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Biomedical subjects

E Nishimura

Publications and source records attributed to E Nishimura.

47 records · Page 3Linked to original sources
PubMed1984

Contractile effects of cysteamine on the guinea-pig ileum.

Cysteamine (beta-mercaptoethylamine HCl) (1.0-40.0 mM) induced a concentration-dependent increase in tonic and phasic contractions of segments of guinea-pig ileum in vitro. Myenteric plexus-longitudinal muscle (MPLM) preparations also responded with an increase in tonic contractions but phasic contractions were either greatly reduced or absent, indicating that these were a response of the circular muscle. Atropine (5 microM) inhibited the cysteamine-induced contractions, whereas hexamethonium and guanethidine had no effect, suggesting that cysteamine was acting at least partly via a cholinergic mechanism involving muscarinic receptors. Tetrodotoxin increased the phasic contractions of ileal segments, but had no effect on the tonic component. Treatment of MPLM preparations with morphine (1 microM) resulted in a small reduction in responsiveness to cysteamine, and blocked electrically-induced contractions by at least 90%. Since morphine acts by inhibiting acetylcholine release via hyperpolarization of intrinsic neurones, a small but significant part of the cysteamine-induced contractions probably resulted from stimulation of acetylcholine release from intrinsic neurones. Following a response to high cysteamine concentrations (greater than 15 mM) tissues were refractory to subsequent cysteamine administration. Cross-desensitization between cysteamine and acetylcholine also occurred, as short-term (1-3 min) incubation of MPLM preparations with high concentrations of either compound (1-10 microM acetylcholine or 20 mM cysteamine) resulted in a reduced responsiveness to both. A reduced sensitivity to acetylcholine or cysteamine was obtained following long-term (45 min) incubation with acetylcholine (1 microM). Removal of Na+ from the incubation medium negated this effect. In contrast, the refractoriness to acetylcholine or cysteamine following long-term (45 min) incubation with cysteamine (20 mM) was accentuated in low Na+ medium. It is suggested that cysteamine induces a contraction of both the circular and longitudinal muscle of the guinea-pig ileum by stimulating the release of acetylcholine from intrinsic neurones, by an action at the level of the smooth muscle muscarinic receptor, and possibly by a non-cholinergic mechanism. However, the mechanisms by which acetylcholine and cysteamine induce tissue refractoriness probably differ.

Animals↗
PubMed1984

Effect of cysteamine on secretion of gastrin and somatostatin from the rat stomach.

Cysteamine (beta-mercaptoethylamine HCl) administration to rats induces a hypergastrinemia and a reduction in gastric tissue somatostatin content. The possibility that this reduction may contribute to the elevated gastrin levels has been investigated in the isolated perfused rat stomach. Cysteamine (1 mM) rapidly increased immunoreactive gastrin release to levels ranging between 41% and 125% above basal. Increasing the dose to 10 mM caused a 1148% increase in immunoreactive gastrin. Secretion of somatostatinlike immunoreactivity did not change. Perfusion of gastric inhibitory polypeptide (1 nM) induced a sustained increase in somatostatinlike immunoreactivity secretion and a transient rise in gastrin. Addition of 10 mM cysteamine during gastric inhibitory polypeptide perfusion caused a 300% increase in immunoreactive gastrin. These levels were lower than in response to cysteamine alone. The results demonstrate that cysteamine can stimulate immunoreactive gastrin secretion without any change in somatostatinlike immunoreactivity release. When somatostatinlike immunoreactivity secretion is stimulated by an agent such as gastric inhibitory polypeptide, the cysteamine-induced release of immunoreactive gastrin is attenuated, suggesting the presence of a functional linkage between somatostatin and gastrin under these conditions.

Animals↗
PubMed1983

Enkephalinergic control of somatostatin secretion from the perfused rat stomach.

A role for the enkephalins in the regulation of gastric somatostatin (SLI) secretion has been investigated in an isolated perfused rat stomach model. Both methionine- and leucine-enkephalins caused a dose-dependent inhibition of gastric inhibitory polypeptide (GIP) stimulated SLI secretion. Leu-enkephalin was one order of magnitude less potent than met-enkephalin: 50% inhibition by met-enkephalin was at 4 X 10(-9) M and with leu-enkephalin 3.5 X 10(-8) M. Naloxone (100 nM) had no effect on basal secretion but blocked the inhibitory action of met-enkephalin (1 nM or 1 microM). Vagal stimulation (7 V, 10 Hz, 5 ms) inhibited GIP-stimulated SLI release. Administration of naloxone partially reversed this inhibition, suggesting that endogenous opioids were at least partially responsible for vagally induced inhibition. A number of possible pathways by which endogenous enkephalins may modulate SLI release have been proposed.

Animals↗
PubMed1980

Insulin permeability of hydrophilic polyacrylate membranes.

The diffusive permeability of insulin in polyhydroxyethyl methacrylate (37.1% water), polyhydroxyethyl acrylate (51.8% water), polymethacrylic acid (67.5% water), and cuprophane PT-150 membranes was determined and correlated with the weight fraction of water in the membrane. Insulin diffusivity in the membranes was determined to be 1.0 x 10(-6) cm2/sec, which is in reasonable agreement with literature values for insulin diffusivity in water.

Acrylates↗
PubMed1979

Effects of intraaortic balloon counterpulsation on regional myocardial function during acute coronary occlusion in the dog.

The effects of intraaortic counterpulsation on regional myocardial function were studied using ultrasonic dimension gauges in 24 open chest dogs. Pairs of ultrasonic crystals were implanted in the subendocardium of the left ventricle in control, marginally ischemic and ischemic segments. After coronary arterial occlusion, the end-diastolic length of all three segments was increased. Segment shortening was rapidly replaced by systolic expansion in the ischemic segment. In the marginal segment, active shortening decreased by 53% and, in the control segment, shortening was augmented by compensatory operation of the Frank-Starling mechanism. Balloon pumping initiated 10 minutes after coronary occlusion resulted in an increase in mean aortic diastolic pressure from 103 to 115 mm Hg without any significant change in peak systolic pressure. In the marginal segment, end-diastolic length decreased by 3%, and previously reduced shortening increased to 82% of control value, deteriorating again with discontinuation of counterpulsation. Balloon pumping produced no change in the dyskinetic motion of the ischemic segment but caused compensatory augmentation of shortening of the control segment. Thus, counterpulsation selectively improved segment function of the marginally ischemic segment, presumably as a result of a regional increase in myocardial blood flow and in availability of oxygen due to augmented perfusion pressure. The systolic unloading effect was counterbalanced by improved cardiac performance.

Acute Disease↗
PubMed1979

Dynamic geometry of the left atrium and left ventricle in acute mitral regurgitation.

The instantaneous transverse diameter of the left atrium, left ventricular free wall segment length (SEG), and the long axis of the anterior papillary muscle (APM) length were measured throughout the cardiac cycle, using ultrasonic dimension gauges together with left atrial and left ventricular pressures in 12 open-chest dogs. During atrial contraction, left atrial diameter decreased from 19.7 to 18.7 mm, while left ventricular dimensions increased simultaneously. During ventricular ejection, percent shortening was 26% in SEG and 10% in APM, while atrial diameter increased continuously to 20.5 mm, with a concomitant rise in the v wave of left atrial pressure. After normal mitral valve opening, left atrial diameter decreased rapidly simultaneously with the y descent of atrial pressure. Graded mitral regurgitation was then produced by sectioning the chordae tendineae. With moderate mitral regurgitation, end-diastolic length of the SEG increased by 27%, while extent of shortening (delta L) was augmented by 96%. End-diastolic length of the APM increased by 7%, and delta L was augmented by 60%. Left atrial pressure was sharply elevated, with a distinct a wave followed by the more prominent v wave. End-diastolic diameter of the left atrium was enlarged to 22.9 mm with increased atrial shortening and expansion. As mitral regurgitation was increased to a severe degree by additional chordal rupture, end-diastolic length and delta L continued to increase both in SEG and APM. Left atrial pressure was further elevated (a wave 25 mm Hg and v wave 47 mm Hg). Left atrial end-diastolic diameter further increased in 24.9 mm. However, the amplitude of left atrial shortening and expansion decreased remarkably. In severe mitral regurgitation, isoproterenol and nitroprusside decreased left atrial pressure and diameter, restoring more forceful atrial shortening.

Acute Disease↗
PubMedDate not supplied

A porcine model of chronic peripheral arterial occlusion.

PURPOSE: To create a simple and reproducible model of chromic thrombosis for the evaluation of thrombolytic agents and devices. MATERIALS AND METHODS: A stenosis was created in the superficial femoral artery of domestic swine, and autologous blood clot was deposited above the stenosis. Follow-up last for up to 3 months. Degree of clot organization was determined at histologic examination. Two thrombolytic agents, urokinase and collagenase, were used to test this model. RESULTS: There was a 27% delayed recanalization rate with this model. At histologic examination, early thrombus organization was seen at the vessel periphery after 10 days. One-month-old thrombus was substantial but variable in amount. Three-month-old thrombus was completely organized. Neither urokinase nor collagenase proved effective against chronic clot in the doses and time course of this study. CONCLUSION: This simple method yields a chronic porcine clot in a reliable number of domestic swine in 1 month.

Animals↗
PubMedDate not supplied

Percutaneous creation of acute type-B aortic dissection: an experimental model for endoluminal therapy.

PURPOSE: To evaluate the feasibility of a percutaneously created type-B aortic dissection as an experimental model for percutaneous therapy. This model was used to evaluate the hemodynamic effects of single-balloon fenestration of the intimal flap. MATERIALS AND METHODS: Acute type-B dissections were created in descending aortae of 15 swine via a femoral (n = 6) or carotid (n = 9) approach. The initial subintimal tear was made with use of a Colapinto needle. The dissections were extended to a predefined position in the aorta. The proximal and distal tears were balloon dilated. The mural flap was balloon fenestrated in six animals, just above the celiac artery. Aortograms were obtained to establish the presence and extent of the dissection. Manometry was performed in both lumina to evaluate the hemodynamics of the dissected aorta and the effects of balloon fenestration in this model. Pathologic specimens were also examined. RESULTS: Creation of dissection was successful in 11 of 15 animals, with six developing true lumen narrowing (group A). The other five animals (group B) had flow in both lumina without evidence of true lumen narrowing. After the creation of a single-balloon fenestration in the group A swine, the arteriograms revealed no evidence of blood admixture between the true and false lumina, and there was no change in the intravascular pressures. Examination of the explanted aortae showed a more extensive circumferential dissection in group A animals as compared with group B. CONCLUSION: The percutaneously created acute type-B aortic dissection is a feasible model for experimentation. The hemodynamics of the aorta did not change after single-balloon fenestration in this model.

Aortic Dissection↗
PubMedDate not supplied

Evaluation of right-ventricular function by Doppler echocardiography in patients with chronic respiratory failure.

In patients with chronic respiratory failure, right-ventricular function was non-invasively evaluated by Doppler echocardiography. A total of 31 patients (16 men, 15 women; mean age 65.8 +/- 7.12 years) with pulmonary tuberculosis sequelae who had received home oxygen therapy during the preceding 6 or more months, were studied. Right-ventricular inflow and outflow waveforms were recorded, and right-ventricular function was evaluated using a new Doppler index combining systolic and diastolic function. On continuous wave Doppler echocardiography, estimated systolic pulmonary arterial pressure was calculated from the gradient between the right atrium and right ventricle. There was no correlation between the new Doppler index and systolic pulmonary arterial pressure, and some patients showed high index values despite low systolic pulmonary arterial pressure. The new Doppler index facilitated evaluation of ventricular function irrespective of right-ventricular afterload.

Aged↗