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Biomedical subjects

Y Sakamoto

Publications and source records attributed to Y Sakamoto.

At least 793 records · Page 44Linked to original sources
PubMed1977

[Effects of somatostatin on pancreatic isolated islets and peripheral tissues of rats].

This study was performed in order to evaluate the effects of somatostatin on insulin releasing mechanisms and on glucose uptake in peripheral tissues using isolated pancreatic islets, isolated rat diaphragms and epididymal fat pads. Insulin release by various concentrations of glucose were examined, and it was found that 100 ng/ml of somatostatin significantly inhibited insulin release at the glucose concentration of 200 mg/dl. Somatostatin also significantly inhibted insulin release by the administration of 5microgram/ml of glucagon with 200 mg/dl of glucose concentration and 20 mM of orginine with 200mg/dl of glucose concentrations. But at the glucose concentration of 50mg/dl, no significant inhibition of somatostatin on insulin release was observed even when various concentrations of glucagon or arginine were added. The influence of somatostatin on peripheral tissues was examined in vitro, and no significant change on glucose uptake compared with the control group was shown in either tissues. The results indicated that somatostatin directly inhibited insulin release from rat pancreatic islets but had no effect on glucose uptake in peripheral tissues. The inhibitory effect of somatostatin on insulin release may act through the common mechanism of both glucose and other substances in leading to insulin release.

Animals↗
PubMed1977

Comparative effects of native insulin and insulin-dextran complexes on the metabolism of adipose tissue.

Insulin-dextran complexes have been prepared and their biological activities compared to that of native insulin. Complexes referred to as T-70 had a molecular weight of about 450 000, T-2000 being more than 2 million. Insulin-dextran T-70 was stable and no release of free insulin from the complex was observed upon its incubation with adipose tissue. Insulin-dextran T-70 mimicked the effects of native insulin upon adipose tissue metabolism. It also lowered blood sugar. These effects necessitated, on an insulin molar basis, concentrations of the complex that were 10-times greater than those needed for native insulin. Maximal concentrations of insulin complex T-70 or native insulin elicited similar quantitative effects. This suggested that when the concentration of insulin-dextran T-70 was high enough, the complex occupied a sufficient number of receptor sites to produce maximal stimulation of the tissue. In contrast, insulin-dextran T-2000 was barely effective, indicating that, probably due to its size, it was unable to reach receptor sites. The size, stability and metabolic effects of insulin-dextran T-70 observed in this study give additional support to the concept that insulin action is probably mediated via a series of events initiated at the level of the plasma membrane of adipocytes.

Adipose Tissue↗
PubMed1977

Demonstration of bidirectional dual A-V nodal pathways in the same patient.

In a patient with documented paroxysmal junctional tachycardia (PJT) electrophysiologic studies were performed using an extrastimulus technique. At an A1-A2 interval of 360 msec, atrial extrastimulus revealed sudden prolongation of an A2-H2 interval from 370 to 540 msec and PJT ensued. This finding was consistent with antegrade dual A-V nodal pathways. On the other hand, at a V1-V2 interval of 540 msec, ventricular estrastimulus showed a jump in ventriculo-atrial (V-A) conduction time with evidence of delay in the A-V node from 285 to 565 msec and a ventricular echo followed. This finding was consistent with retrograde dual A-V nodal pathways. Mechanisms of bidirectional dual A-V nodal pathways are discussed.

Aged↗
PubMed1977

Effects of sodium, potassium and calcium ions on the slow wave in the circular muscle of the guinea-pig stomach.

1. The contribution of Na, K and Ca ions to the generation of slow waves in the circular muscle of the guinea-pig stomach was studied.2. The slow waves had a lower, potential-independent (first) and an upper, potential-dependent (second) component. Reduction of the external Na prolonged the first component, but complete removal of Na depolarized the membrane and caused deterioration of the slow wave.3. Readmission of Na (5-10 mM) restored the slow wave; this action was not abolished by ouabain.4. Removal of K depolarized the membrane and slightly reduced the amplitude and duration of the slow waves. Readmission of K hyperpolarized the membrane and increased the amplitude and duration of the slow waves, particularly of the first component. Ouabain blocked the effects on the membrane potential, but not the effects on the slow waves.5. An increase in extracellular Ca prolonged the first component and reduced the frequency. Removal of extracellular Ca abolished the slow wave activity. Excess Ca enhanced, and low Ca reduced the effects of altering the concentrations of external K.6. It is concluded that the ouabain-sensitive Na-K pump may not be directly involved in generating slow waves, but that some other metabolic process is involved, which is regulated to a large extent by Ca, and possibly also by Na and K.

Animals↗
PubMed1977

A comparative study of the effects of OPC-1085 and propranolol on isolated guinea pig atrium.

Effects of a newly synthesized beta-blocker, 5-(3-tert-butylamino-2-hydroxy) propoxy-3,4-dihydrocarbostyril (OPC-1085) were compared with those of propranolol. OPC-1085 had a potency about 3 times greater than that of propranolol in blocking the positive inotropic and chronotropic effects of isoprenaline on the isolated guinea pig atrium. At a concentration of over 3 X 10(-5) M OPC-1085 produced negative inotropic and chronotropic effects. However, these effects were about 10 times weaker than those of propranolol. Suppressing effects on the rate of rise and on the maximum driving frequency of action potentials were also more than 10 times less than those of propranolol. There was almost no change in the action potential of vagus nerve after a 10 min treatment with OPC-1085 (10(-5) M), while the action potential was reduced to 60-70% with propranolol (10(-5) M).

Action Potentials↗
PubMed1977

Paroxysmal supraventricular tachycardia with unusual induction. Concealed reentry or automaticity?

In a patient with documented paroxysmal supraventricular tachycardia, earlier atrial extrastimuli consistently induced His-ventricle (H-V) block and "atrioventricular junctional" beats, which were always followed by an echo or paroxysmal supraventricular tachycardia. In "atrioventricular junctional" beats, a V wave was preceded by an H deflection with the same intervals as that of the sinus beat. As for the underlying mechanism of paroxysmal supraventricular tachycardia, two possibilities were considered: (1) concealed atrioventricular nodal reentry, and (2) "triggered automaticity."

Adult↗
PubMed1977

Demonstration of two anomalous bypasses in concealed Wolff-Parkinson-White syndrome.

Two patients with a history of paroxysmal supraventricular tachycardia but no evidence of the Wolff-Parkinson-White syndrome in the conventional electrocardiograms were studied utilizing atrial and ventricular extrastimuli. The evidence obtained in these patients was consistent with a concealed Wolff-Parkinson-White syndrome. In one patient, ventricular extrastimuli revealed three different responses in the curve of ventriculoatrial conduction, depending upon the interval of stimulus. In the other patient, intracardiac recordings, including the left atrial potential, showed that paroxysmal supraventricular tachycardia was induced by an impulse via an anomalous bypass which diverged from the main bypass or stemmed independently from the left ventricle and was maintained by impulses via the main bypass which lay between the left ventricle and the left atrium. The mechanisms for initiation of the paroxysmal supraventricular tachycardia were discussed.

Adult↗