Biomedical subjects

D T Tan

Publications and source records attributed to D T Tan.

At least 73 records · Page 4Linked to original sources

PubMed1995

Hyperplasia of the muscularis propria in response to massive intestinal resection in rat.

Adaptation of the muscularis propria to intestinal resection is not well studied. Growing, 150- to 200-g Sprague-Dawley rats were divided into a resected group (R), which had 75% of the jejunoileum removed; a sham-resected group (SR); and a group of untreated controls (C). Food intake and weight gain were documented. Animals were killed on days 0, 10, 20, 30, or 40 (n = 14 animals for each day in each group). Small-intestinal length and jejunal circumference, wet weight/cm, thickness of the muscle layers, muscle morphometry, mg protein, and micrograms DNA per cm of the muscularis propria were measured. R rats had an initially greater food intake than SR or C animals, but the rate of weight gain was not different between groups. There was no significant increase in length of the residual intestine in R animals during the postoperative adaptive period, but circumference was significantly increased in R compared with SR or C animals. Wet weight/cm, mg protein, and micrograms DNA per cm of the muscularis propria were significantly greater in R compared with SR or C animals, but there was no change in thickness of the smooth-muscle layers in R versus SR or C rats. The number of cross-sectioned circular smooth-muscle cells/mm2 and the ratio of mg protein/micrograms DNA/cm length of muscularis propria were not different in R compared with SR or C animals. Intestinal resection resulted in a significant increase in circumference but not length of the residual intestine. A significant increase in the mass/cm, with no change in the number of cross-sectioned circular smooth-muscle cells/mm2 or in mg protein/micrograms DNA/cm of the muscularis propria, indicates that the adaptive response of muscularis propria is characterized by hyperplasia. This response potentially confers benefit to the organ and animal as a whole as a mechanism that permits structural and functional adaptation of the muscularis propria to resection.

Animals↗

PubMed1995

Massive intestinal resection depresses circular smooth muscle contractility in the rat.

To determine whether functional changes in in vitro contractility and in vivo gastrointestinal transit accompany the adaptive structural changes seen in jejunal circular muscle after massive intestinal resection, rats were subjected to either surgical resection of 75% of the mid-jejunoileum or a sham operation. Basal stress in response to stretch was similar for both groups on postoperative days 10, 20, 30, and 40. By day 10 after surgery, tissues from resected rats exhibited a significant reduction in bethanechol-stimulated tonic stress and in frequency of phasic contractions. The amplitude of spontaneous phasic activity was significantly increased; however, following cholinergic stimulation, the magnitude of the increase in the amplitude of phasic activity was significantly reduced. Experiments with tetrodotoxin (10(-6) M) indicated a myogenic origin to the reduction in bethanechol-stimulated tonic stress and the reduced frequency and altered amplitude of phasic contractile activity in resected animals. The tonic stress developed in response to depolarization with KCl did not differ significantly between sham-operated and resected rats. Transit studies showed no change in the rate of gastric emptying after resection but did reveal a significant reduction in the velocity of intestinal transit. Thus, following massive intestinal resection the bethanechol-stimulated tonic stress response and phasic contractile activity of circular smooth muscle are significantly reduced, concomitant with altered intestinal transit. The reduction in contractility in the resected animals may be due to an alteration at the level of the smooth muscle receptor and (or) its signal transduction pathway.

Animals↗

PubMed1995

Intestinal anaphylaxis: mediation of the response of colonic longitudinal muscle in rat.

Colonic smooth muscle function may be altered in food protein hypersensitivity reactions and could contribute to the clinical manifestation of diarrhea. To characterize such functional changes and elucidate the mediators and mechanisms involved. Hooded-Lister rats were sensitized by intraperitoneal injection of egg albumin (10 micrograms), and controls were sham sensitized with saline. Fourteen days later the contractility of longitudinally oriented distal colonic segments (mucosa intact) were studied in standard tissue baths in response to antigen (Ag) or other agents. After Ag exposure, a contractile response was documented in animals that were sensitized [specific immunoglobulin E (IgE) antibody levels > or = 1:64] and was specific for the sensitizing Ag. Mast cell involvement was suggested by a significant reduction in the number of granulated mucosal mast cells in sensitized tissues after Ag challenge and in the magnitude of the Ag-induced contractile response in the presence of mast cell stabilizers. The antigen-induced response was significantly and independently inhibited by both cyclooxygenase and lipoxygenase enzyme inhibitors and by leukotriene D4 and platelet activating factor receptor antagonists. The Ag-induced response was resistant to histamine and the 5-hydroxytryptamine antagonists, atropine and tetrodotoxin. These results suggest that the food protein-induced contraction of colonic longitudinal smooth muscle in the sensitized rat is due to IgE-mediated mast cell activation with the subsequent production and release of membrane-derived mediators that, in vitro, act directly on the smooth muscle.

Albumins↗

PubMed1995

Medical applications of scleral contact lenses: 1. A retrospective analysis of 343 cases.

The medical indications for, and outcome of scleral contact lens wear in 517 eyes of 343 patients attending a Scleral Contact Lens Clinic during a 5-year period from July 1988 to June 1993 were analysed. Keratoconus was the most common condition requiring scleral lens wear (36.2%), followed by aphakia (18.4%), postpenetrating keratoplasty (12.0%), irregular astigmatism secondary to corneal disease (12.0%), high myopia (12.8%), and ocular surface disorders (6.4%). The main indication was visual (85.8%), whereas therapeutic indications accounted for 8.2% of cases. Seventy-six percent of cases had previously failed with other types of contact lenses. The majority of patients were initially fitted with impression moulded polymethylmethacrylate (PMMA) lenses (90.5%); other scleral lens types included preformed PMMA lenses, preformed high Dk gas-permeable (GP) lenses, and a GP/PMMA hybrid scleral lens design. Initial scleral lens fitting was successful in 93.2% of cases, and 71% remained successful with a mean duration of 11.8 years' follow-up. Complications included corneal vascularisation (13.3% of eyes), episodes of corneal oedema (7.4%), corneal abrasion (3.1%), and giant papillary conjunctivitis (1.7%). In addition to 19 eyes initially fitted with GP lenses, there were 99 eyes initially wearing PMMA lenses that were subsequently refitted with GP scleral lenses.

Adolescent↗

PubMed1995

Medical applications of scleral contact lenses: 2. Gas-permeable scleral contact lenses.

The indications and outcome of the wear of gas-permeable (GP) scleral contact lenses in 118 eyes of 85 patients attending a Scleral Contact Lens Clinic during a 5-year period from July 1988 to June 1993 were analysed. Ninety-nine eyes (83.9%) were originally fitted with PMMA lenses and were subsequently changed to GP lenses, whereas 19 (16.1%) were fitted with GP lenses from the outset. The mean duration of GP scleral lens wear was 15.3 months, with a range between 3 and 58 months. The indications for refitting the cases previously wearing PMMA scleral lenses with GP material were related to problems of chronic hypoxia. Thirty-three eyes (26.8%) had previous episodes of corneal oedema, and of the 27 that had a minimum of 3 months' follow-up, none experienced further episodes of oedema. Of the 32 eyes (26%) that had developed corneal vascularisation associated with PMMA scleral lens wear, two eyes were noted to have significant vessel regression after a period of GP wear, whereas in the remainder of cases, vessels remained static and nonprogressive. Thirty additional eyes (24.2%) experienced inadequate wear times associated with discomfort, and in these eyes the change to GP scleral lenses produced a statistically significant reduction in the inability to wear lenses beyond 4 h (p < 0.05).

Adolescent↗

PubMed1995

Corneal ulcers in two institutions in Singapore: analysis of causative factors, organisms and antibiotic resistance.

The aim of this study was to determine the causative factors, organisms and antibiotic resistance in patients with bacterial keratitis in Singapore. We analysed retrospectively 103 cases of bacterial keratitis admitted to the Singapore General Hospital or the Singapore National Eye Centre during a 21-month period from March 1992 to December 1993. Contact lens wear represented the largest single predisposing factor (35 eyes, 34.0%), followed by ocular trauma (28 eyes, 27.2%) and pre-existing ocular disease (28 eyes, 27.2%). Thirteen of the twenty-eight cases of trauma-related keratitis were work-related injuries. Gram-negative organisms formed the largest group (41 cultures, 80.4%), with Pseudomonas aeruginosa being the most common organism identified (30 eyes). Pseudomonas was also responsible for 78.6% of all contact lens ulcers (11 out of 14 eyes). Resistance to gentamicin was only encountered in 1 case of Proteus mirabilis keratitis. All cases of Pseudomonas infection and 3 of the 10 Gram-positive cases were also resistant to chloramphenicol. All Gram-positive cases were sensitive to cephalosporins. Contact lens wear and ocular trauma are the major preventable risk factors for bacterial keratitis in young sighted eyes in Singapore. Gentamicin continues to be the antibiotic of choice for Gram-negative corneal infections in view of the low incidence of resistance. The routine use of chloramphenicol as the topical antibiotic of choice for corneal infection is not recommended due to the high resistance in Gram-positive and Gram-negative organisms locally.

Adult↗

PubMed1993

Early central posterior capsular fibrosis in sulcus-fixated biconvex intraocular lenses.

A series of 228 eyes implanted with one-piece all poly(methyl methacrylate) (PMMA) biconvex posterior chamber intraocular lenses was examined for posterior capsule opacification. One hundred forty-one eyes (61.8%) had opacification at an average postoperative period of 19.7 months. Seventy eyes (30.7%) developed an unusual form of early central posterior capsular fibrosis (ECPCF), which was confined to the capsulorhexis opening, sparing the peripheral aspect of the anterior and posterior capsules. Risk factors for developing this form of opacification were close apposition of peripheral anterior and posterior capsules caused by placing a posteriorly vaulted biconvex optic anterior to a capsulorhexis opening smaller than the optic diameter. This opacification occurred most often in cases of haptic fixation in the ciliary sulcus. The cumulative capsulotomy rate in this series was 5.26% at three months, 9.1% at 12 months, and 13.2% at 20 months. Of the ECPCF cases, 34.3% eventually required neodymium: YAG (Nd:YAG) laser capsulotomy; the capsulotomy rate for ECPCF was 4.8 times higher than that for Elschnig pearls. Early onset of ECPCF (average onset = 19.4 weeks) resulted in early Nd:YAG capsulotomy (average = 8.0 months after surgery). One-piece all-PMMA biconvex intraocular lenses may promote early central fibrosis of the posterior capsule if the lens optic is anterior to a capsulorhexis opening smaller than the optic diameter. The early onset of this form of opacification predisposes to earlier Nd:YAG capsulotomy with a higher risk of complications.

Adult↗

PubMed1993

Neural modulation of canine duodenal bile acid delivery in the interdigestive and postprandial periods.

The neural modulation of gallbladder filling-emptying and duodenal delivery of canine hepatic biliary output was studied in conscious dogs using transient cold blockade or transection of the cervical vagosympathetic nerves previously isolated in skin loops on either side of the neck. Gallbladder filling-emptying was defined as the algebraic difference between a steady-state rate of hepatic secretion [established by a continuous intravenous infusion of [14C]taurocholic acid (TCA)] and the duodenal rate of delivery of [14C]TCA (measured by duodenal marker perfusion). Duodenal motility was recorded manometrically. Experiments in the fasted and fed state were performed under control conditions, during cold blockade, and after transection of the cervical vagosympathetic nerves. Under control conditions: 1) during fasting, the majority of hepatic [14C]TCA output was stored in the gallbladder during the first half of the migrating myoelectric complex (MMC). An increased rate of duodenal delivery and partial gallbladder emptying occurred before phase III of the MMC. 2) Feeding induced an immediate increase in duodenal bile acid delivery and gallbladder emptying. After cold blockade or transection: 1) partial gallbladder emptying before phase III of the MMC was abolished. 2) The immediate postprandial increase in duodenal bile acid delivery and gallbladder emptying was abolished even when the animal received a continuous duodenal infusion of the duodenal aspirate of another fed animal (to control for the effect of impaired gastric emptying after cold blockade). In addition, cold blockade significantly reduced the effect of an exogenous infusion of cholecystokinin octapeptide on gallbladder emptying. These results suggest that neurons in the canine cervical vagosympathetic nerves play a major role in the regulation of rhythmic partial emptying of the gallbladder in the interdigestive period, coordinate a cephalic phase of postprandial gallbladder emptying, and are important in mediating the effects of cholecystokinin on the gallbladder during the gastric and enteric phases of postprandial gallbladder emptying.

Animals↗

PubMed1993

A retrospective study of cataract surgery in the Singapore General Hospital in 1990.

Nine hundred and ninety-five consecutive cases of cataract extraction with or without lens implantation performed within the first three months of 1990 in the Singapore General Hospital were examined retrospectively. Of the 995 cases, 874 (87.84%) were deemed to have adequate postoperative evaluation at an average of 12.5 months. Of these cases, 79.52% (695 eyes) obtained a visual acuity of 6/12 or better. When cases with pre-existing causes of poor vision were excluded, 90.25% of cases obtained a visual acuity of 6/12 or better. If potentially treatable causes of postoperative poor vision (such as posterior capsule opacification awaiting Nd:YAG laser capsulotomy and high astigmatism prior to suture removal) were further excluded from analysis, this figure would rise to 93.66%. The incidence of posterior capsule rupture was 1.4%. Factors affecting visual success included patient age, lens hypermaturity and duration of surgery.

Adolescent↗

PubMed1993

Advanced cataract in Singapore--its prognosis and complications.

A retrospective study of 995 eyes that had undergone cataract surgery between January and March 1990 revealed that one in 20 (50 eyes) were advanced cataracts which, by our definition, included hypermature, Morgagnian and intumescent cataracts. Thirty percent of these cases suffered from cataract-related complications preoperatively: phacomorphic glaucoma (12/50 eyes), phacolytic glaucoma (1/50 eyes), and subluxed cataract without trauma (2/50 eyes). Cataract surgery in these advanced cataracts produced significantly poorer results than the rest. One in four eyes failed to achieve visual acuity of 6/12 or better (best corrected) postoperatively, while one in eight eyes did not improve beyond Hand Movement vision. The main reason for poor visual results was lens-induced glaucoma (80%).

Aged↗

PubMed1993

Will patients with contact lens problems accept excimer laser photorefractive keratectomy?

One hundred six patients who presented to the Singapore National Eye Centre with contact lens related problems from June 1992 to September 1992 were given information about photorefractive keratectomy (PRK) and asked to give their reactions to the procedure. The patients in the study were largely female myopes (89%) with diverse contact lens problems. Forty-seven of 106 patients (44%) indicated they would consider PRK for themselves. Asked why, 37 patients (79%) cited the convenience of not needing spectacles or contact lenses. Of the 59 patients (56%) who were not interested in PRK, 46 patients (78%) expressed fears about possible complications; others were not convinced of the efficacy of PRK. The group of patients interested in PRK was comprised of more males (P = 0.0099) and more high myopes (P = 0.036). Of the 47 patients keen on PRK, 38 patients fit the surgical criteria. At 3 months after conclusion of the study, only two patients had undergone PRK.

Adolescent↗

PubMed1992

Yersinia enterocolitica enteritis affects rabbit intestinal longitudinal smooth muscle function.

To determine whether Yersinia enterocolitica (YE) enteritis has an effect on the biomechanical properties of intestinal smooth muscle, New Zealand White rabbits (600-900 g) were divided into an infected group (n = 9) and sham-infected animals fed ad libitum (n = 9), or pair fed with the infected group (n = 9). Animals were inoculated with 10(10) organisms of YE in 10 ml NaHCO3 (infected group) or 10 ml NaHCO3 (sham-infected control and pair-fed groups) at time 0. Daily food intake, weight gain, and YE excretion were noted. Six days later animals were killed and longitudinal smooth muscle strips prepared from proximal (P), medial (M), and distal (D) segments of intestine in each treatment group. Isometric tension was recorded in tissue baths perfused with oxygenated Krebs solution and 10(-6) M tetrodotoxin. Basal and active (the response to 10(-5) M carbachol) length-tension curves were generated. Then, with the muscle strips stretched to their optimum length for tension development, the dose response to carbachol and to graded depolarization with KCl was determined. Infected animals had a significantly reduced food intake and weight gain compared with controls. The development of basal tension with stretch was not significantly different in infected compared with control or pair-fed tissues from the same site.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Assay of 3-hydroxy-3-methylglutaryl CoA reductase activity using anionic-exchange column chromatography.

A rapid, easy, and sensitive method is described in this paper for the assay of 3-hydroxy-3-methylglutaryl CoA (HMG CoA) reductase, a key enzyme in cholesterol biosynthesis. [14C]HMG CoA was used as the substrate and the product formed, i.e., [14C]mevalonate, was allowed to be converted to its lactone form (mevalonolactone) in the presence of HCl. The reaction mixture was applied to a column containing an anionic exchanger. The column was made up of QAE-Sephadex (A25, formate form) packed to a height of 4 cm in Pasteur pipets. Under these conditions, mevalonolactone was not retained by the column and was eluted with ammonium formate solution while HMG CoA, being negatively charged, was retained by the gel and eluted by HCl above 0.05 M. Determination of the amount of radioactivity in mevalonolactone was then used to quantitate the activity of HMG CoA reductase. This assay has been successfully used for determining the activity of this enzyme in a microsomal fraction prepared from the liver of the rat.

Anions↗

PubMed1991

Effect of a palm-oil-vitamin E concentrate on the serum and lipoprotein lipids in humans.

The effect of a capsulated palm-oil-vitamin E concentrate (palmvitee) on human serum and lipoprotein lipids was assessed. Each palmvitee capsule contains approximately 18, approximately 42, and approximately 240 mg of tocopherols, tocotrienols, and palm olein, respectively. All volunteers took one palmvitee capsule per day for 30 consecutive days. Overnight fasting blood was taken from each volunteer before and after the experiment. Serum lipids and lipoproteins were analyzed by using the enzymatic CHOD-PAP method. Our results showed that palmvitee lowered both serum total cholesterol (TC) and low-density-lipoprotein cholesterol (LDL-C) concentrations in all the volunteers. The magnitude of reduction of serum TC ranged from 5.0% to 35.9% whereas the reduction of LDL-C values ranged from 0.9% to 37.0% when compared with their respective starting values. The effect of palmvitee on triglycerides (TGs) and HDL-C was not consistent. Our results show that the palmvitee has a hypocholesterolemic effect.

Body Weight↗

PubMed1991

Dietary fats and oils in cardiac arrhythmia in rats.

The effect of long-term feeding of various dietary fats and oils on cardiac arrhythmia was studied in an animal model of sudden cardiac death. After confirmation that a dietary supplement of saturated animal fat (SF) increased the animals' susceptibility to develop cardiac arrhythmia under ischemic stress whereas the polyunsaturated fatty acids of sunflower seed oil (SSO) reduced this susceptibility, we found that diets supplemented with either chemically refined palm oil (PO-I) or physically refined palm oil (PO-II) gave results that were generally intermediate in value between the SF and the SSO groups. However, during reperfusion of a previously ischemic heart, both PO-I- and PO-II-supplemented diets appeared to be as effective as SSO in reducing ventricular premature beats. In addition, the incidence of animals displaying severe ventricular fibrillation was much less after palm-oil feeding than it was after SF feeding. These preliminary results warrant further investigation of the potential antiarrhythmic effects of commercial palm oil.

Animals↗

PubMed1991

Singapore General Hospital's experience in corneal grafting.

This is a retrospective study of 56 corneal grafts that was done in the Singapore General Hospital (SGH) between 1980 and 1989. These cases were analysed and it was found that there was a male predominance of about 2:1. There was a rather even spread among the various age groups except for a slightly higher incidence in the 20-29 year age group. There was a drastic drop in the number of grafts done after the year 1987 and this was attributed to the reluctance to accept donor corneas from Sri Lanka as there was the danger of the AIDS transmission through the donor material. The most number of grafts were done for patients with infection as a cause for corneal opacities, followed closely by keratoconus. There was a high incidence of graft rejection as almost 20 out of the 56 developed rejection. However, the visual results proved to be good with 27 obtaining at least 6/12 vision post operatively. This article outlines the need for more stringent pre-operative evaluation of both the donor material as well as the host patient in order to reduce the incidence of graft rejection and, hence, increase the overall success rate.

Age Factors↗

PubMed1984

Courtship ultrasonic vocalizations in male Swiss-Webster mice: effects of hormones and sexual experience.

The effects of testosterone and its metabolites (estradiol and 5 alpha-dihydrotestosterone) on male mouse ultrasonic vocalizations were investigated using Swiss-Webster mice. In the first experiment daily treatment with 50 micrograms or 200 micrograms of testosterone propionate (TP) restored ultrasonic calling in castrated sexually naive males. Treatment with 200 micrograms of dihydrotestosterone propionate (DHTP) also activated ultrasound production, but treatment with 50 micrograms of DHTP or estradiol benzoate (EB 0.5 microgram and 2 micrograms/day) failed to have a significant effect on this measure. In experiment two, the animals used had shown male sexual behavior before castration. These sexually experienced males showed a marked reduction in ultrasound production after castration but significantly increased ultrasound production after daily treatment with either TP (50 micrograms or 200 micrograms), DHTP (50 micrograms or 200 micrograms) or 2 micrograms of EB. Hormones that facilitated ultrasound calling also activated other components of male sexual behavior in this and previous studies with Swiss-Webster mice. The results indicate that hormone dose and precastration sexual experience interact to determine the effects of postcastration treatment on male vocalizations.

Animals↗

PubMed1975

Gastric mucosal lacerations from blunt trauma to the abdomen.

A 17-year old, Caucasian male, high school student sustained gastric mucosal lacerations from blunt trauma to the abdomen during a football game with associated severe upper gastrointestinal bleeding. The lacerations were diagnosed by endoscopy and treated conservatively with uneventful, rapid and complete recovery.

Abdominal Injuries↗