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Biomedical subjects

T Okamura

Publications and source records attributed to T Okamura.

At least 325 records · Page 18Linked to original sources
PubMed1995

Functional role and histological demonstration of nitric-oxide-mediated inhibitory nerves in dog sphincter of Oddi.

Nitric oxide (NO) plays an important physiological role in regulating gastrointestinal motility. Involvement of endogenous NO was evaluated in the response to non-adrenergic, non-cholinergic (NANC) nerve stimulation of the dog sphincter muscle of Oddi. Transmural electrical stimulation (TES), nicotine (10(-5) M) and K+ (10 mM) produced only a relaxation in the sphincter muscle strips contracted with substance P, which was not potentiated by atropine. The TES-induced relaxation was abolished by tetrodotoxin (3 x 10(-7) M) and oxyhaemoglobin (1.6 x 10(-5) M), but not affected by atropine (10(-7) M), propranolol (10(-7) M), phentolamine (10(-7) M), indomethacin (10(-6) M), cholecystokinin (CCK, 10(-8) M) and vasoactive intestinal polypeptide (VIP, 10(-8) M). The relaxation was also abolished by treatment with NG-nitro-L-arginine (L-NA, 10(-5) M), an NO synthase inhibitor. Nicotine produced a transient relaxation, which was abolished by tetrodotoxin, hexamethonium (10(-5) M) and L-NA, but not affected by atropine and NG-nitro-D-arginine (D-NA, 10(-5) M). The addition of K+ elicited a transient relaxation, which was abolished by tetrodotoxin and L-NA. The inhibitory effects of L-NA were antagonized by L-arginine (10(-3) M). The presence of neurons containing nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase was histochemically demonstrated in the sphincter of Oddi. These findings may indicate that TES, nicotine and K+ liberate NO from NANC inhibitory nerve which is involved in the relaxation of the dog sphincter of Oddi. The muscular tone does not seem to be regulated by cholinergic nerves under the experimental conditions used.

Analysis of Variance↗
PubMed1995

Characteristics of DQ2511-induced relaxation in isolated dog, monkey and human arteries.

DQ2511, a possible antiulcer agent, relaxed dog, monkey and human arterial strips from various organs; the effect was most evident in the gastroepiploic artery. The relaxation was not influenced by timolol, atropine, dopamine receptor antagonists, and K+-channel blockers, but partially attenuated by oxyhemoglobin endothelium denudation. Treatment with DQ2511 increased the relaxant response to sodium nitroprusside and a prostaglandin I2 analog in dog gastroepiploic arteries and potentiated the stimulating effect of these agonists on the contents of cyclic GMP and cyclic AMP, respectively. It is concluded that DQ2511 relaxes gastroepiploic arteries predominantly over the other arteries; the relaxation appears to be derived partially from phosphodiesterase inhibition.

Animals↗
PubMed1995

Detection and monitoring of simple renal cysts with computed tomography.

We retrospectively investigated the incidence of simple renal cysts in 1,288 healthy subjects, and monitored the growth and formation of such cysts in 39 subjects using abdominal computed tomography (CT). Simple renal cysts were detected in 138 (10.7%) of the 1,288 subjects. The incidence of simple renal cysts increased significantly with the subject's age (p < 0.001). We found that cyst size increased significantly with age and over time on serial CT studies (p < 0.001). Exoparenchymal cysts, comprising greater than 50% of extraparenchymal lesions, were significantly larger than endoparenchymal cysts (p < 0.001), and showed a greater tendency to increase in size over time.

Adolescent↗
PubMed1995

Nitroxidergic innervation in dog and monkey renal arteries.

We analyzed mechanisms underlying neurogenic vasodilatation in dog and Japanese monkey renal arteries. Isometric mechanical responses of the arterial strip to nerve stimulation by nicotine were recorded. Nicotine-induced contractions were abolished by hexamethonium and potentiated by NG-nitro-L-arginine, a nitric oxide synthase inhibitor. The potentiating effect was reversed by L-arginine. NG-Nitro-L-arginine did not potentiate the contraction caused by norepinephrine. The nicotine-induced contraction was reversed to a relaxation by prazosin. The relaxation was not influenced by indomethacin, timolol, or atropine but was abolished by NG-nitro-L-arginine, methylene blue (a guanylate cyclase inhibitor), oxyhemoglobin (a nitric oxide scavenger), and hexamethonium. In the strips treated with NG-nitro-L-arginine, the nicotine-induced relaxation was restored by L-arginine. Histochemical study demonstrated perivascular nerves containing NADPH diaphorase and nitric oxide synthase immunoreactivity in dog and monkey arteries. We conclude that renal arteries are innervated by nitric oxide-mediated vasodilator and adrenergic vasoconstrictor nerves, and depression of the vasodilator nerve function by nitric oxide synthase inhibition potentiates the contraction caused by adrenergic nerve excitation.

Animals↗
PubMed1995

Splitting of high right atrial potentials in atrial flutter with rapid pacing.

Rapid pacing from the high right atrium was performed in 7 patients with atrial flutter in whom potentials with multicomponent high-frequency deflections were recorded at the high right atrium to examine the origin of these potentials during transient entrainment in atrial flutter. In all of the patients with relatively slow rapid pacing, the potentials were captured orthodromically through the atrial flutter reentry circuit with a long conduction time. With more rapid pacing, the potentials were split into 2 associated components: P1 and P2. P1 was captured antidromically with a short conduction time whereas P2 was captured persistently in an orthodromic direction through the reentry circuit with a progressively long conduction time. In 3 of the 7 patients, atrial flutter was converted into another atrial flutter by rapid pacing. During this other atrial flutter, the potentials at the high right atrium were split from the beginning to form double potentials: D1 and D2. During rapid pacing, D1 and D2 were fused, and D1 was captured antidromically whereas D2 was captured orthodromically through the reentry circuit. In sinus rhythm, the potentials at the high right atrium formed fractionated potentials. These findings suggest that 1) fractionated potentials may represent 2 atrial regions with different conductivity properties, 2) fractionated potentials may be able to change into double potentials, and 3) double potentials may be attributable to their conductivity properties rather than refractoriness.

Action Potentials↗
PubMed1995

[Effect of the novel calcium antagonist AE0047 on responses of isolated dog blood vessels to vasoconstricting agents and to nerve stimulation].

The effect of AE0047 on contractile responses to high K+ and agonists and to perivascular nerve stimulation was investigated using isolated dog cerebral, coronary and mesenteric arteries and mesenteric veins. AE0047 inhibited concentration-dependent contractions induced by KCl, norepinephrine, prostaglandin (PG) F2 alpha and serotonin. The inhibition of contractions caused by PGF2 alpha and serotonin was greater in cerebral arteries than in mesenteric arteries. The inhibitory effect of AE0047 on norepinephrine-induced mesenteric arterial contraction persisted for 24 hr or longer even though the strips were repeatedly washed. Greater inhibition was obtained in the arteries contracted with K+ than in those contracted with agonists. AE0047 reduced Ca(2+)-induced contraction in K(+)-depolarized mesenteric artery strips to a greater extent than those in PGF2 alpha-stimulated strips. The relaxation induced by transmural electrical stimulation in coronary arteries treated with phenotolamine was reduced by AE0047, whereas the norepinephrine-induced relaxation was unaffected. In cerebral arteries treated with superoxide dismutase, AE0047 reduced nicotine-induced relaxation but not NO-induced relaxation. These findings suggest that AE0047 selectively inhibits vasocontractions via voltage-dependent Ca channels and preferentially inhibits cerebroarterial contraction, these actions being long-lasting. AE0047 appears to reduce the release of neurotransmitter from adrenergic and nitroxidergic nerve terminals in blood vessels.

Animals↗
PubMed1995

Nitric oxide-mediated neurogenic relaxation in monkey mesenteric veins.

The purpose of this investigation was to determine if neurally induced vasodilatation is mediated by nitric oxide (NO) in monkey mesenteric veins. Helical strips of the monkey mesenteric vein were exposed to the bathing media for isometric tension recording, and perivascular nerves were stimulated by nicotine. Nicotine produced a contraction, which was potentiated by treatment with NG-nitro-L-arginine, a NO synthase inhibitor, the effect being reversed by L-arginine. The nicotine-induced contraction was reversed to a relaxation by prazosin. The relaxation was abolished by the NO synthase inhibitor, and it was restored by L-arginine. D-Enantiomers were without effect. The response was not influenced by timolol and indomethacin, but was abolished by hexamethonium and oxyhemoglobin. There were perivascular nerve fibers containing NO synthase immunoreactivity in the monkey vein. Neurally induced venous relaxations appear to be mediated by NO from perivascular nerves, as seen in dog and monkey mesenteric arteries. It is concluded that monkey mesenteric veins are innervated by nitroxidergic and adrenergic nerves, which may balance the vascular tone.

Animals↗
PubMed1995

Comparison of the effect of dopamine in primate arteries and veins.

Mechanical responses to dopamine of isolated human and monkey veins were isometrically measured and compared to those of the arteries. Human gastroepiploic and monkey mesenteric veins responded to dopamine with contractions, whereas the arteries in the same region responded with relaxations. Treatment with phentolamine converted the venous contraction to a relaxation, which was not influenced by propranolol but was abolished by droperidol. The relaxation was endothelium-independent and converted to a contraction by SCH23390 but unaltered by domperidone. Dopamine increased the cyclic AMP content in the human veins. Monkey vena cava and portal vein did not respond to dopamine with relaxation even under alpha-adrenoceptor blockade. It is concluded that primate veins and arteries from the gastric and mesenteric regions respond quite differently to dopamine; the alpha-adrenoceptor-mediated contraction predominates over the relaxation mediated via D1-receptor in the veins, and vice versa in the arteries. In monkey large veins, dopamine receptor does not appear to play a functional role. The veno-constrictor action of dopamine, together with actions on myocardium and resistance vessels, would contribute to increasing of the cardiac output.

Animals↗
PubMed1995

Polysplenia syndrome with common atrioventricular canal and persistent truncus arteriosus.

A case of an infant with a rare combination of polysplenia syndrome with common atrioventricular canal and persistent truncus arteriosus is presented. In our present case, severe common atrioventricular valve regurgitation was identified, as in previous cases. To our knowledge, echocardiographic and autopsy findings of this association has not been previously reported. The persistent truncus arteriosus is extremely rare in the setting of the polysplenia syndrome, but the present case report demonstrates that these anomalies may, at times, occur.

Abnormalities, Multiple↗
PubMed1995

Pulmonary embolism after cerebral angiography--three case reports.

Three patients developed acute pulmonary embolism after cerebral angiography. The diagnoses were based on the clinical symptoms and echocardiography, chest roentgenography, blood gas analysis, and pulmonary perfusion scans after intravenous injection of 5 mCi of technetium-99m-labeled human albumin macroaggregates. Two of the three patients achieved clinical improvement, but one patient with severe embolization and circulatory deterioration died in spite of anticoagulation therapy. Recognition of the potential risk of pulmonary embolism after angiography and active prophylaxis are most important in preventing this complication.

Adult↗
PubMed1995

Cerebral sparganosis mansoni--case report.

An 80-year-old male with paresis of the right upper extremity underwent surgery for a suspected metastatic brain tumor. A live Sparganum mansoni worm was removed from the parietal lobe through a left parietal craniotomy. Retrospective evaluation of magnetic resonance (MR) images revealed ipsilateral ventricular dilatation, despite the presence of a mass lesion resembling a metastatic brain tumor. This interesting MR imaging finding is an important point for differentiating between a brain tumor and cerebral sparganosis.

Aged↗
PubMed1995

[Radiological diagnosis of renal oncocytoma].

Eight patients (nine tumors) with histologically proven renal oncocytoma are presented. In all cases, differential diagnosis between renal oncocytoma and renal cell carcinoma could not be done on ultrasonography. On selective renal angiography, extended arteries surrounding the tumor margin was demonstrated in six of seven tumors without a spoke-wheel arterial supply. A sharp and smooth margin with capsule (lucent rim) could be found in five cases, and a spoke-wheel configuration of vessels could be seen in only two cases. A spoke-wheel pattern might be found with tumor growth. All tumors on computed tomography (CT scan) have a distinct margin, a smooth contour and a homogeneous appearance on contrast enhanced CT scan. The capsule and the presence of a central scar were clearly seen on T1 and T2 weighted images of magnetic resonance imaging (MRI). It is helpful to differentiate the oncocytoma from renal cell carcinoma. The modality of MRI may be useful in the preoperative diagnosis of oncocytoma.

Adenoma, Oxyphilic↗
PubMed1995

Mechanisms underlying endothelium-independent relaxation by acetylcholine in canine retinal and cerebral arteries.

Canine retinal central arterial strips responded to acetylcholine with a relaxation that was endothelium-independent. Indomethacin and atropine abolished the relaxation at low doses (10(-7) to 10(-6) M) and moderately attenuated the response to high concentrations (10(-5) and 10(-4) M). The residual relaxation at 10(-5) and 10(-4) M in indomethacin-treated strips were abolished by NG-nitro-L-arginine, hexamethonium, oxyhemoglobin and methylene blue, and the NG-nitro-L-arginine-induced inhibition was reversed by L-arginine. Cerebral arterial strips with endothelium responded to acetylcholine with a transient relaxation followed by a contraction, whereas only a relaxation was induced when endothelium was denuded. The relaxations at low and high doses were modified by atropine, indomethacin, hexamethonium and NG-nitro-L-arginine quite similarly to those seen in retinal arteries. Histochemical study demonstrated the presence of perivascular nerves containing NADPH diaphorase in whole mount preparations of the retinal artery. It is concluded that acetylcholine-induced retinal arterial relaxations, independent of endothelium, are mediated possibly by prostaglandin I2 in activation of muscarinic receptors and by nitric oxide derived from perivascular nerves in response to nicotinic receptor stimulation. On the other hand, vasoconstrictor prostanoids appear to be liberated from the endothelium by muscarinic receptor stimulation in cerebral arteries, and mechanisms underlying the relaxation are similar to those seen in retinal arteries.

Acetylcholine↗
PubMed1995

Comparison of bone scans, parathyroid hormone levels and bone mineral densities in hemodialysis patients.

We have evaluated bone scans, parathyroid hormone (PTH) levels and bone mineral densities (BMDs) of hemodialysis (HD) patients. The bone scans were grouped into 4 types (type 1-4). Type 1 showed a diffusely high activity of the tracer in the whole skeleton especially in the skull: secondary hyperparathyroidism pattern. Type 2 showed high background activity, the same pattern as osteomalacia. Type 3 was a mixture of types 1 and 2. Type 4 was almost normal. The PTH levels of type 1 were higher and the radius BMDs were lower than those of the other types. The radius BMDs in one third of type-2 patients were lower than the normal range. A comparison of bone scans, PTH and BMDs helps to evaluate bone changes in HD patients.

Adult↗
PubMed1995

[A case of peritoneal metastasis from retroperitoneal yolk sac tumor diagnosed by 67Ga-scan and 18F-FDG-PET].

Yolk sac tumor is one of the histological types of germ cell tumors. Primary retroperitoneal germ cell tumors are extremely rare neoplasms. We report a case of peritoneal metastasis after resection of a primary retroperitoneal germ cell tumor. The peritoneal metastases were detected by 67Ga-scan when CT did not suggest metastatic lesions while the level of alphafetoprotein was still elevated. The 67Ga-scan showed multiple hot spots in the abdomen and pelvis 72 hours after intravenous injection of the tracer and no changes were observed in serial scan taken 6 hours after the first scan. These findings were strongly suggested the dissemination of the malignant tumors. A PET study with 18F-fluorodeoxyglucose was performed and showed extensive uptake in the intraabdominal and intrapelvic cavity. It was also useful for understanding the extension and distribution of the peritoneal metastatic lesions. The sites of the accumulation of 18F-fluorodeoxyglucose corresponded to the results found in postmortem.

Adult↗
PubMed1995

[Assessment of bone mineralization of hemodialyzed patients with SPA and DPA--different effect of PTX with the site].

We analyzed the bone changes at each site of secondary hyperparathyroidism (2 degrees HPT) on hemodialyzed patients using both single photon absorptiometry (SPA) and dual photon absorptiometry (DPA). The subjects were 35 hemodialysis patients (12 male, 24 female) with 2 degrees HPT. The bone mineral densities (BMD) of 1/3 radius, head, total body and 3rd lumbar spine were measured before and after parathyroidectomy (PTX). Before PTX, the BMD of 2 degrees HPT patients were lower than the normal range of all sites, especially at the radius which mainly consisted of cortical bone. After PTX, the BMD at all sites increased especially in the head. The BMD of the radius also continued to increased up two years after PTX, but it was not as increased as the BMD of head. The BMD of the lumbar spine which consisted of cancellous bone mainly increased after PTX for one year and decreased thereafter. This decrease was influenced by age. There was a difference with the site of BMD after PTX. The determination of changes of BMD of head and radius was considered useful for the judgment of treatment.

Absorptiometry, Photon↗