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Biomedical subjects

H Endou

Publications and source records attributed to H Endou.

At least 127 records · Page 7Linked to original sources
PubMed1990

Intranephron PGE2 production in stroke-prone spontaneously hypertensive rats.

To investigate whether intranephron prostaglandin E2 (PGE2) production in stroke-prone spontaneously hypertensive rats (SHRSP) differs from that in Wistar-Kyoto rats (WKY), we measured PGE2 accumulation rates in microdissected nephron segments from 4- to 6- and 12- to 14-wk-old male rats by radioimmunoassay. In both young and adult WKY, PGE2 accumulation was highest in the papillary collecting duct (PCD) and outer medullary and cortical collecting tubules, intermediate in the glomerulus (Glm), medullary and cortical thick ascending limbs of Henle's loop, and distal tubule, and negligible in the proximal tubule. PGE2 accumulation in adult WKY was severalfold higher than that in young WKY. PGE2 accumulation in adult and prehypertensive young SHRSP was significantly lower than that of respective WKY in most segments, whereas urinary PGE2 excretion was significantly higher in SHRSP than in age-matched WKY. Plasma arginine vasopressin concentrations in adult SHRSP were significantly higher than in WKY. PGE2 accumulation stimulated by 5 microM arachidonic acid was significantly lower in SHRSP than in WKY in most segments of young rats but was lower only in Glm and PCD of adult rats. PGE2 accumulation stimulated by 2 microM Ca2+ ionophore A23187 was significantly lower in most segments of adult and young SHRSP. These results indicate that a decrease in renal tubular PGE2 productive activities in SHRSP might not be caused by secondary adaptation to hypertension.

Aging↗
PubMed1990

Inhibitory effect of phorbol ester on sodium transport in frog urinary bladder.

To confirm the role of protein kinase C (PKC) on epithelial Na transport, we studied the effects of phorbol 12-myristate 13-acetate (PMA) and dioctanoylglycerol (DiC8), activators of PKC, on short-circuit current (Isc) in frog urinary bladder and further examined the influence of sphingosine, an inhibitor of PKC, on PMA- or DiC8-modulated Isc. PMA reduced basal Isc in a dose-dependent manner, and sphingosine (10 and 100 microM) partially restored PMA-reduced Isc. On the other hand, DiC8 (5 x 10(-5) M) also reduced basal Isc, and this action was completely prevented by 100 microM sphingosine. Both PMA (4 x 10(-5) M) and DiC8 inhibited vasopressin (50 mU/ml)- and forskolin (5 x 10(-5) M)-stimulated increases in Isc. PMA (4 x 10(-5) M) also inhibited 8-bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP)-stimulated increase in Isc. Furthermore, PMA (4 x 10(-5) M) and DiC8 (5 x 10(-5) M) inhibited vasopressin (50 mU/ml)-stimulated cAMP accumulation. DiC8 also inhibited forskolin-stimulated cAMP accumulation. These results indicate that PMA exerts inhibitory influence on Na transport mainly by its own potency of PKC activation. In addition, it is suggested that there is a cross talk in epithelial Na transport between PKC and cAMP-dependent pathway in frog urinary bladder.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1990

Furosemide acts on short loop of descending thin limb, but not on long loop.

In order to elucidate the tubular sites of action of loop diuretics such as furosemide, bumetanide and ethacrynic-cysteine complex within isolated rat descending thin limbs, cellular ATP was measured by luciferin-luciferase technique. When short descending thin limbs of Henle's loop (SDL) were incubated in the absence of exogenous substrate at 37 degrees C, cellular ATP content was decreased in a time-dependent manner (up to 49% after 60 min). This ATP decrease, however, was retarded significantly in the presence of loop diuretics at 60 min. The mean percentage of change in ATP compared with the control for each loop diuretic in SDL was as follows: 10(-5) M furosemide, 178%; 10(-5) M bumetanide, 189%; and 10(-7) M ethacrynic-cysteine complex, 154%; respectively. To the contrary, cellular ATP in long descending thin limb of Henle's loop (LDL) was not changed by loop diuretics compared with the control. A similar protection against ATP depletion was observed in the medullary thick ascending limb of Henle's loop, in which the mean percentage was as follows: 10(-5) M furosemide, 163%; 10(-5) M bumetanide, 187%; and 10(-7) M ethacrynic-cysteine complex, 134%. Similarly to LDL, the cellular ATP did not change in outer medullary collecting tubule. From these results, we conclude that loop diuretics act on the isolated rat SDL, but not on LDL.

Adenosine Triphosphate↗
PubMed1989

Biphasic increasing effect of angiotensin-II on intracellular free calcium in isolated rat early proximal tubule.

In the freshly isolated early proximal tubule (S1), the effect of angiotensin II (ANG II) on cytosolic Ca++ concentration ([Ca++]i) was determined using the fluorescent indicator fura-2. In order to establish an adequate experimental system, we investigated firstly the relationship between cellular ATP and [Ca++]i under various conditions in late proximal tubule, the most fragile nephron segment, and cortical collecting tubule, a relatively stable one. We found out that cellular ATP depletion caused [Ca++]i to rise, and ANG II response to [Ca++]i under high ATP condition was higher than that under low ATP condition. ANG II-induced [Ca++]i rise in S1 was biphasic, demonstrating the two peaks corresponding to the 10(-11) and 10(-7) M ANG II. This study suggests for the first time 1) the necessity of high intracellular ATP to evaluate a high affinity ANG II actions and 2) the biphasic characteristics of [Ca++]i increase by ANG II in intact S1.

Adenosine Triphosphate↗
PubMed1989

Inhibitory effect of cyclic AMP on phorbol ester-stimulated production of reactive oxygen metabolites in rat glomeruli.

Studies were conducted to investigate cross-talk between protein kinase C (PKC) and cyclic AMP (cAMP) pathways using rat glomeruli (Glm). Phorbol 12-myristate 13-acetate (PMA), a PKC activator, stimulated production of reactive oxygen metabolites (ROM) in Glm. Forskolin and dibutyryl cAMP (Bt2cAMP) inhibited production of ROM dose-dependently. In the presence of both Bt2cAMP and 3-isobutyl-1-methylxanthine (IBMX) an additive effect was observed. Forskolin at 10(-4) inhibited translocation of PKC from the cytosol to the membrane. These results demonstrate that cAMP-mediated inhibition can occur at a step distal to PKC activation.

1-Methyl-3-isobutylxanthine↗
PubMed1989

Nephrotoxicity assessment by measuring cellular ATP content. I. Substrate specificities in the maintenance of ATP content in isolated rat nephron segments.

To clarify the characteristics of cellular ATP synthesis in individual nephron segments for assessing nephrotoxicity of chemicals, cellular ATP content was measured by the luciferin/luciferase system under various conditions using intact nephron segments isolated from male Sprague-Dawley rats. Increasing the duration of collagenase treatment of kidney slices significantly lowered the cellular levels of ATP newly synthesized from 2 mM glutamine in PST at 37 degrees C over 30 min (p less than 0.01). The tubular incubation time significantly affected the cellular ATP content in the early and middle portions (S2) of the proximal tubule (p less than 0.05 and p less than 0.01, respectively) over 20 min and in the late proximal tubule over 10 min. Among numerous substrates tested, such as D-glucose, glutamine, pyruvate, DL-lactate, and beta-hydroxybutyrate, the substrate utilization for maintaining cellular ATP content was entirely variable according to each nephron segment. Pyruvate and glutamine were the best substrates in the proximal tubule. On the other hand, ATP production from glutamine was less than that from the other substrates in the distally located nephron segments: medullary and cortical thick ascending limbs of Henle's loop (MAL and CAL, respectively), distal tubule, cortical and medullary collecting tubules (CCT and MCT, respectively). In general, glucose, pyruvate, and lactate appear to be equivalent in maintaining ATP content in the distal segments of renal tubules. A monovalent cation ionophore, monensin, at 10 micrograms/ml decreased the cellular ATP content in MAL, CAL, and MCT significantly. Mercuric chloride (HgCl2) was used as a model compound to study nephrotoxicity by investigating its effects on cellular ATP metabolism in microdissected nephron segments. HgCl2 at 1 x 10(-6) M significantly decreased ATP content only in S2 (p less than 0.05), clearly demonstrating S2 to be the most sensitive segment within the nephron. These results indicate that measurement of cellular ATP content would be a useful method forecasting the intrarenal toxic site and potency of possible nephrotoxic chemical compounds.

Adenosine Triphosphate↗
PubMed1989

Nephrotoxicity assessment by measuring cellular ATP content. II. Intranephron site of ochratoxin A nephrotoxicity.

To clarify the nephrotoxic site and potency of ochratoxin A (OCTA), we measured cellular ATP contents in nine nephron segments incubated with or without OCTA in vitro. Cellular ATP contents of nephron segments isolated under stereomicroscopic observation after treatment of renal slices with 0.1% collagenase were measured by the microchemiluminescence method. OCTA decreased cellular ATP content in a dose-dependent manner. A concentration-response study of OCTA showed that the minimum concentration of OCTA needed to cause a significant decrease in ATP was 10(-8) M in the middle portion of the proximal tubule (S2; p less than 0.05) and 5 x 10(-4) M in the medullary collecting tubule (MCT; p less than 0.01). Among nine nephron segments, OCTA at 5 x 10(-5) M significantly decreased cellular ATP content in only S2 and the terminal portion of the proximal tubule (S3; p less than 0.01). ATP synthesis in mitochondria isolated from the renal cortex was significantly inhibited by 10(-6) M OCTA (p less than 0.05). Probenecid at 4 x 10(-4) M protected against the OCTA-induced cellular ATP decrease. These results suggest that OCTA might enter the plasma membrane in S2 and S3 through the organic anion transport pathway and inhibit mitochondrial oxidative phosphorylation. This newly established method would be applicable to evaluation of the intrarenal toxic site and potency of various chemical compounds.

Adenosine Triphosphate↗
PubMed1989

Furosemide directly stimulates prostaglandin E2 production in the thick ascending limb of Henle's loop.

Studies were conducted to investigate direct effects of loop diuretics on prostaglandin E2 (PGE2) production using microdissected nephron segments. At first, the effect of indomethacin on the diuretic response to furosemide was re-evaluated in anesthetized rats. Indomethacin significantly attenuated the diuretic, natriuretic and chloruretic effects of furosemide without significantly affecting inulin and p-aminohippurate clearance or filtration fraction. But, in nondiuretic states, indomethacin had no significant effects on these parameters. Furosemide, ethacrynic acid and bumetanide significantly increased PGE2 production in cortical and medullary thick ascending limbs of Henle's loop (P less than .001), but not PGE2 production in the cortical and outer medullary collecting tubules. The effect of furosemide on PGE2 production in CTAL was dose-dependent, and higher concentrations of of furosemide than 10(-6) M significantly increased PGE2 production. On the other hand, chlorothiazide showed no PGE2 productive stimulation in these four nephron segments. This study demonstrates that the enhanced PGE2 production in the thick ascending limb of Henle's loop by furosemide and other loop diuretics is one possible mechanism of these drugs.

Animals↗
PubMed1988

Epidermal growth factor in the mouse kidney: developmental changes and intranephron localizations.

The developmental changes in epidermal growth factor (EGF) have been studied in tissue homogenates, kidney slices, and microdissected nephron segments of the mouse. Immunoreactive EGF concentration per milligram of protein increased in the kidney by about 20-fold from 1 week to 3 weeks of life, reaching the highest levels between 5 and 7 weeks, and decreasing by 10 weeks of life. The time course of the changes was different from those of submaxillary and urinary EGF. Above 7 weeks of age, kidney EGF was higher in female than in male mice. Among various zones of the kidney (outer cortex, inner cortex, outer medulla I, II and papilla), the outer medulla I and II contained the highest quantities of EGF per gram of wet tissue. The highest EGF content per millimeter length was observed in the medullary and cortical thick ascending limbs of Henle's loop. The amounts exceeded by about 4.5-fold those found in glomeruli and in proximal convoluted and proximal straight tubules, and by about 3-fold those present in distal and collecting tubules. Unilateral nephrectomy resulted in no significant changes in EGF levels in the contralateral kidney. The results suggest that the ontogeny of kidney EGF is different from that of the EGF found in the submaxillary gland, and that there is nephron heterogeneity in EGF content.

Animals↗
PubMed1988

Isolation by monoclonal antibody of intercalated cells of rabbit kidney.

We produced a monoclonal antibody, gamma G6, that reacts only with one cell type in the connecting (CNT) and collecting tubules (CT) of rabbit kidney. The gamma G6 antibody-reactive cells revealed carbonic anhydrase activity, showing one of the characteristics of intercalated (IC) cells. Using immunoelectron microscopy, we demonstrated that IC cells in cortical CT consist of the gamma G6 antibody-reactive and non-reactive cells, whereas all IC cells in medullary CT were reactive with the gamma G6 antibody. We used a cell sorter to enrich this cell type from the isolated kidney cell suspension. When we measured hormone-sensitive adenylate cyclase (ACase) activities of the sorted cells, the presence of parathyroid hormone (PTH) and isoproterenol (ISO) almost doubled ACase activities when compared with the basal values; however, no additive effect of PTH and ISO was observed. They showed no calcitonin-sensitive ACase and negligible arginine vasopressin (AVP)-sensitive ACase. We suggest that the IC cells recognized by the gamma G6 monoclonal antibody possess a receptor(s) for PTH and/or ISO but not for AVP in the CNT and CT, although it remains to be clarified whether the reactivities to PTH and ISO in these cells originate from single or dual cells.

Adenylyl Cyclases↗
PubMed1988

Substrate specificity to maintain cellular ATP along the mouse nephron.

To evaluate substrate utilization along the mouse nephron, cellular ATP content was measured under various conditions by the luciferin-luciferase technique. Individual micro-dissected nephron segments were incubated in a modified Hanks' solution (pH 7.4) with or without each of the following substrates: D-glucose, DL-lactate, beta-hydroxybutyrate (HBA), and L-glutamine. ATP production from glucose was minimal in the early proximal tubule (S1), but was substantial in the late proximal tubule (S3). Glutamine and lactate were the preferred substrates in proximal tubules. In contrast, ATP production from glutamine was less than that from the other substrates in distal nephron segments, including medullary and cortical thick ascending limbs of Henle's loop (MTAL and CTAL), distal tubule including the connecting tubule (DT), and cortical and medullary collecting tubules (CCT and MCT). Lactate and HBA were preferred substrates for ATP maintenance in CTAL, MTAL, and DT. Glucose was the best substrate in CCT. In addition, the specific contribution of anaerobic metabolism to maintaining cellular ATP was low in MTAL and CTAL. On the other hand, the glycolytic capacity of CCT and MCT was high. The above results demonstrate the substrate requirements for maintaining cellular ATP content within specific nephron segments.

3-Hydroxybutyric Acid↗
PubMed1988

Contribution of purine nucleotide cycle to intranephron ammoniagenesis in rats.

To evaluate the contribution of the purine nucleotide cycle (PNC) in renal ammoniagenesis, ammonia production (AP) in cortical tubular suspensions and microdissected nephron segments of control and acidotic rats was determined using various amino acids, including glutamine (Gln) and aspartate (Asp). In the cortical tubular suspensions, the best substrate for ammoniagenesis was Gln (153.1 +/- 19.4 nmol.mg protein-1.15 min-1) followed by Asp (70.9 +/- 11.4). Metabolic acidosis resulted in a significant increase of AP only from Gln (316.5 +/- 36.1 nmol.mg protein-1.15 min-1, P less than 0.01 vs. control). Intranephron distribution of AP (pmol/mm or a glomerulus/15 min) from Gln showed that the first segment of the proximal tubule (S1) was highest in control (95.7 +/- 9.0), and its AP markedly increased in acidosis (221.6 +/- 8.3, P less than 0.001 vs. control). The most interesting and striking finding was that with Asp as a substrate, AP was maximal in S1 (165.0 +/- 32.8), with a value exceeding that from Gln. An adenylosuccinase inhibitor, 6-mercaptopurine (0.1 mM), significantly inhibited AP from Asp in S1 and S3, and from Gln in S1. On the contrary, a specific inhibitor of phosphoenolpyruvate carboxykinase, 3-mercaptopicolinate (0.1 mM), caused a significant decrease of AP from Gln, but not from Asp, in S1. From these results it could be concluded that AP via PNC can occur at high rates, especially in S1, only when Asp is present at high concentrations.

Amino Acids↗
PubMed1988

A two-site solid phase enzyme immunoassay for rat epidermal growth factor.

A sensitive and simple two-site enzyme immunoassay was developed for rat epidermal growth factor (rEGF), which was purified from male rat submaxillary glands. This system is based on the sandwiching of the antigen between anti-rat EGF IgG antibody coated on a polystyrene bead and anti-rat EGF Fab' antibody-linked peroxidase, whose activity was stable at 4 degrees C for 6 months. In this system, the rat EGF was detectable at a concentration of 2 pg/tube. No interference was observed by addition of human plasma. There was no cross-reactivity with mouse EGF, human EGF, or other substances with similar chemical structures.

Animals↗
PubMed1988

Functional heterogeneity of rat hepatocytes: predominance of aryl hydrocarbon hydroxylase activity in perivenular zone.

To elucidate the hepatic intralobular distribution of aryl hydrocarbon hydroxylase (AHH) activity biochemically, periportal (PP) and perivenular hepatocytes (PV) from male Sprague-Dawley rats were separated by a fluorescence-activated cell sorter after labeling the PP zone with fluorescein diacetate and the perivenular zone with fluorescein isothiocyanate. AHH activity was higher in PV than in PP. The enzyme activity was induced about 6-fold in hepatocytes of rats pretreated with 3-methyl-cholanthrene, and the induction was more prominent in PP than in PV. Neither phenobarbital pretreatment nor altered lipid content of the diet induced the change in the enzyme activity.

Animals↗
PubMed1987

Intranephron distribution of epidermal growth factor immunoreactivity in the mouse.

Using a specific and sensitive epidermal growth factor (EGF) radioimmunoassay, the distribution of EGF in mouse kidneys was studied. In five portions (outer cortex, inner cortex, outer medulla I, II, and papilla) of kidney slices, the outer medulla revealed the highest immunoreactive EGF (iEGF) per wet weight of tissue. In microdissected nephron segments, the predominant iEGF per millimeter length was observed in the medullary and cortical thick ascending limbs of Henle's loop compared with other segments. It became more apparent when expressed per milligram protein. Fluorescence microscopy showed prominent staining for EGF in the thick ascending limbs of Henle's loop. The significance of the nephron heterogeneity in EGF contents is discussed.

Animals↗