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Biomedical subjects

H Iwao

Publications and source records attributed to H Iwao.

At least 163 records · Page 9Linked to original sources
PubMed1985

High-molecular-weight renin converting enzyme from dog kidney: detection and fractionation.

Renal cortical high-molecular-weight renin (Mw:60,000) of the dog is a complex of renin (low-molecular-weight renin; Mw:40,000) and a renin binding protein. We detected an enzyme-like substance that catalyzes the conversion from high- into low-molecular-weight renin. When the renal cortical extract was added to the high-molecular-weight renin and the preparation incubated at 37 degrees C for 30 min, the high-molecular-weight renin was converted into the low-molecular-weight form. No such conversion occurred in the case of renal medullary extract. This converting substance was fractionated using concanavalin A Sepharose, 70% ammonium sulfate saturation and DEAE-cellulose chromatography. The converting activity was inhibited by potassium tetrathionate, N-ethylmaleimide and 5,5'-dithiobis-(2-nitrobenzoic acid). These events suggest that this substance is an enzyme possessing sulfhydryl moieties. However, a cathepsin B inhibitor leupeptin did not affect the activity. Accordingly, the high-molecular-weight renin converting enzyme, which is sensitive to sulfhydryl oxidation, may explain the mechanism of interconversion between high- and low-molecular-weight renin involving the oxidation-reduction of tissue sulfhydryl groups.

Animals↗
PubMed1985

Direct estimation of cardiac reserve through analysis of relation between oxygen consumption and heart rate during exercise testing.

In order to elucidate fundamental relationship between exercise and cardiac reserve, we investigated the parameters of regression equation (VO2 = A X HR + B) between oxygen consumption (VO2 ml/kg/min) and heart rate (HR) during exercise test (Bruce). 62 male children were divided into 3 groups based on history and clinical evaluation. HR related linearly with VO2 (average r = 0.967, range 0.90-0.993). Both of the parameters A and [B] were significantly high in Athlete (A = 0.465 +/- 0.043, [B] = 36 +/- 6.07), low in Failed (0.297 +/- 0.055, 17.4 +/- 6.1) and middle in Ordinary group (0.366 +/- 0.078, 23.5 +/- 8.6) (p less than 0.005). Based on our result of linear VO2-HR relation, and on the previously reported studies that cardiac output linearly and consistently relates with VO2, we considered the meaning of the parameters as follows; A determines the possible maximum stroke volume (SV), and B determines the HR where SV reaches plateau. In conclusion, since the SV is considered as a measure of cardiac function, measuring the parameters of VO2-HR relation allows us to isolate cardiac functional reserve through the exercise tolerance test.

Adolescent↗
PubMed1985

Left ventricular diastolic pressure-volume and stress-strain relationship in children.

Diastolic pressure and volume (P-V) curves were approximately exponential and fitted the equation, dP/dV = aP + b, where a was left ventricular volume elastic constant. Stress and strain (sigma-epsilon) curves were expressed by the equation, d sigma/d epsilon = k sigma + c, where k was wall stiffness constant. These exponential curves have been fitted over the whole diastole, but theoretically, the mid-diastole should reflect diastolic elastic properties best. In the present study, therefore, special attention was paid to the mid-diastole in each patient, and both P-V and sigma-epsilon relationships were analyzed by fitting the data to the above mentioned curves during this period of time. This analysis was made in two separate groups of patients. One was the control group consisting of 2 patients with normal hearts, 2 patients with mild pulmonary stenosis, and 25 patients with post mucocutaneous lymph node syndrome. The other group consisted of patients with postoperative congenital heart disease, that is, 8 patients with atrial septal defect and 5 patients with tetralogy of Fallot. The elastic constant (a) could not be compared if the size of the hearts differed. The results of the present study, however, demonstrated that the size of the heart was closely related to the constant, a. In the control group, the constant (a) was exponentially related to the size of the heart, and expressed as follows: a = 0.30e-0.037EDV + 0.045 (r = 0.94, p less than 0.01) In contrast, the wall stiffness constant (k) was not related to the size of the heart. After surgical repair of congenital heart disease, the stiffness constant in the left ventricle was normal in patients with postoperative atrial septal defect, while it was significantly increased in patients with postoperative tetralogy of Fallot.

Cardiac Volume↗
PubMed1984

Ultrasonography and brain pathology of periventricular hemorrhage and subependymal cyst in the preterm neonate.

Ultrasound (US) findings in 32 premature infants with intraventricular hemorrhages (IVH, 21 cases), subependymal hemorrhages (SEH, 5 cases) or subependymal cysts (SEC, 6 cases) were reviewed to determine the accuracy of US diagnosis and clarify the pathogenesis of SEC. With single US there was the possibility of false-positive or -negative SEH or IVH, but serial US showed diagnostic accuracy for SEH or IVH. Four of 6 cases with iron-negative SEC did not show an image of prior SEH and the SEC suggested focal ischemic microcirculation which may be important in the pathogenesis of the occurrence of SEH or the development from SEH to IVH.

Brain↗
PubMed1984

Renin-angiotensin system in genetically hypertensive mice.

We investigated the renin-angiotensin system in the genetically hypertensive (HBP), normotensive (NBP) and low blood pressure (LBP) mice developed by G. Schlager, one of the authors. Renin in the plasma, kidney and submaxillary gland was determined by enzymatic assay and by direct radioimmunoassay (DRIA). Trypsinization of mouse plasma was also investigated. PRA and plasma renin content were not significantly different in the different lines, sexes and generations. Trypsinization of the plasma revealed the presence of inactive renin, as has also been found in humans, hogs, dogs and rats. The proportion of active renin against trypsinized total renin was about 54-77% and was not significant in the different lines, sexes and generations. There was also no significant difference in renal renin content in the various lines, sexes and generations. However, in the submaxillary gland, renin content and activity were high in male mice, in every line. These data suggest that the renin-angiotensin system may not contribute to the established phase of blood pressure.

Animals↗
PubMed1984

Physiological significance of the slope of the regression equation between oxygen consumption and heart rate in exercise testing.

The relationship between oxygen consumption (VO2) and heart rate (HR) was studied in 62 male children. Based on clinical evaluation and history, they were divided into three groups, i.e., athlete, ordinary and failed. There was a high linear correlation between HR and VO2 in each individual. The averaged values of the slope and standard deviations were 2.09 +/- 0.189 in the athlete group (n = 17), 2.60 +/- 0.140 in the ordinary group (n = 16) and 3.17 +/- 0.591 in the failed group (n = 29). The statistical differences were confirmed among the groups (p less than 0.005). The results suggested that the slope of the HR vs. VO2 relation was related to an inotropic state of cardiac function. We concluded that the slope was a more suitable and more direct evaluation of cardiac function during exercise. Moreover, the method was non-invasive and safe because it required no potentially hazardous maximum work load for the patients.

Child↗
PubMed1984

Renal metabolism in mice of exogenously administered 125I labelled renin.

125I labelled mouse submaxillary renin was administered intravenously to anaesthetized male Institute of Cancer Research, USA (ICR) mice in an attempt to determine the organ-related degradation of circulating renin. A specific antirenin antiserum was used for identification. The disappearance rate of labelled renin from plasma was estimated on the basis of a two-compartmental model. The mean half-time of clearance of labelled renin from plasma in intact control and 70% hepatectomized mice was 13.3 +/- 0.8 and 12.0 +/- 0.9 min respectively; these values were not significantly different. The mean half-time of clearance of labelled renin from plasma in nephrectomized mice was 40.0 +/- 2.4 min; this was significantly longer than intact controls and 70% hepatectomized mice. Fifty per cent of the administered renin accumulated in the kidney and 9% in the liver. A small amount of 125I labelled renin was identified in urine, and a large amount of 125I liberated from labelled renin was detected. Since the high performance liquid chromatography profiles showed that plasma renin rapidly moves into the kidney, clearance of circulating renin may take place mainly in this organ.

Animals↗
PubMed1983

Whole body autoradiographic distribution of exogenously administered renin in mice.

The distribution of exogenously administered renin was investigated using whole body autoradiography. Purified renin from mouse submaxillary gland (SR) was labeled with radioactive iodine (125I). This labeled renin (125I-SR) and Na125I were administered into the tail vein of male ddY mice, in doses of 10.2 and 16.4 mu Ci/30 g body weight, respectively. Mice were killed by an overdose of ether, and autoradiography was performed on whole body sections. To separate free 125I liberated from 125I-SR, sections were treated with perchloric acid. A major accumulation of 125I-SR, acid-insoluble, was evident in the renal cortex, whereas the hepatic accumulation of 125I-SR was minor. Radioactivity in the thyroid and submaxillary glands, in the stomach, and in urine was also apparent, but disappeared after acid treatment, except in the thyroid glands. Radioactivity in the brain, intestinal content, spleen, and adrenal glands was nil. These autoradiograms provide the first evidence that exogenously administered renin is mainly distributed in the renal cortex.

Animals↗
PubMed1983

Subcellular localization of exogenously administered renin in mouse kidney.

Our recent findings on the subcellular localization of exogenously administered 125I-labeled mouse submaxillary renin in the mouse kidney are summarized herein. 125I-labeled renin was given intravenously to anesthetized male ICR mice (6 weeks) in a dose of 20 ng (2 muCi)/40 g body weight and the subcellular distribution was identified by the reaction with a specific antiserum of the mouse submaxillary renin. 125I-labeled renin was identified mainly by differential centrifugation in the heavy mitochondrial fraction. With discontinuous sucrose density gradient centrifugation, the radioactivity was most readily detected with 1.2 M and 1.5 M sucrose. Over 90% of the radioactivity was identified in the form of 125I-labeled renin with a molecular weight of 38,000 daltons in each fraction. Light and electron microscopic autoradiography revealed that the 125I-labeled renin had accumulated in the apical region of the proximal convoluted tubular cells and was mainly located in the lysosomal granules. All these data taken together indicate that the exogenous renin filtered through the glomerular capillaries is reabsorbed and localized in the lysosomes of the proximal convoluted tubular cells.

Animals↗
PubMed1983

Effects of EDTA and verapamil on renin release in dogs.

EDTA or verapamil was infused into the renal artery of the anesthetized dog, and the effects on renin release and renal function were examined in an attempt to elucidate the role and action site of calcium ion in the renin secretory system. Both EDTA (25 mg/min) and verapamil (50 micrograms/min) increased RSR and RBF with a concomitant increase of urine flow, although there was no change in systemic arterial pressure. An infusion of verapamil in combination with ouabain produced a significant increase in RBF which was similar to that seen with verapamil alone. Urine flow and urinary excretion of electrolytes were also increased, but these changes did not differ from those seen with ouabain infusion alone. Ouabain alone did not affect RSR, but its infusion combined with verapamil resulted in a significant increase in RSR. Therefore, the effects of EDTA and verapamil on renin release may reflect the action of both drugs on the vascular component of the juxtaglomerular apparatus. If a change in calcium movement similar to the one in vascular smooth muscle occurs in the juxtaglomerular cells, the altered concentration of calcium may be considered to induce, in part, the stimulation of renin release by EDTA or verapamil.

Animals↗
PubMed1983

Renal effects of piretanide in dogs.

Effects of 4-phenoxy-3-(1-pyrrolidinyl)-5-sulfamoyl benzoic acid (piretanide, Arelix) on renal function and hemodynamics were investigated in anesthetized dogs by clearance, stop-flow and radioactive microsphere methods. Marked diuresis occurred within 10 min after intravenous injection of piretanide (0.01, 0.05 and 0.25 mg/kg) and it was accompanied b natriuresis. Piretanide (0.25 mg/kg) clearly inhibited the reabsorption of solute-free water during saline diuresis, suggesting that the drug acts in the ascending limb of Henle's loop. Stop-flow experiments revealed that sodium reabsorption was reduced by piretanide (0.25 mg/kg) at the distal tubule including the ascending limb of Henle's loop. Piretanide (0.25 mg/kg) caused a maximum increase of about 30% in renal blood flow at 10-15 min after the injection; within the renal cortex the increase in blood flow was greater in the juxtamedullary area than in the superficial area. The increased blood flow in the inner cortex conceivably resulted in a washout of the osmotic substances in the medulla and inhibited the concentrating mechanisms of the kidney. The effect of piretanide on intrarenal hemodynamics may also contribute to its diuretic action.

Animals↗
PubMed1982

Intrarenal localization of renin binding substance in rats.

Renin binding substance is a protein that reacts with renin (Mw:40,000) to form a high-molecular-weight renin (Mw:60,000). There is evidence that this substance is present in the renal cortex. However, the exact localization has not been determined. We now report that when glomeruli and tubular segments were isolated from the rat kidney cortex and were frozen and thawed to extract proteins, the high-molecular-weight renin was detected by high performance liquid chromatography, when renin was mixed with an extract of tubular segments, but was not detected with an extract of the glomeruli. Thus, the renin binding substance was demonstrated in the cortical tubular cells but not in the glomeruli. Thus, the renin binding substance was demonstrated in the cortical tubular cells but not in the glomeruli, and the renin binding substance probably does not contribute to the process of biosynthesis of renin in juxtaglomerular cells. Rather, this substance may play a role in tubular functions in the kidney.

Animals↗
PubMed1982

Sulphydryl oxidation in the mechanism of molecular-weight conversion of renin in dog kidney.

1. A high-molecular-weight renin (M(r) 60 000) was formed by the reaction of a low-molecular-weight renin (M(r) 40 000) with a renin-binding substance in canine renal cortical extract in the presence of the sulphydryl (SH) group oxidizing agent potassium tetrathionate; thus the reaction required SH oxidation. 2. Renin extracted from isolate renin granules was adsorbed on to thiopropyl Sepharose 6B, and then liberated with dithiothreitol (50 mmol/1), indicating that it possessed on SH moiety(s). 3. However, the renin was capable of reaction with the renin-binding substance even after its SH moiety (or moieties) was protected with 5,5'- dithiobis-(2-nitrobenzoic acid). 4. The high-molecular-weight renin was converted into the low-molecular-weight renin by incubation (37 degrees C, 15 min) with cytosol (soluble fraction) of renal cortex and liver. Such converting ability was diminished after the cytosol was treated with perchloric acid or potassium tetrathionate. 5. These results suggest that the reaction of renin with the renin-binding substances does not require disulphide bond(s) and that an enzyme-like substance which is sensitive to SH oxidation is involved in the conversion from the high molecular-weight renin into the low-molecular weight renin.

Animals↗