant increases in the renal N-NOS and renin expressions in mutant mice, whereas a parallel inverse relationship was observed between these enzyme expressions and the levels of salt intake in wild-type mice. These results suggest that the N-NOS expression in the macula densa is inversely regulated by salt intake and that the enzyme activity is functionally linked to renal renin production. Salt-modulated renal N-NOS and renin expressions are independent on angiotensin formation in Atg-/- mice.

Animals↗

PubMed1997

A novel proximal element mediates the regulation of mouse Ren-1C promoter by retinoblastoma protein in cultured cells.

The protein product of the retinoblastoma susceptibility gene, RB, is a nuclear phosphoprotein that modulates transcription of genes involved in growth control via interactions with transcription factors. Renin is a rate-limiting enzyme of the renin-angiotensin system that regulates blood pressure and water-electrolyte balance. Renin gene expression is regulated in a tissue-specific and developmentally linked manner. Similarly, the expression of RB is controlled in a differentiation-linked manner. Thus, to investigate whether RB is involved in the regulation of renin gene expression, we examined the effects of RB on transcriptional activity of the mouse renin (Ren-1C) promoter. The Ren-1C promoter contains two transcriptionally important elements; the RU-1 (-224 to -138) and RP-2 (-75 to -47) elements. RB activated the Ren-1C promoter in human embryonic kidney cells. The promoter element responsible for RB-mediated transcriptional regulation was the RP-2 element. The results of DNA-protein binding experiments showed that RB increased nuclear binding activity to the RP-2 element, and site-directed mutation which disrupted binding of nuclear factors to the RP-2 element markedly reduced RB-mediated activation of Ren-1C promoter in human embryonic kidney cells. These results indicate that the RP-2 element plays an important role in RB-mediated transcriptional regulation of Ren-1C promoter activity in human embryonic kidney cells, thereby suggesting an interesting mechanism by which RB may modulate the renin-angiotensin system.

Activating Transcription Factors↗

PubMed1997

Stretch-induced MAP kinase activation in cardiomyocytes of angiotensinogen-deficient mice.

The renin-angiotensin system plays an important role in the hypertrophic responses in cardiac myocytes through the activation of signal transduction pathways and expression of oncogenes. In the present study, we examined mechanical stretch-induced activation of mitogen-activated protein kinases (MAP kinases) using cultured cardiac myocytes derived from neonatal angiotensinogen gene deficient mice (Agt-/-) and neonatal wild type mice (Agt+/+). Within 2 minutes of being added to cardiac myocytes, angiotensin II activated MAP kinases and the response was completely blocked by pretreatment of the cardiac myocytes with CV-11974, a selective antagonist of angiotensin II type 1 receptors. Interestingly, mechanical stretch resulted in significantly greater activation of MAP kinases in Agt-/- cardiac myocytes than in Agt+/+ cardiac myocytes. CV-11974 failed to suppress the stretch-induced activation of MAP kinases in Agt-/- cardiac myocytes while it inhibited the activation in Agt+/+ cardiac myocytes. BQ123, an endothelin type A receptor antagonist, had no effect on stretch-induced activation of MAP kinases in cardiac myocytes from either mouse strain. These results suggest that cardiac RAS is important for stretch-induced MAP kinase activation in Agt+/+ cardiac myocytes; however, angiotensin II is not indispensable for mechanical stretch-induced activation of MAP kinases in Agt-/- cardiac myocytes.

Angiotensin II↗

PubMed1997

Sonodynamically induced antitumor effect of gallium-porphyrin complex by focused ultrasound on experimental kidney tumor.

The antitumor effect of a gallium-porphyrin complex, ATX-70, induced by focused ultrasound, on colon 26 carcinoma implanted in a mouse kidney was investigated. Colon 26 tumors were exposed to focused ultrasound at 500 kHz and 1 MHz in a progressive wave mode. Both frequency components were superimposed onto each other in the focal zone to efficiently produce cavitation in the tumor. ATX-70 was administered intravenously at the dose of 2.5 mg/kg, 24 h before the ultrasonic exposure. Antitumor effects were evaluated by histological observation 7 days after the exposure. The destruction of tumor tissue was observed with the ultrasonic treatment in combination with ATX-70, while neither the treatment with ATX-70 alone nor that with ultrasound alone caused any necrosis. These results first demonstrated that antitumor effects of a porphyrin compound can be induced by focused ultrasound in a progressive wave mode.

Animals↗

PubMed1997

Amino acid losses and nitrogen balance during slow diurnal hemodialysis in critically ill patients with renal failure.

OBJECTIVE: The effects of slow diurnal hemodialysis (slow HD) on amino acid losses and nitrogen balance were studied. DESIGN: Slow HD was conducted for 10 h during the day at the dialysate flow rate of 30 ml/min. The patients received total parenteral nutrition including 40 g of amino acids (6.08 g of nitrogen). The amino acid concentrations in plasma and dialysate were determined and the daily nitrogen balance was calculated from the urea nitrogen appearance. PATIENTS: Six critically ill patients with renal failure were entered into the study. RESULTS: Slow HD eliminated 48.5 +/- 4.4 mmol (6.2 +/- 0.6 g) of amino acids, representing 16% of the daily amino acid load. The estimated nitrogen balance was -2.3 +/- 1.3 g/day. Amino acid nitrogen lost in the dialysate was 1.0 +/- 0.1 g, contributing 43% of the daily negative nitrogen balance. CONCLUSION: The amount of amino acid losses during slow HD should be taken into consideration when designing nutritional schedules for maintaining positive nitrogen balance in critically ill patients.

Aged↗

PubMed1997

Effect of acetazolamide on cerebral blood flow and tympanic temperature in healthy subjects and patients with subacute subarachnoid haemorrhage.

The influence of the increased cerebral blood flow (CBF) induced by acetazolamide on tympanic temperature (Tty) was examined in three healthy male volunteers and in five patients with subacute subarachnoid haemorrhage (SAH). The CBF was estimated by means of stable xenon-enhanced computed tomography before and after the administration of acetazolamide. The Tty was recorded continuously in both ears using thermistor thermometers. In all subjects, CBF increased ranging from 11% to 108% after acetazolamide administration. In all the healthy subjects and in two patients with mild SAH, Tty was higher than the oesophageal temperature (Toes) and Tty decreased bilaterally, ranging from 0.07 to 0.35 degree C as CBF increased. Three patients with severe SAH were febrile, their Toes exceeding Tty and their Tty rose by 0.30 to 0.53 degree C with increased CBF. These observations suggest that Tty follows brain temperature which changes with an increase in CBF in euthermic subjects as well as in febrile subjects.

Acetazolamide↗

PubMed1997

Relationship between hepatic angiotensinogen mRNA expression and plasma angiotensinogen in patients with chronic hepatitis.

Recent association and linkage studies suggested that angiotensinogen may play an important role in the pathogenasis of essential hypertension. However, there is little information in human concerning a relationship between plasma angiotensinogen levels and the angiotensinogen mRNA expression in the liver, which is the main production site of angiotensinogen. Therefore, the aim of this study was to examine whether hepatic angiotensinogen gene expression determines the level of circulating angiotensinogen and the activity of the renin-angiotensin system in humans. The subjects were 36 patients with chronic hepatitis. Blood was collected from each patients for estimation of plasma renin activity, plasma angiotensinogen and angiotensin II concentrations and several parameters of liver function. In addition, total RNA was isolated from liver biopsy specimens, which were then used to measure angiotensinogen mRNA with Northern blot analysis. Levels of angiotensinogen mRNA were detected easily in the liver biopsy specimens in all of the patients. Hepatic angiotensinogen mRNA levels were positively correlated with plasma angiotensinogen levels (r=0.41, P=0.013). In contrast, hepatic angiotensinogen mRNA levels did not show any significant relationship with plasma renin activity, plasma angiotensin II concentration, histological subgroup of hepatitis, histological activity index and parameters of liver function tests. The present study demonstrated, for the first time, that hepatic angiotensinogen mRNA levels correlated with plasma angiotensinogen concentration in humans.

Adult↗

PubMed1997

Plasma angiotensinogen concentrations in obese patients.

A close relationship between obesity and hypertension has been recognized, and plasma angiotensinogen concentrations (p-AGT) have been reported to correlate with blood pressure (BP). However, little is known about AGT in obese patients with hypertension. To define the role of AGT in obese hypertension, we measured p-AGT in obese patients. The subjects were 42 obese patients diagnosed on the basis of a body mass index (BMI) of more than 25 kg/m2, and 21 sex- and age-matched nonobese patients, whose BMI was less than 25 kg/m2. The hypertensive patients had not previously received antihypertensive drugs. P-AGT (P < .05) and mean BP (P < .0001) was increased in the obese patients as compared with the nonobese patients. Positive correlations were observed between BMI and p-AGT, mean BP and p-AGT, and BMI and mean BP (all P < .05). However, after adjustment for blood pressure, p-AGT was not different between groups, and after adjustment a positive correlation remained only between BMI and mean BP. These results suggested the possible involvement of increased p-AGT in hypertension in obese patients, although this may be a secondary change to hypertension or obesity.

Adult↗

PubMed1997

Distribution of alpha 1B-adrenergic receptor mRNA expression along rat nephron segments.

Although several alpha-adrenergic receptor genes are expressed in the rat kidney, little information is available on their expression in the renal nephron segments. We investigated the distribution of alpha 1B-adrenergic receptor mRNA in rat nephron segments using reverse transcription and polymerase chain reaction (RT-PCR). The nephron segments of six- to eight-week-old male Sprague-Dawley rats were microdissected. Total RNA was prepared by the acid-guanidinium-phenol-chloroform method and used in the following RT-PCR assay. The PCR products were size-fractionated with electrophoresis, visualized with ethidium bromide staining and confirmed by Southern blot analysis. Because the PCR primers spanned an intron, the amplification product of the predicted size was considered to be from alpha 1B-adrenergic receptor cDNA and not from genomic DNA. The PCR products were detected in glomerulus (Glm), proximal convoluted and straight tubules (PCT, PST) and cortical and medullary thick ascending limbs of Henle (CTAL, MTAL). No signals were detected in cortical or medullary collecting ducts (CCD, MCD). Large signals were detected in the PCT, and PST, while small signals were found in the Glm, CTAL and MTAL. The alpha 1B-adrenergic receptor mRNA was detected for the first time in rat Glm, PCT, PST and TAL using RT-PCR. alpha 1BAR mRNA seems to be expressed in the specific sites along the nephron and may play significant roles in renal functions, although the specific physiological effects of the renal alpha 1B-adrenergic receptor are unknown.

Animals↗

PubMed1997

Characterization of bunazosin-sensitive alpha1-adrenoceptors in human renal medulla.

We studied the characteristics of bunazosin-sensitive alpha1-adrenoceptors in human renal medullae by using renal-clearance studies and radioligand-binding assay. In 12 patients with hypertension, renal-clearance studies demonstrated that bunazosin significantly increased renal blood flow from 683 +/- 82 (SD) to 829 +/- 103 ml/min (p < 0.05) and decreased renal vascular resistance from 0.18 +/- 0.02 to 0.14 +/- 0.02 mm Hg/(ml/min) (p < 0.05), but that prazosin had little effect on renal function. In a radioligand-binding assay, specific, saturable, and stereoselective [3H]bunazosin binding, with a single class of binding sites (Kd = 2.7 +/- 1.4 nM; Bmax = 44 +/- 16 fmol/mg protein; n = 11) was detected in membrane preparations of human renal medullae. The rank order of potency of antagonists that inhibited [3H]bunazosin-binding was bunazosin (Ki in nM = 49) > prazosin (57) > yohimbine (3,900) > propranolol (29,000), and that of agonists, l-norepinephrine (7,400) > l-epinephrine (19,000) > d-norepinephrine (71,000). The competition curves fit a one-site model. These findings suggest that bunazosin-sensitive alpha1-adrenoceptors exist in human renal medullae and participate in the regulation of renal hemodynamics.

Adrenergic alpha-1 Receptor Agonists↗

PubMed1997

In vitro and in vivo enhancement of sonodynamically active cavitation by second-harmonic superimposition.

Acoustic cavitation, the primary mechanism of sonochemical effects, is known to be induced more easily by standing waves than by progressive waves. It has been found that acoustic cavitation can be an order of magnitude enhanced by superimposing the second harmonic on the fundamental. Significant synergistic effects between the fundamental and the second harmonic were observed in both in vitro and in vivo experiments employing a progressive wave field. Second-harmonic superimposition induces in vitro sonochemical reaction as well as fractional harmonic emission at a relatively low ultrasonic intensity even in a progressive wave field. The effect of second-harmonic superimposition was also investigated using exteriorized mouse livers suspended in degassed saline. The intensity threshold for the production of focal tissue damage, paired with fractional harmonic emission was significantly lowered by second-harmonic superimposition especially when a sonodynamically active agent had been administered to the mouse. Insonation with second-harmonic superimposition in combination with such administration may have potential use for selective tumor treatment.

Acoustics↗

PubMed1997

Using acoustic radiation force as a concentration method for erythrocytes.

We investigated the potential damage inflicted on erythrocytes by acoustic radiation force when the cells are concentrated by a 500-kHz ultrasonic standing wave at the pressure node. The extent of the damage was estimated from the concentrations of potassium ions, iron complexes, and lactate dehydrogenase released from the cells. After 2 min of ultrasound irradiation at 12.8 mJ/m3, the cells concentrated on the pressure node, with a cell distribution half-width of 138 microns; no significant release of intracellular components was detected, even after 15 min of irradiation. The results indicate that even small ions like potassium are not released as a result of ultrasound irradiation on cell membranes without cavitation, and they demonstrate the potential use of acoustic radiation force for concentrating living cells in biomedical applications.

Acoustics↗

PubMed1997

Modulation of tissue angiotensinogen gene expression in genetically obese hypertensive rats.

Wistar fatty rats (WFR) show obesity and obesity-related features, including hypertension. In this study, we examined the expression of angiotensinogen mRNA in a variety of tissues at different times in WFR and control Wistar lean rats (WLR). WFR were obese and hypertensive at 16 and 24 wk. Plasma renin activity and plasma angiotensinogen concentration showed age-dependent increases in WFR but decreases in WLR. Northern blot analysis showed no significant differences in the levels of hepatic and renal angiotensinogen mRNA between WFR and WLR, and the levels of fat and adrenal angiotensinogen mRNA were lower in WFR than in WLR. On the other hand, the levels of cardiac angiotensinogen mRNA at 16 and 24 wk and those of aortic angiotensinogen mRNA at 16 wk were significantly higher in WFR than in WLR. These results show that the expression of tissue angiotensinogen mRNA is regulated differently in WFR and WLR and indicate that the development of hypertension in WFR is accompanied at least temporally with increases in plasma angiotensinogen concentration as well as in cardiac and aortic angiotensinogen mRNA. Moreover, these results suggest the existence of obesity hypertension-linked and tissue-specific regulation of angiotensinogen gene expression.

Angiotensinogen↗

PubMed1997

Effect of epinephrine on cAMP accumulation in cultured rat inner medullary collecting duct cells.

In a previous study we have reported the existence of alpha2- and beta-adrenoceptors in cultured rat inner medullary collecting duct (IMCD) cells. In this report, we examined the effect of epinephrine on intracellular adenosine 3',5'-cyclic monophosphate (cAMP) accumulation and evaluated whether alpha2-adrenoceptors interact with beta-receptors, vasopressin receptors, and prostaglandin (PG) E2 receptors by measuring cAMP generation. Epinephrine stimulated cAMP accumulation in a dose-dependent manner [half-maximal effective concentration (EC50) = 300 nM]. Rauwolscine (10 microM) enhanced epinephrine effects, shifting the dose-response curve for epinephrine to the left (EC50 = 120 nM); however, beta-antagonists inhibited epinephrine-induced cAMP accumulation. Epinephrine (10 microM) inhibited cAMP accumulation maximally induced by isoproterenol (10 microM); this effect was reversed by rauwolscine (10 microM). Epinephrine inhibited vasopressin (100 nM)-induced cAMP accumulation but failed to inhibit PGE2 (10 microM)-induced cAMP accumulation. We conclude that epinephrine acts as an alpha2- and beta-adrenoceptor agonist and that alpha2-adrenoceptors interact with beta-adrenoceptors and vasopressin receptors but not with PGE2 receptors on cAMP accumulation. This suggests that alpha2-adrenoceptors play a physiological role via interaction with different hormone receptors.

Adrenergic Agonists↗

PubMed1997

Angiotensin-converting enzyme gene I/D polymorphism and carotid plaques in Japanese.

To clarify the role of genetic factors in atherosclerotic plaque formation in the carotid artery and magnetic resonance imaging abnormalities in the brain, we investigated the association of these abnormalities with the angiotensin-converting enzyme (ACE) genotype. One hundred sixty-nine subjects (age, 59.2+/-0.8 years, mean+/-SE) admitted to our hospital for health checkups underwent brain magnetic resonance imaging to evaluate lacunar infarction. B-mode ultrasound examinations of the carotid arteries were performed to detect atherosclerotic plaque. The I/D polymorphism of the ACE gene was determined by the polymerase chain reaction method. Multivariate regression analysis was performed to assess the effects of the following variables on the presence of plaque, mean plaque thickness, and number of plaques: fibrinogen, sex, age, body mass index, mean blood pressure, glycosylated hemoglobin, LDL cholesterol, HDL cholesterol, hematocrit, and the D allele of the ACE gene. The frequency of carotid atherosclerotic plaque was significantly (P=.034) higher in subjects with the D allele than in those without this allele. However, the frequency of lacunar stroke was similar in these groups. A multivariate regression analysis showed that the presence of plaque was independently associated with the D allele (odds ratio=3.27, P=.016). However, mean plaque thickness and the number of plaques were not associated with the D allele. The D allele of the ACE gene may be involved in the presence of carotid plaque but not in the extent of this plaque or asymptomatic lacunar stroke in Japanese subjects.

Aged↗

PubMed1997

Angiotensin-converting enzyme gene polymorphism adds risk for the severity of coronary atherosclerosis in smokers.

To investigate the relation between the angiotensin-converting enzyme (ACE) gene polymorphism and acute coronary syndromes with respect to environmental factors, we analyzed the association of genotype with the coronary angiographic findings of patients with acute myocardial infarction or unstable angina pectoris, and we examined the linkage of each genotype with established risk factors for coronary artery disease. We determined the ACE genotype in 152 Japanese patients with acute coronary syndromes and 399 healthy individuals. The genotype distributions were not different between the two groups (P=.74, chi2 test). In the former group, coronary angiograms were evaluated by criteria based on the number of diseased vessels, the number of stenotic lesions (> or = 50%), and the relative abnormal arterial portion (extent index). Although the number of stenotic lesions was higher in patients with the DD genotype than in those with the ID or II genotype (P=.006), there were no differences in the number of diseased vessels or the extent index. When only smokers were analyzed, the number of diseased vessels (P=.032), number of stenotic lesions (P=.003), and extent index (P=.019) were all higher in patients with the DD genotype than in those with the ID or II genotype. In contrast, these differences in the respective parameters did not exist in nonsmokers. The results indicate smoking-associated effects of the ACE genotype on the severity of coronary atherosclerosis.

Coronary Artery Disease↗