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Biomedical subjects

W Tan

Publications and source records attributed to W Tan.

At least 127 records · Page 7Linked to original sources
PubMed1991

Effect of manganese (II) bis(glycinate)dichloride on Ca2+ channel function in cultured chick atrial cells.

Manganese (II) bis(glycinate)dichloride (Mn(glycinate)2) is a coordination complex of manganese with application as a contrast enhancement agent for magnetic resonance imaging in the heart. To determine the cardioactivity of the manganese ion in this chelation cage, the effects of Mn(glycinate)2 on Ca channel function in the cultured chick atrial cell was studied. Mn(glycinate)2 decreased amplitude of contraction in chick atrial cells from embryos 14 days in ovo with complete inhibition of beating at 1 mM and half-maximal effect at 0.1 mM. Under control conditions, Bay K 8644, a Ca channel activator increased amplitude of contraction by 86% with a half maximal effect at 3.2 x 10(-7) M. In the presence of 0.025 mM Mn(glycinate)2, a concentration which had no effect on the amplitude of contraction, the maximum response to Bay K 8644 was decreased to 31%. Mn(glycinate)2 had no effect on the EC50 for the response to Bay K 8644, 1.7 +/- 0.1 x 10(-9) M (S.E.M., n = 4) in control cells compared to 2.2 +/- 0.4 x 10(-9) M (S.E.M., n = 4) in cells incubated with Mn(glycinate)2. 45Ca2+ uptake over 5 min in cultured chick atrial cells decreased from 2.0 nmol/mg protein in control cells to 1.5 nmol/mg protein in the presence of 10(-5) M PN200-110, a Ca2+ channel blocker, a decrease of 28%. 45Ca2+ uptake decreased to 0.94 nmol/mg protein (53%) in the presence of 1 nmol Mn(glycinate)2. Effects of Mn(glycinate)2 and PN200 were not additive. These data demonstrate that Mn(glycinate)2 exerts its negative inotropic effect, at least partially, by interfering with the function of the L-type Ca channels at high concentrations.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1991

[Determination of circulating antigen in cysticercosis patients using McAb-based ELISA].

For the first time, the determination of circulating antigen in patients with cysticercosis using specific monoclonal antibody against cysticercus antigen (CCyl) based on inhibitive ELISA was reported. The circulating antigens were detected in the sera from 83 patients with cysticercosis, the positive rate being 71.1%. The range of the detectable serum antigen concentrations was 0.16-128 micrograms/ml. In 41 cases of cysticercosis patients, circulating antigens were determined in both sera and cerebrospinal fluids, the positive rates being 68.3% and 78% respectively, the total positive rate being 90.2%. In 114 sera from normal persons, circulating antigen was absent. In 30 sera from patients with hydatidosis, 30 with clonorchiasis, 20 with schistosomiasis japonica, 24 with paragonimiasis, and 5 sera collected from non-parasitosis patients, serum circulating antigen was not detectable. In another 10 non-parasitosis patients, circulating antigen was not found in cerebrospinal fluid. After chemotherapy for one half to one year, in 21 out of 23 cases of cysticercosis patients, the circulating antigen levels in sera dropped to zero, except for two cases having an antigen level of 0.64 micrograms/ml and 1.6 micrograms/ml, respectively. Our results showed that the determination of the circulating cysticercus antigen was very specific for the diagnosis of active infection of cysticercosis and could be used as a rational tool in monitoring the effectiveness of chemotherapy.

Animals↗
PubMed1989

Acute carotid baroreflex resetting in conscious dogs.

1. Acute baroreflex resetting in the control of arterial pressure was studied in six chronically instrumented, conscious dogs. Following aortic baroreceptor denervation, the carotid sinuses were surgically prepared for reversible vascular isolation. 2. During the experiments both carotid sinuses were temporarily isolated from the systemic circulation and conditioned with a pulsatile pressure. The carotid sinus conditioning pressure (CPCSP) was at a level of 100, 140 or 60 mmHg for 20 min each. Carotid sinus pressure (CSP) versus mean arterial pressure (MAP) baroreflex curves were constructed after each conditioning period. 3. The baroreflex curves were shifted downward and to the left at low CPCSP and upward and to the right at high CPCSP. 4. We used four parameters to quantify baroreflex resetting. These were: (1) the set point pressure (PSP), (2) the threshold pressure (PTh), (3) BP50 or mid-point pressure and (4) the CSP at maximum gain (PGmax). At high CPCSP, these four parameters were increased by 18.5 +/- 4.0, 23.4 +/- 4.3, 21.7 +/- 5.0 and 22.0 +/- 5.1 mmHg, respectively (P less than 0.05). 5. Resetting was not complete in these studies. The extent of resetting was approximately 50% for upward and 35% for downward baroreflex conditioning. 6. Analysis of the present experimental data indicates that when the cardiovascular system is exposed to a short-term hyper- or hypotension, the baroreflex is capable of correcting the baseline arterial pressure while preserving its ability to buffer transient disturbances as a result of partial resetting.

Animals↗
PubMed1989

PGE2 and arachidonate inhibit the baroreflex in conscious dogs via cardiac receptors.

Prostaglandin (PG) I2 and PGE2 are known to stimulate left ventricular receptors with nonmyelinated vagal afferents. The present experiments were performed to determine the effects of intracoronary infusion of PGE2 (10-50 ng.kg-1.min-1) and arachidonic acid (50-100 micrograms.kg-1.min-1) on the baroreflex control of heart rate in conscious dogs. Dogs were anesthetized with pentobarbital sodium and were instrumented using sterile surgical techniques. After recovery, baroreflex pressure-heart rate curves were constructed by varying arterial pressure with partial occlusions of the descending aorta or inferior vena cava. Intracoronary infusion of PGE2 significantly inhibited the maximum heart rate achieved during unloading of baroreceptors, attenuated the heart rate range, and decreased the maximum slope of the baroreflex curve; PGE2 had no significant effect on the minimum heart rate during hypertension. Intravenous infusion of PGE2 did not cause significant baroreflex inhibition, and pericoronary nerve block in three dogs prevented the effects of intracoronary PGE2. Intracoronary infusion of arachidonic acid had effects on the baroreflex control of heart rate similar to those of PGE2. The effects of arachidonic acid infusion were prevented by cyclooxygenase blockade. Thus intracoronary PGE2 and arachidonic acid inhibit the baroreflex control of heart rate most likely via stimulation of left ventricular receptors with vagal C-fiber afferents. The effects of arachidonic acid were secondary to synthesis of prostaglandins.

Animals↗
PubMed1989

A central mechanism of acute baroreflex resetting in the conscious dog.

The role of the central nervous system in the mechanism(s) involved in acute carotid baroreflex resetting was studied in six conscious, chronically instrumented, aortic-denervated dogs. Dogs were prepared for reversible vascular isolation of the carotid sinuses. Acute baroreflex resetting was induced by holding the left carotid sinus pressure (LCcsp) at a given value for 20 minutes using a pulsatile pressure control system while at the same time keeping the right carotid sinus pressure (RCSP) at a subthreshold level (approximately 40 mm Hg). At the end of the 20 minutes, the LCcsp) was reduced to approximately 20 mm Hg, and a baroreflex (RCSP-mean arterial pressure [MAP]) curve was generated on the right carotid sinus using static-step increases in carotid sinus pressure. At the control LCcsp of 100 mm Hg, the RCSP-MAP baroreflex had a threshold pressure (Pth) of 86.6 +/- 3.1 mm Hg and a set point pressure (Psp) of 104.7 +/- 2.5 mm Hg. Increasing LCcsp) to 140 mm Hg for 20 minutes caused these parameters for the right carotid baroreflex to increase. Pth and Psp increased by 18.4 +/- 4.0 and 14.2 +/- 3.0 mm Hg, respectively (p less than 0.05). The baroreflex curve, therefore, was shifted upward and to the right. Decreasing LCcsp to 60 mm Hg caused Pth and Psp to decrease by 24.7 +/- 5.0 and 18.1 +/- 2 mm Hg, respectively (p less than 0.05). The baroreflex curve was therefore shift downward and to the left. The percent of resetting of Pth and Psp was 46 +/- 9% and 36 +/- 8%, respectively, when LCcsp was 140 mm Hg.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

PGI2 attenuates baroreflex control of renal nerve activity by a vagal mechanism.

The present study was undertaken to determine whether left circumflex coronary artery (ic) administration of prostacyclin (PGI2) caused an inhibition of the baroreflex control of renal sympathetic nerve activity (RSNA). RSNA was recorded in 12 dogs. Baroreflex sensitivity of RSNA was assessed by infusion of either sodium nitroprusside or phenylephrine and by determining the slope of the mean arterial pressure-RSNA relationship. During nitroprusside infusion, intracoronary PGI2 depressed the baroreflex sensitivity by nearly 90% compared with intracoronary tris(hydroxymethyl)aminomethane (Tris) (P less than 0.002). In addition, the peak increase in RSNA during nitroprusside infusion was significantly inhibited during intracoronary PGI2 (57.9 +/- 6.4 vs. 21.2 +/- 3.0 spikes/s, P less than 0.05). There was no significant difference in the inhibition of RSNA during phenylephrine infusion when intracoronary PGI2 was compared with Tris. Both bilateral vagotomy and pericoronary lidocaine blocked the inhibitory effects of PGI2 on the baroreflex increase in RSNA. It is concluded from these data that exogenously administered PGI2 stimulates or sensitizes afferent endings within the supply of the left circumflex coronary artery to inhibit the baroreflex control of RSNA during evoked hypotension. These afferents traverse vagal pathways via the pericoronary nerves. The role of endogenous prostaglandins in modulation of baroreflex function via a cardiac reflex remains to be elucidated.

Animals↗
PubMed1988

Intracoronary infusion of prostaglandin I2 attenuates arterial baroreflex control of heart rate in conscious dogs.

Prostaglandin I2 (PGI2) is known to stimulate ventricular C fiber receptors resulting in a Bezold-Jarisch-like reflex. Also, cardiac receptor stimulation is known to interact with the expression of arterial baroreflexes. Therefore, experiments were performed to determine the effects of left circumflex coronary artery infusion of PGI2 on the baroreflex control of heart rate in conscious instrumented dogs. Dogs were instrumented chronically with an aortic catheter for the measurement of mean aortic pressure, hydraulic occluder cuffs on the descending aorta and inferior vena cava, a left ventricular catheter for the measurement of left ventricular pressure and heart rate, and a nonocclusive catheter in the left circumflex coronary artery. At the time of experimentation, arterial pressure was altered randomly in steps by partially inflating the occluders. Mean arterial pressure-heart curves (baroreflex curves) were constructed by fitting the data to a logistic curve by nonlinear regression. PGI2 infused into the left circumflex coronary artery at doses of 10, 20, and 50 ng/kg/min caused significant (p less than 0.05) inhibition of the maximum heart rate, heart rate range, and maximum slope of the curve compared to the control baroreflex curve obtained during intracoronary infusion of PGI2 vehicle. PGI2 had no significant effect on the minimum heart rate during hypertension. Since PGI2 is known to stimulate left ventricular receptors, these effects were most likely produced via stimulation of cardiac receptors. In additional experiments using beta 1-blockade with metoprolol or cholinergic blockade with atropine methyl bromide, it was shown that PGI2 attenuates baroreflex-mediated tachycardia by preventing parasympathetic withdrawal completely and by attenuating sympathetic stimulation by approximately 50%.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Initial experience with the argon laser in cutaneous vascular lesions.

An 18-month clinical study on the effects of argon laser in cutaneous vascular disorders in 41 patients carried out at the National University Hospital is discussed. The results confirmed the excellent response that can be achieved in lesions such as capillary hemangiomas, granuloma pyogenicum, cherry angiomas, telangiectasias and spider angiomas, but not in venous flare of the lower limbs. We are cautiously optimistic about its role in portwine stains; results are still being assessed. Complication rates so far have been relatively low with scarring observed in one patient.

Adolescent↗
PubMed1988

Prostaglandins mediate the increased sensitivity of left ventricular reflexes after captopril treatment in conscious dogs.

Captopril administration has been shown to result in the release of prostaglandins (PGs) in experimental animals and patients. Also, PGs, particularly prostacyclin (PGI2), have been shown to stimulate left ventricular receptor reflexes. Thus, the hypothesis that captopril administration results in sensitization of left ventricular reflexes via increased circulating levels of PGs was tested in conscious instrumented dogs. Left ventricular reflexes were stimulated by injecting veratridine into the left circumflex coronary artery through a nonocclusive catheter. Under control conditions, injection of veratridine resulted in a decrease in mean arterial pressure of -25 +/- 4.7% from a base line of 97 +/- 4.7 mm Hg and a decrease in heart rate of -28 +/- 3.7% from a base line of 91 +/- 6.6 beats/min. After administration of captopril, veratridine injection resulted in a decrease in mean arterial pressure of -43 +/- 4.9% and a decrease in heart rate of -51 +/- 8.5%, both significantly greater effects than before captopril (P less than .05); N = 7). Subsequent administration of the cyclooxygenase inhibitor, indomethacin (5 mg/kg), in the presence of captopril reversed the potentiation of the response to veratridine. Thus, after indomethacin, injection of veratridine decreased mean arterial pressure -29 +/- 4.4% and decreased heart rate -28 +/- 4.1%; changes not significantly different from the control response. Similar findings were observed in a separate set of experiments in which heart rate was held constant by cardiac pacing (N = 6).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

[Traditional Chinese and Western medicine in the treatment of 27 patients with malignant lymphoma].

Twenty-seven patients with malignant lymphoma (14 Hodgkin's disease, 9 histiocytosarcoma, 2 plasmacytoma, 2 lympholeucosarcoma) were treated by Ailin-injection plus Chinese herbal medicine. The latter's composition and dose varied depending on the clinical manifestations. All the patients had stage III and IV lesions. The total remission rate was 70.37% (complete remission 13 patients, partial remission 6 patients, no remission 8 patients). In addition, we also studied the suppressive effect of Ailin on transplanted tumor in vivo (S-180). The suppression rates were 36.09%, 48.80%, 32.67% by three repetitions with an average of 39.18% (P less than 0.002). They were 37.25%, 35.29% on S37 with an average of 36.27% (P less than 0.005). They were 46.53%, 44.56%, 51.35%, 45.95% on Ehrlich ascites tumor cells with an average of 47.09% (P less than 0.001). The clinical and experimental studies suggest that Ailin-1 has no serious side effects and is well tolerated by patients with malignant lymphoma at moderate or advanced stages. No toxic reactions were observed at the clinical dose. In the above combination therapy, the Chinese herbal medicine has obvious supplementary effect in the treatment of the patients' cachexia and immuno-suppression.

Adolescent↗
PubMed1987

Dynamic computed tomography and its application to ophthalmology.

In this review of 31 patients, dynamic CT is discussed as a valuable tool in the study of the dynamics of blood flow in patients with unexplained visual problems that may be related to ischemic optic neuropathy. Dynamic CT scans are obtained by rapid-sequence CT imaging during and following a rapid bolus injection of intravenous contrast medium. It demonstrates the initial passage of contrast material through the area of interest, thus giving a true picture of the degree of vascularity and the dynamics of blood flow.

Diagnosis, Differential↗
PubMed1986

Neuroradiological and electroencephalographic features in a case of temporal lobe status epilepticus.

A patient with medically intractable status epilepticus of temporal lobe origin is presented. A computed tomogram showed a low density area adjacent to the midbrain, possibly related to atrophy of the medial temporal lobe. Cerebral angiography revealed early filling veins and an anterior temporal blush. Magnetic resonance (MR) scanning (T2 weighted images) showed increased signal intensity in the region of the amygdala and anterolateral left temporal lobe. Ictal activity was recorded from scalp electrodes over the left temporal area, and many paroxysms were recorded from cortical surface electrodes. An anterior temporal lobectomy revealed only gliosis. The cerebral blood flow changes accompanying status epilepticus of focal origin are reviewed, and a possible relation of electroencephalographic, angiographic, and MR findings is discussed.

Adult↗
PubMed1986

The family.

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Culture↗
PubMed1984

Aphasia after left thalamic infarction.

We examined a 70-year-old woman who became aphasic after a left thalamic infarction. Computed tomographic scan showed injury that was largely limited to the ventral anterior and rostral ventral lateral thalamic nuclei. Speech was characterized by reduced voice volume, impaired auditory and reading comprehension, perseverations, intermittent use of jargon, fluctuations in the ability to perform confrontation naming, extraneous intrusions, verbal paraphasia, intact repetition skills, and fluent speech that was laconic but grammatically correct. We propose that the deficits after left thalamic injury can be grouped into the following four large clusters: extrapyramidal deficits (decreased or fading voice volume), deficits in lexical access (anomia, verbal paraphasia), deficits in vigilance (neologisms, intrusions, fluctuating performance, jargon, perseverations), and comprehension defects.

Aged↗
PubMed1984

Cardiopulmonary resuscitation at the Singapore General Hospital.

Effective use of Cardiopulmonary Resuscitation (CPR) saves lives both in and out of hospitals. Yet, in Singapore, this practical skill is rarely taught even within the medical community. Observations from a CPR pilot training programme at the Singapore General Hospital expose this glaring deficiency in our health system. Urgent remedial measures are needed.

Education, Continuing↗