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Biomedical subjects

M Naitoh

Publications and source records attributed to M Naitoh.

At least 37 records · Page 2Linked to original sources
PubMed1999

Zonal heterogeneity in action of angiotensin-converting enzyme inhibitor on renal microcirculation: role of intrarenal bradykinin.

The present study examined the role of intrarenal bradykinin in angiotensin-converting enzyme inhibitor (ACEI)-induced dilation of renal afferent (AFF) and efferent arterioles (EFF) in vivo, and further evaluated whether ACEI-stimulated bradykinin activity differed in superficial (SP) and juxtamedullary nephrons (JM). Arterioles of canine kidneys were visualized with an intravital charge-coupled device camera microscope. E4177 (an angiotensin receptor antagonist, 30 microg/kg) dilated AFF and EFF in SP (15 +/- 3% and 19 +/- 5%) and JM (15 +/- 3% and 18 +/- 4%). Subsequently, cilazaprilat (30 microg/kg) caused further dilation of both AFF (29 +/- 4%) and EFF (36 +/- 4%) in JM, whereas in SP it dilated only EFF (29 +/-3%). Similarly, in the presence of E4177, cilazaprilat caused further increases in sodium excretion. This cilazaprilat-induced vasodilation and natriuresis was abolished by a bradykinin antagonist (N(alpha)-adamantaneacetyl-D-Arg-[Hyp3,Thi5,8,D-Phe7]b radykinin). In parallel with these results, cilazaprilat increased renal bradykinin content, more greatly in the medulla than in the cortex (5.7 +/- 0.4 versus 4.6 +/- 0.1 ng/g). Similarly, cilazaprilat elicited greater bradykinin-dependent increases of nitrite/nitrate in the medulla. In conclusion, zonal heterogeneity in renal bradykinin/nitric oxide levels and segmental differences in reactivity to bradykinin contribute to the diverse responsiveness of renal AFF and EFF to ACEI. ACEI-enhanced kinin action would participate in the amelioration of glomerular hemodynamics and renal sodium excretion by ACEI.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1998

Observer agreement in the detection of proximal caries with direct digital intraoral radiography.

OBJECTIVE: The aim of this study was to compare several values for consistency obtained by charged-coupled-device-based direct digital intraoral radiography with those obtained by conventional film-based radiography to evaluate observer agreement in determining the depth of proximal caries. STUDY DESIGN: A total of 93 proximal surfaces on radiologic images that were obtained by both the conventional film-based bite-wing technique and by direct digital intraoral radiography were evaluated by six observers. One of these observers also evaluated the same images six months after the initial evaluation. The kappa value, consistency ratio, agreement ratio, and Kendall's correlation coefficient were calculated for interobserver and intraobserver agreement. RESULTS: The overall kappa values for interobserver agreement were 0.439 and 0.424 in the direct digital system and the film-based radiography, respectively. The depth-related change of the values showed similar patterns in the two modalities for both interobserver and intraobserver agreement. CONCLUSION: The digital intraoral system resulted in no deterioration in observer agreement, and it presents no problems for clinical use with respect to the reliability of diagnosis.

Dental Caries↗
PubMed1998

New hormonal blockade strategies in cardiovascular disease.

The circulation is controlled by overlapping haemodynamic, structural and neurohumoral mechanisms. Many hormonal vasoactive substances, mostly derived from endothelial cells, are also growth regulators. Although neurohormonal systems are involved in normal physiological compensatory responses they often become maladaptive in conditions such as congestive heart failure. The success of blocking the renin angiotensin system by angiotensin converting enzyme (ACE) inhibitors has led to efforts to block other hormonal systems. Neutral endopeptidase (NEP), the major enzymatic pathway for degradation of natriuretic peptides, has a similar catalytic site to ACE. This has led to compounds that simultaneously inhibit both enzymes. Such dual ACE/NEP inhibitors show promise in experimental hypertension and heart failure. Similar dual NEP/ECE (endothelin converting enzyme) inhibitors are becoming available. The hormone vasopressin has dual actions on the vasculature and the kidney via specific membrane receptors. Specific orally active vasopressin receptor antagonists have been developed and their therapeutic potential in hypertension, heart failure and oedematous states are being explored.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1998

Extreme right lobar atrophy of the liver: a rare complication of autoimmune hepatitis.

Lobar atrophy is a rare morphologic change of the liver. We describe a 73-year-old woman with mild liver dysfunction and history of Sjögren's syndrome who had right hepatic lobar atrophy. Serum biochemistry levels were as follows: albumin, 4.5 g/dl; total bilirubin, 1.0 mg/dl; alanine aminotransferase, 25 international units/l; aspartate aminotransferase, 27 international units/l; alkaline phosphatase, 333 international units/l; and gamma-glutamyl transpeptidase, 332 international units/l. Serological data were as follows: rheumatoid factor, 27.9; anti-nuclear antibody, 1:640; and antismooth muscle antibody, 1:80. Viral markers for hepatitis B were all negative. Anti-hepatitis C virus (anti-c-100) was negative. Portal hypertension developed thereafter, and the patient died of hepatic failure at age 76. Postmortem examination revealed autoimmune hepatitis with moderate fibrosis, portal vein thrombus, and complete obstruction of the right hepatic duct due to hepatolithiasis. Terminal hepatic failure resulted from combination of decreased hepatic volume due to the right lobar atrophy, exacerbation of autoimmune hepatitis in the remnant left hepatic lobe, decreased portal venous blood flow due to thrombosis, portal hypertension, and cholangitis with hepatolithiasis. This is the first reported case of hepatic lobar atrophy due to autoimmune hepatitis. From a clinical standpoint, patients with hepatic lobar atrophy, even if asymptomatic, should be followed up with careful attention to progression of liver diseases, portal hypertension, and biliary complications.

Aged↗
PubMed1998

Thirst in elderly subjects.

The hormonal changes associated with ageing, the occurrence of other medical condition and the use of medications increases the likelihood of conditions such as hyper- and hypo-natremia. Awareness of the homeostatic changes with age and the relations with disease and drugs will lead better management of fluid disorders in the elderly patient and hopefully a reduction in morbidity and mortality.

Aging↗
PubMed1998

Mechanism of progression of renal disease: current hemodynamic concepts.

BACKGROUND: Hypertension, a known independent risk factor for end-stage renal failure, damages the kidney in multiple ways. It produces hemodynamic and mechanical stress, which may lead to glomerular endothelial dysfunction. Both of these mechanisms may lead to increased glomerular leakiness, hence proteinuria, which may damage the kidney further. Hypertension may also stimulate the production of vasoactive substances that, in turn, activate the production of cytokines and growth factors, leading to the production of extracellular matrix proteins. Thus, the progression of renal failure is related to both systemic and glomerular hemodynamic changes and to the activation of vasoactive hormones, growth factors and cytokines. THERAPY: To protect the kidney, we need to control or prevent the occurrence of these factors. Therapy with effective antihypertensive agents, such as angiotensin-converting enzyme inhibitors, has been shown to slow the progression of end-stage renal disease.

Animals↗
PubMed1997

Role of kinin and renal ANG II blockade in acute effects of ACE inhibitors in low-renin hypertension.

In conscious deoxycorticosterone acetate (DOCA) salt-hypertensive dogs, the angiotensin-converting enzyme (ACE) inhibitors captopril and imidaprilat significantly decreased mean arterial pressure (MAP) and significantly increased urine flow rate, effective renal plasma flow (ERPF), glomerular filtration rate, and urinary sodium excretion. However, the angiotensin type 1 (AT1) receptor antagonist losartan caused a significant increase only in urinary sodium excretion without significant changes in MAP, urine flow rate, ERPF, and glomerular filtration rate. Simultaneous infusion of a bradykinin receptor antagonist inhibited the ACE inhibitor-induced reduction in MAP and increase in ERPF. DOCA salt treatment markedly suppressed plasma angiotensin II (ANG II) concentration (P < 0.001), although it decreased renal ANG II content only slightly (P < 0.05). Comparison of the expression of renal AT1 receptor mRNA in control kidneys with that in DOCA salt-hypertensive kidneys revealed no significant change. These results suggest that, in low-renin hypertension, inhibition of the relatively maintained ANG II production in the kidney participates in the natriuretic action of ACE inhibitors. However, hypotensive and other renal effects are mainly due to the action of bradykinin.

Angiotensin II↗
PubMed1997

Modulation of genetic hypertension by short-term AVP V1A or V2 receptor antagonism in young SHR.

To characterize the role of arginine vasopressin (AVP) V(1A) or V2 receptors and the possible interaction with the renin-angiotensin system in the pathogenesis of hypertension in spontaneously hypertensive rats (SHR), young male SHR were treated from 6 to 10 wk of age with AVP V(1A) receptor blockade, angiotensin-converting enzyme (ACE) inhibition, combination of V(1A) receptor blockade and ACE inhibition, V2 receptor blockade, and vehicle. Treatments were then withdrawn, and systolic blood pressure (SBP) was measured until 19 wk of age. At both 10 and 19 wk of age, SBP was significantly reduced with V(1A) receptor blockade, ACE inhibition, and combined treatment compared with vehicle treatment, although no treatment normalized SBP to levels of Donryu normotensive rats. Throughout the experimental period, no significant additive effects were observed with combined treatment. At 10 wk of age, plasma AVP concentration and 24-h urinary AVP excretion were increased with AVP V2 receptor blockade. At 19 wk of age, SBP was significantly higher in rats previously treated with V2 receptor blockade (233 +/- 3 mmHg) than with vehicle (221 +/- 2 mmHg) (P < 0.01). Left ventricular mass was significantly reduced in rats previously treated with ACE inhibition or combined treatment. These results suggest that AVP (via V(1A) receptors) and angiotensin II contribute to the pathogenesis of SHR hypertension, whereas the AVP V2 receptor may be involved in preventing the full expression of the hypertension, in male SHR.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1997

Rationale and pharmacology of angiotensin II receptor antagonists: current status and future issues.

BACKGROUND: The renin-angiotensin system consists of a cascade of substrate-enzyme interactions that culminates with the production of angiotensin II, the active peptide responsible for all the known effects of the renin-angiotensin system. Blocking this enzymatic cascade has been the focus of considerable research to the extent that the renin-angiotensin system is implicated in the control of blood pressure, sodium and water homeostasis, and cardiovascular function and structure. ANGIOTENSIN CONVERTING ENZYME INHIBITORS: Angiotensin converting enzyme (ACE) inhibitors provide one way of blocking the renin-angiotensin system, and to this end the compounds have proved efficacious in the treatment of hypertension and cardiovascular disease. However, these compounds are limited in the extent to which they block the renin-angiotensin system, partly due to recently described alternate pathways for the genesis of angiotensin II and also because ACE is not a very specific enzyme and has multiple other potential substrates including bradykinin, tachykinins, neurotensin substance P, and others. ANGIOTENSIN II RECEPTORS: The development of angiotensin II receptor antagonists represents a new way to block the renin-angiotensin system at the receptor level. Irbesartan is a new angiotensin II receptor antagonist that provides specific and insurmountable antagonism of the AT1 receptor subtype, demonstrating a greater than 8500-fold specificity for the AT1 receptor, the subtype which mediates all the known actions of angiotensin, compared to the AT2 receptor. Comparative studies have demonstrated that irbesartan is 10 times more potent than losartan and slightly more potent than E3174, losartan's active metabolite. Preclinical pharmacological studies in a variety of animal models have demonstrated that irbesartan provides a dose-dependent, insurmountable blockade of angiotensin and reductions in blood pressure, urinary protein and glomerular sclerosis score.

Angiotensin Receptor Antagonists↗
PubMed1996

Mediastinal yolk sac tumor in a young girl: case report and review of the literature.

The authors report a rare case of a female infant who underwent successful treatment of a mediastinal yolk sac tumor. Therapy included four cycles of preoperative PVB (cisplatinum, vinblastine, bleomycin), complete surgical resection of the tumor, and one postoperative cycle of PVB and four cycles of VAC (vincristine, actinomycine, cyclophosphamide) chemotherapy. The successful treatment of this tumor depends on preoperative chemotherapy to reduce the size, followed by complete surgical excision with subsequent postoperative chemotherapy. Recent improvements in the treatment of mediastinal yolk sac tumors are discussed.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1996

Role of adenosine in the renal responses to contrast medium.

Despite the development of non-ionic radiographic contrast media (CM), CM-induced nephropathy is a clinically important problem in patients with pre-existing renal insufficiency. We examined the effects of non-ionic CM (iohexol) on renal function in conscious dogs with and without renal insufficiency, and evaluated the effects of a non-selective (theophylline), an A1 selective (KW-3902), and an A2 selective adenosine antagonist (KF17837) on the renal responses to CM. In sham-operated group, iohexol (2 ml/kg/min for 3 min) increased effective renal plasma flow (ERPF) and glomerular filtration rate (GFR), whereas in renal insufficiency group (with subtotal nephrectomy), following transient increases in ERPF and GFR, CM markedly decreased ERPF (-46.5 +/- 6.7%) and GFR (-51.2 +/- 7.1%). In sham-operated group, theophylline and KF17837 markedly attenuated CM-induced increases in ERPF and GFR, while KW-3902 had no effects on CM-induced increases in ERPF or GFR. In renal insufficiency group, initial increases in ERPF and GFR were blunted by theophylline and KF17837. In contrast, the subsequent decreases in ERPF and GFR were attenuated by theophylline (% delta ERPF, -12.2 +/- 3.2% vs. -46.6 +/- 6.7%, P < 0.01; % delta GFR, 4.3 +/- 2.5% vs. -51.0 +/- 7.1%, P < 0.01), and were completely prevented by KW-3902 (% delta ERPF, 10.8 +/- 2.9%; % delta GFR, 23.8 +/- 4.4%), whereas KF17837 aggravated ERPF (-73.3 +/- 5.3%) and GFR (-78.4 +/- 5.3%). These data indicate that in normal renal function, iohexol elicits renal vasodilation by activating mainly the adenosine A2 receptors. In contrast, in impaired renal function, CM induces both A2 and A1 activation; the former is associated with the initial renal vasodilation, while the latter is responsible for the sustained aggravation of renal hemodynamics.

Adenosine↗
PubMed1996

Intestinal motility after massive small bowel resection in conscious canines: comparison of acute and chronic phases.

To evaluate intestinal function after 80% massive distal small bowel resection (MSBR), we continuously monitored interdigestive and postprandial bowel motility using bipolar electrodes and/or contractile strain gauge force transducers in conscious beagle dogs before and at 2-4 weeks (acute postoperative phase; acute phase) and 8-13 months (chronic postoperative phase; chronic phase) after the surgery. Fasting duodenal migrating myoelectric (or motor) complexes (MMC) occurred at longer intervals in the acute phase after 80% MSBR than in control beagles. Intervals between duodenal MMC in the chronic phase were similar to those found in control beagles. MMC arising from the duodenum were often interrupted before the jejunum above the anastomosis in the acute phase, and a slight recovery of propagation frequency to the jejunum above the anastomosis was observed in the chronic phase. However, duodenal MMC did not migrate smoothly to the terminal ileum in both groups. In the acute phase, the velocity of duodenal MMC propagation was slowed in every intestinal segment, including the duodenum and the jejunum above the anastomosis, and had not recovered even long after the operation. The duration of the postprandial period without duodenal MMC was prolonged significantly in the acute phase postoperatively. Although it shortened in the chronic phase, it still remained significantly longer than in controls. These findings suggest that changes in gut motility after MSBR tend to compensate for the shorter intestine and maintain small bowel absorption early postoperatively. However, these compensatory changes decrease over the long term, and their adaptive contributions to increased intestinal absorption may decrease as well.

Anastomosis, Surgical↗
PubMed1996

[Coagulation disorders as early predictor of brain injury].

To identify early prognostic value of brain injury, a comparison was made between computerized tomography (CT) findings, coagulation abnormalities, and clinical features in 51 patients with closed head injury. The patients were divided into three groups according to their plasma level of fibrin-fibrinogen degradation product (FDP): normal group (FDP 10 micrograms/ml or less) in 20 patients; moderately abnormal group (FDP 10-40 micrograms/ml) in 15 patients; and highly abnormal group (FDP 40 micrograms/ ml or more) in 16 patients. Cases with a fatal clinical course were mostly associated with very high FDP level. Mortality rate in the highly abnormal group was 44% and 7% in the moderately abnormal group were dead cases, while no cases in the normal group turned out poor outcome. Injury severity, as assessed by Glasgow Coma Scale (GCS) score, correlated with the increase of plasma FDP level. Although severe head injury (GCS 8 or less) was found in 44% of the highly abnormal group and 13% of the moderately abnormal group, normal group only had one case (5%). Very high FDP concentrations were found to be associated with combined hemorrhagic lesions and mass effect on CT scan, but not with a specific localization of brain damage. In summary, the evaluation of coagulation and fibrinolytic function in patients following closed head injury might have both diagnostic and prognostic value.

Adolescent↗
PubMed1995

Effects of selective vagotomy on circadian rhythms of plasma glucose, insulin and food intake in control and ventromedial hypothalamic (VMH) lesioned rats.

Effects of hepatic and celiac vagotomy on circadian rhythms of plasma glucose, insulin, and food intake were examined in sham-operated (control) and ventromedial hypothalamic (VMH) lesioned rats. Rats were acclimated to the condition with a 12-hour light-dark cycle for 1 week before surgery. One week after VMH lesions, control and VMH lesioned rats were divided into three groups: sham vagotomy, hepatic vagotomy, and celiac vagotomy. Three days after vagotomy, food intake was measured at 6-hour intervals. Seven days after vagotomy, plasma glucose and insulin were measured at the midpoint of each feeding period. In control rats, hepatic vagotomy destroyed circadian rhythms of plasma glucose and insulin probably due to removal of afferent function. In VMH lesioned rats, celiac vagotomy destroyed circadian rhythm of food intake due to the reduction of plasma insulin by removal of efferent function without affecting the loss of circadian rhythms of plasma glucose and insulin.

Afferent Pathways↗