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Biomedical subjects

M Kuramochi

Publications and source records attributed to M Kuramochi.

At least 73 records · Page 4Linked to original sources
PubMed1992

Angiotensin II does not increase renal prostaglandin E2 in response to pressure reduction.

Whether angiotensin II (Ang II) stimulates renal secretion of prostaglandin E2 (PGE2) synthesized in response to pressure reduction was examined. PGE2 and Ang II in aortic and renal venous plasma were measured before and during renal arterial constriction in anesthetized dogs, with or without an intrarenal arterial infusion of an Ang II antagonist, losartan potassium (1 mg/min), or saralasin (3 micrograms/min). In other anesthetized dogs, two doses of Ang II (30 and then 300 ng/min) were infused into the renal artery, and plasma Ang II levels and renal PGE2 secretion were measured. When renal perfusion pressure was reduced to 75 and 45 mm Hg by constriction, the renal secretion of PGE2 increased seven- and fourfold, respectively. Ang II levels in the renal venous plasma increased from 6.6 +/- 1.8 to 21.7 +/- 7.4 and then 48.1 +/- 15.3 pg/ml (both P less than 0.05) as the pressure decreased. Neither losartan nor saralasin suppressed the response of renal PGE2 secretion to the pressure reduction. The intrarenal infusion of Ang II (30 ng/min) elevated the Ang II level in the renal venous plasma from 9.8 +/- 4.6 to 33.7 +/- 4.2 pg/ml (P less than 0.01), but did not increase PGE2 secretion. The higher dose (300 ng/min) of Ang II increased it, but the Ang II level in the renal venous plasma was 166 +/- 63 pg/ml. These results suggest that the greater part of the increased renal synthesis of PGE2 in response to pressure reduction is not mediated by Ang II.

Angiotensin II↗
PubMed1992

Effects of dietary salt on sodium-calcium exchange and ATP-driven calcium pump in arterial smooth muscle of Dahl rats.

AIM: To compare the effects of dietary salt on sodium-calcium exchange and the ATP-driven calcium pump in arterial smooth muscle between Dahl salt-sensitive (DS) and salt-resistant (DR) rats. METHODS: Aortic rings freshly excised from 16 DS rats and 16 DR rats on a low- (0.3%) or high- (8%) NaCl diet for 4 weeks were superfused with physiological saline and isometric tension was measured. In the presence of 10 mumol/l phentolamine, 10 mumol/l verapamil and 5 mmol/l caffeine, relaxation of a low-Na+ contraction was promoted by external calcium removal. RESULTS: On the high-salt diet, the rate of relaxation at 1.2 mmol/l extracellular sodium (calcium extrusion by calcium ATPase) was significantly lower in aortic rings from DS rats than from DR rats. The increase in the rates of relaxation from 1.2 mmol/l to normal (139.2 mmol/l) extracellular sodium (calcium extrusion by sodium-calcium exchange) was significantly greater with the high-salt diet than with the low-salt diet in rings from DR rats, but it was not different between the high- and low-salt diets in DS rats. The rate of increase in tonic tension by reducing extracellular Na+ from normal to 1.2 mmol/l in the presence of verapamil, caffeine and phentolamine (calcium entry by sodium-calcium exchange) was significantly lower in rings from DS rats than in those from DR rats on the high-salt diet. CONCLUSIONS: These observations suggest that the effects of dietary salt on the sodium-calcium exchange system in arterial smooth muscle differ between DS and DR rats and that calcium extrusion by the calcium pump is decreased in DS rats compared with DR rats. The lack of an increase in sodium-calcium exchange in salt-fed DS rats might lead to an elevation in cellular calcium and contribute to the mechanism of hypertension.

Adenosine Triphosphate↗
PubMed1992

Sodium and noradrenaline in cerebrospinal fluid and blood in salt-sensitive and non-salt-sensitive essential hypertension.

1. The effects of dietary sodium on blood pressure and levels of sodium, other electrolytes and noradrenaline (NA) in the cerebrospinal fluid (CSF) and blood of 15 patients with essential hypertension were studied. The CSF and blood sampling was carried out after 7 days of a high salt intake (16-18 g/day) and after 7 days of a low salt intake (1-3 g/day). 2. Blood pressure and sodium concentrations in CSF and serum were significantly higher in the high salt period than the low salt period (CSF Na+ concentration: 147.7 +/- 0.4 mmol/L vs 145.3 +/- 0.5 mmol/L; P less than 0.001). Levels of CSF pressure and potassium or calcium concentrations were not different between the two periods. Plasma NA and plasma renin activity (PRA) were lower and CSF NA levels tended to be lower in the high salt period. 3. The levels and the changes in sodium and NA in CSF were not significantly different between the salt-sensitive (n = 8) and the non-salt-sensitive (n = 7) subjects, but the changes in plasma NA and PRA were smaller in the salt-sensitive subjects. 4. These results indicate that the sympathetic nervous system is less suppressed in salt-sensitive subjects during high salt intake. This may be due to altered neural responsiveness to sodium loading rather than being greater increases in sodium concentration in the central nervous system.

Adult↗
PubMed1992

Intracellular free magnesium of red blood cells in patients with renal disease.

While serum magnesium (Mg) level is increased in patients with end-stage renal disease (ESRD), it is decreased in renal transplant recipients (TR) receiving ciclosporin. This study was performed to examine the cation metabolism of red blood cells (RBC) in these patients. Intracellular free Mg was measured with 31P-nuclear magnetic resonance spectrometry, and ouabain-sensitive sodium (Na) efflux rate (Eos) was measured from the increase in RBC-Na concentration when RBC were incubated in the presence of ouabain. The ouabain-sensitive Na efflux rate constant (ERCos) was obtained by dividing Eos by RBC-Na concentration. RBC free Mg and ERCos were significantly higher in the TR group than in the ESRD group. There was a significant correlation between RBC free Mg and ERCos (r = 0.474, p less than 0.01). These results support the views that the regulation mechanism for intracellular free Mg is different from that for extracellular Mg in patients with renal disease, and intracellular free Mg modulates Na pump activity of RBC.

Adenosine Triphosphate↗
PubMed1992

Acute depressor effect of alcohol in patients with essential hypertension.

To investigate the time course of the effects of alcohol on blood pressure, we studied the response of ambulatory blood pressure, neurohumoral variables, and hemodynamics to a single moderate dose of alcohol in hypertensive patients. Sixteen Japanese men (22-70 years old) with essential hypertension who were habitual drinkers were examined under standardized conditions. On the alcohol intake day, they ingested 1 ml/kg ethanol (vodka) at dinner, and on the control day they consumed a nonalcoholic beverage. The order of the two periods was randomized. Mean ambulatory blood pressure was lower in the alcohol intake period than in the control period (125 +/- 3/74 +/- 2 versus 132 +/- 4/78 +/- 2 mm Hg, p less than 0.05), and the significant depressor effect of alcohol lasted for up to 8 hours after drinking. Blood pressure on the next day did not differ with or without alcohol intake. The acute hypotensive effect of alcohol was associated with an increase in heart rate and cardiac output and with a decrease in systemic vascular resistance as determined by echocardiography. Plasma catecholamine levels and renin activity rose significantly at 2 hours after dinner, whereas vasopressin and potassium levels fell on the alcohol day. Blood glucose and serum insulin levels were comparable between the two periods. Three patients with marked alcohol-induced flush had greater hypotensive and tachycardiac responses than those who did not show an alcohol-induced flush. The change in mean blood pressure induced by alcohol was negatively correlated with age, the baseline blood pressure, and the change in plasma norepinephrine. These results indicate that the major effect of acute alcohol intake is to lower blood pressure through systemic vasodilatation in hypertensive subjects. Ambulatory blood pressure monitoring may be useful for assessing blood pressure in habitual drinkers.

Adult↗
PubMed1992

Critical degree of renal arterial stenosis that causes hypertension in dogs.

The minimum degree of renal arterial stenosis needed to cause hypertension was identified by renal arterial angiography of anesthetized dogs. The effects of renal nerves and prostanoids on the critical stenosis were also examined. The left renal artery was constricted concentrically by a radiolucent constrictor device, and the stenosis of the artery was evaluated by cineangiography with the kidney either innervated or denervated. At this time, renal blood flow, renal perfusion pressure, and systemic blood pressure were serially monitored. In another group of dogs, renal venous and aortic blood samples were taken as the stenosis increased; these were assayed for prostaglandin E2 and plasma renin activity. The same experiments were done again after treatment with a cyclooxygenase inhibitor, aspirin DL-lysine (54 mg/kg). With the kidney either innervated or denervated, systemic blood pressure began to increase when the stenosis was more than 70% of the diameter of the renal artery; the renal blood flow decreased when the stenosis was more than 75% of the diameter. Aspirin treatment attenuated the increase in blood pressure but did not affect the autoregulation of the renal blood flow when stenosis was 70% or less. Prostaglandin E2 production increased in the stenotic kidney when the stenosis was more than 70%; aspirin inhibited prostaglandin synthesis and suppressed the stimulation of renin release. These results suggest that whether there is innervation or not, the critical degree of renal arterial stenosis that causes hypertension is more than about 70% of the diameter in the presence of renal prostaglandins; in their absence, the critical point above which hypertension occurs is 75% or more.

Animals↗
PubMed1992

Vascular responsiveness to angiotensin II and phenylephrine, the tubular function and the prostaglandin, renin-angiotensin system in a patient with Bartter's syndrome.

In a 39-yr-old female patient with Bartter's syndrome, vascular responsiveness to angiotensin II and phenylephrine was studied. Pressor responses to angiotensin II and to phenylephrine were markedly decreased prior to treatment and were improved by administration of indomethacin, dextran, KCl, captopril, propranolol or pindolol. Moreover, the responses of total peripheral vascular resistance to angiotensin II and phenylephrine were markedly decreased before treatment and were improved by the treatment. A relatively low fractional distal chloride reabsorption was found, and that was not changed after the administration of KCl or indomethacin. The results of this patient were compatible with the primary cause of Bartter's syndrome, defective chloride reabsorption at the loop of Henle, but the possibility of an abnormality in the vascular wall could not be denied.

Adult↗
PubMed1992

Changes in coagulation factors by passage through a dextran sulfate cellulose column during low-density lipoprotein apheresis.

To determine the extent of adsorption of coagulation factors by a dextran sulfate cellulose column used for selective removal of low-density lipoprotein (LDL), various coagulation factors were measured before and after application to the column during LDL apheresis. The column almost completely adsorbed many coagulation factors. Although the bradykinin concentration was markedly increased by passing the plasma through the column, this increment was suppressed by nafamostat mesilate which inhibits the initial contact phase of the intrinsic coagulation pathway. The von Willebrand factor, which forms a complex with factor VIII in plasma, is reduced in apheresis with nafamostat mesilate to the same extent as in apheresis without nafamostat mesilate. Thus, coagulation factors seem to be adsorbed by different mechanisms which include activation of the initial contact phase by the negative charges of dextran sulfate and concomitant adsorption with the phospholipid portion of lipoproteins containing apolipoprotein B or with von Willebrand factor.

Adolescent↗
PubMed1991

Glomerular hypertension in renovascular hypertensive patients.

Split intrarenal hemodynamics in stenotic and contralateral kidneys of unilateral renovascular hypertension (RVH) were estimated by Gomez's formulae. Forty patients with essential hypertension and 40 patients with RVH were studied. Split para-amino hippurate and inulin clearances were measured by ureteral catheterization as indexes for effective renal plasma flow and glomerular filtration rates, allowing the estimation of intrarenal hemodynamics such as afferent arteriolar resistance (RA), efferent arteriolar resistance (RE) and glomerular hydrostatic pressure (PG) in each kidney. Normal values of intrarenal hemodynamic parameters were obtained in 24 normotensive subjects without ureteral catheterization, assuming each kidney had the half function of both kidneys. Systemic mean arterial pressure did not differ between essential and renovascular hypertension (141 +/- 3 vs. 148 +/- 3 mm Hg). Effective renal plasma flow and glomerular filtration rates were decreased in the stenotic kidney of RVH (98 +/- 8, 24 +/- 2 ml/min/m2), while increased in the contralateral kidney (195 +/- 11, 48 +/- 2), compared with the right kidney of essential hypertension (162 +/- 8, 33 +/- 1). Although effective renal plasma flow rate was not different from normal (191 +/- 8), glomerular filtration rate was significantly higher in the contralateral kidney of RVH than in normal (38 +/- 1). RA was elevated due to the stenotic lesion in the stenotic kidney (28,500 +/- 1,900 dyns.sec.cm-5), while the elevation in the contralateral kidney (10,800 +/- 600) was less than in the right kidney of essential hypertension (14,900 +/- 1,200). RE (5,800 +/- 300) in both kidneys of RVH was higher than in the right kidney of essential hypertension (4,500 +/- 200).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Aspirin test for differentiation of unilateral renovascular hypertension from hyperreninemic essential hypertension.

Responses of renin release and blood pressure to aspirin DL-lysine (ASP) were examined to find out if the responses could help in the differentiation between unilateral renovascular hypertension (RVH) and hyperreninemic essential hypertension (EHT). The two studies involved ten patients with unilateral RVH, eight with hyperreninemic EHT, and five with hyporeninemic EHT. In a radiological study, before and 30 min after an intravenous injection of ASP (18 mg/kg), renal venous and abdominal aortic plasma was sampled and assayed for prostaglandin (PG) E2 and plasma renin activity (PRA). Systemic blood pressure was measured serially. The reproducibility of the responses to ASP was confirmed in a bedside study. In unilateral RVH, ASP suppressed renin release from the stenotic kidney and reduced the renal vein PRA ratio to less than 1.5 via the inhibition of PG synthesis, which is accelerated in that kidney. The mean suppression of aortic PRA at this dose of ASP was 35% in these patients, and their blood pressure decreased in proportion to the suppression of PRA. However, in the two EHT groups, ASP elevated the mean blood pressure. The renal synthesis of PGE2 was inhibited by ASP in all patients, but the suppression of PRA, while small, was significant (19% in the aorta) in the patients with hyperreninemic EHT, and not significant in patients with hyporeninemic EHT. The different responses of blood pressure and PRA to ASP between RVH and EHT were reproducible in the bedside study.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Effects of ouabain and verapamil on endothelin-1-induced contraction of mesenteric artery in young spontaneously hypertensive rats.

We studied the effects of ouabain and verapamil on endothelin-1(ET-1)-induced contraction of the mesenteric artery in prehypertensive spontaneously hypertensive rats (SHRs) and age-matched Wistar-Kyoto (WKY) rats. Rings of mesenteric artery of SHRs and WKY rats aged 4 weeks were superfused with physiological saline solution and isometric tension was measured. ET-1 (10(-9) or 10(-8) M)-induced contractions were significantly larger in WKY rats than in SHRs. ET-1 (10(-7) M)-induced contractions were not significantly different between SHRs and WKY rats. Verapamil markedly inhibited ET-1 (10(-7) M)-induced contractions both in SHRs and in WKY rats. Although the percent inhibition tended to be larger in SHRs than in WKY rats, the difference was not significant. Ouabain significantly increased ET-1 (10(-7) M)-induced contraction in the presence of verapamil both in SHRs and in WKY rats. The increase was significantly greater in SHRs than in WKY rats. As a result, ET-1 (10(-7) M)-induced contractions were significantly greater in SHRs than in WKY rats in the presence of verapamil and ouabain. These results suggest that in ET-1-induced arterial contraction, [Na+]i-mediated [Ca2+]i regulation such as the Na+/Ca2+ exchange system might be greater in SHRs than in WKY rats, and that this might be, at least in part, involved in the pathogenesis or maintenance of hypertension in SHRs.

Animals↗
PubMed1991

Blood pressure responses to intravenous or intracerebroventricular endothelin-1 in spontaneously hypertensive rats.

Responses of blood pressure to intravenous (i.v.) or intracerebroventricular (i.c.v.) endothelin-1 (ET-1) in spontaneously hypertensive rats (SHRs) and Wistar-Kyoto (WKY) rats were investigated. Conscious male SHRs and WKY rats were used for the experiments. ET-1 (300-1,000 ng/kg) was injected intravenously in the i.v. experiments, or 30 and 100 ng/kg of ET-1 were injected into the lateral ventricle in the i.c.v. experiments. The initial depressor response to i.v. ET-1 was greater in SHRs (n = 10) than in WKY rats (n = 10) at 1,000 ng/kg (-54 +/- 6 vs. -41 +/- 3 mm Hg, mean +/- SEM, p less than 0.05). The subsequent pressor response to i.v. ET-1 was smaller in SHRs than in WKY rats (3.5 +/- 0.8 vs. 7.0 +/- 0.9 mm Hg at 300 ng/kg, p less than 0.05, and 11 +/- 2 vs. 17 +/- 2 mm Hg at 1,000 ng/kg, p less than 0.05). Pressor responses to i.c.v. ET-1 were not different in SHRs (n = 8) and WKY rats (n = 8) at both doses (10 +/- 4 vs. 10 +/- 3 mm Hg at 30 ng/kg, and 46 +/- 10 vs. 49 +/- 10 mm Hg at 100 ng/kg). A greater initial depressor response and a smaller subsequent pressor response to i.v. ET-1 were observed in SHRs than in WKY rats. The attenuated pressor response to intravenously administered ET-1 may be unique since vasoconstrictor responses to other known vasoactive substances such as angiotensin, catecholamines, or vasopressin are reportedly augmented in SHRs. We did not find any difference in responsiveness to i.c.v. ET-1 between SHRs and WKY rats.

Animals↗
PubMed1991

Differential effects of endothelin-1 and big endothelin on canine kidneys.

Renal effects of endothelin-1 (ET-1, human, 1-21) and the equivalent molar concentration of big ET (human, 1-38) and the contributions of prostaglandins and endothelium-derived relaxing factor to these actions were examined. Intrarenal infusion of ET-1, at a dose of 0.4 pmol/kg/min, decreased renal blood flow (RBF), glomerular filtration rate (GFR), and urine output (V) to 62, 70, and 45% of control values, respectively. Additional aspirin-DL-lysine (ASP) treatment (25 mg/kg) caused marked decreases in RBF, GFR, and V to 20, 14, and 9% of control values, respectively. During ET-1 infusion, intrarenal infusion of NG-monomethyl-L-arginine (L-NMMA, 1 mumol/min) caused decreases in RBF, GFR, and V. In another group, intrarenal infusion of big ET at a dose equivalent to that of ET-1 did not significantly affect RBF, GFR, or urine output, which were 95, 107, and 84% of control values, respectively. Additional ASP treatment decreased these values to 78, 69, and 52% of control values, respectively. L-NMMA infusion during big ET infusion showed little effect on renal function. Our study demonstrated that intrarenal infusion of ET-1, at a dose of 0.4 pmol/kg/min, caused significant hemodynamic and functional changes in the canine kidney compared with an equivalent molar concentration of big ET.

Animals↗
PubMed1991

Immunoreactive endothelin-1 contents in brain regions from spontaneously hypertensive rats.

To investigate the possible role of brain endothelin-1 (ET-1) in hypertension of spontaneously hypertensive rats (SHRs), we measured immunoreactive (ir) ET-1 contents in brain regions as well as plasma ir-ET-1 levels in SHRs aged 4-5 and 12-14 weeks and age-matched Wistar-Kyoto rats (WKY) with a radioimmunoassay for ET-1. Systolic blood pressures of SHR aged 4-5 and 12-14 weeks were significantly higher than those of corresponding WKY. Significant amounts of ir-ET-1 were detectable throughout the discrete brain regions analyzed in both strains; higher ir-ET-1 contents in structures such as thalamus, hypothalamus, midbrain, pons, medulla, and cerebellum, with the lowest in cerebral cortex, were observed. A reverse-phase high-performance liquid chromatography of the brain extracts revealed the presence of both a major component identical to the elution position of synthetic ET-1 and a minor component possibly corresponding to its oxidized form. When compared, ir-ET-1 contents in all brain regions analyzed were lower in SHRs than in WKY rats. This strain-related change of ir-ET-1 contents was significant in the medulla at 4-5 weeks of age, and in all brain regions except hypothalamus at 12-14 weeks of age. Plasma ir-ET-1 levels, in contrast, were comparable between SHRs and WKY rats. These results suggest that brain ET-1 may be involved in the development and the maintenance of hypertension in SHRs.

Aging↗
PubMed1991

Acute and chronic effects of anti-endothelin-1 antibody on blood pressure in spontaneously hypertensive rats.

To evaluate the significance of endogenous endothelin (ET) in the maintenance of blood pressure in hypertensive and normotensive conditions, we examined the acute and chronic effects of anti-ET-1 antibody in spontaneously hypertensive rats (SHRs) and Wistar-Kyoto (WKY) rats. Immunoglobulin (Ig) solution purified from anti-ET-1 rabbit serum was injected intravenously in conscious rats aged 12-14 weeks (SHR: n = 7, WKY: n = 7). In the control group (SHR: n = 5, WKY: n = 4), Ig prepared from nonimmune rabbit serum was administered. One week after the first injections of Ig, second intravenous injections were given. After the intravenous injections of ET-1 antibody, there were no significant changes in directly measured blood pressure (BP) for up to 60 min in both strains. On the first, third, and seventh days after the first administration of ET-1 antibody, as well as on the first, third, and seventh days after the second injection, there were no appreciable differences in BP between SHR treated with anti-ET-1 antibody and SHR with control Ig. No significant changes in BP were observed throughout the observation period in WKY groups. Plasma levels of immunoreactive ET-1 were similar in SHR and WKY. This study suggests that circulating ET may not play a significant role in the maintenance of hypertension in SHRs or in the regulation of blood pressure in WKY rats.

Animals↗