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Biomedical subjects

R K Chan

Publications and source records attributed to R K Chan.

At least 73 records · Page 4Linked to original sources
PubMed1993

Condom knowledge, attitudes and use among patients attending the public STD clinic in Singapore.

Three hundred patients (255 males and 45 females) attending the public STD clinic in Singapore were interviewed regarding their frequency of condom use, attitudes towards condoms, problems related to condom use and places of purchase of the condoms. Among respondents with regular partners, 55.2% of males and 48.8% of females never used condoms, only 12.4% of males and 16.3% of females used condoms consistently. Among respondents with non-regular partners, only 2.2% of males used condoms consistently. The commonest reasons why male respondents did not use condoms consistently were that condoms decreased sensation, condoms made sex mechanical, the use of other forms of contraception, no condoms were available, and the perception that there was no risk of contracting STD/AIDS. Condoms were most commonly obtained from sex partners, supermarkets, roadside sundry shops and the Maternal & Child Health Clinics (MCHCs). About 8% of both males and females had experienced some problems with condoms before. Greater efforts to promote the practice of protected intercourse among the STD patient population as well as in the general population are required in order to control the spread of STD and AIDS in Singapore.

Adult↗
PubMed1992

Urinary tract infections in patients with diabetes mellitus.

We have endeavoured to determine whether there is any difference in the bacteriological pattern of UTI and the antibiotic sensitivity patterns of the pathogens concerned between diabetic and non-diabetic patients. Over a period of 1 year, a total of 287 diabetic patients (221 females and 66 males) with community-acquired and nosocomial urinary tract infections were studied. There were 265 patients (228 females and 37 males) without any predisposition to urinary tract infections (UTI) and who served as controls. Although Escherichia coli was the predominant organism in community-acquired UTI in diabetic patients, it was found significantly less than in the non-diabetic population (P less than 0.005). The percentage of Klebsiella species causing community-acquired UTI in diabetic patients was significantly higher than in non-diabetics (P less than 0.005). The antibiotic sensitivity patterns of the organisms in the two groups, however, were not significantly different. The organisms isolated from nosocomial UTI in diabetics showed a significantly greater preponderance of Klebsiella spp. and a significantly lower percentage of E. coli when compared to community-acquired UTI in diabetics (P less than 0.005). Klebsiella spp. in nosocomial UTI of diabetics showed an overall increase in resistance to antibiotics. At least a quarter of the isolates of Klebsiella spp. in nosocomial UTI were resistant to third-generation cephalosporins. Patients with diabetes mellitus appear to have an increased incidence of Klebsiella spp. as the pathogen in both community-acquired and nosocomial UTI. Antibiotic resistance in the organisms isolated from nosocomial UTI is greater than that related to community-acquired UTI in diabetic patients.

Aged↗
PubMed1992

Pefloxacin and ciprofloxacin in the treatment of uncomplicated gonococcal urethritis in males [corrected].

OBJECTIVE: To study the effectiveness of single-dose pefloxacin and ciprofloxacin in the treatment of uncomplicated gonococcal urethritis in males. SETTING: Department of STD Control, Kelantan Road, Singapore. METHOD: 160 male patients with uncomplicated gonococcal urethritis were assigned alternately to receive single oral doses of either pefloxacin 800 mg or ciprofloxacin 250 mg. RESULTS: Of the pefloxacin group 98.5% (65/66 patients) and of the ciprofloxacin group 98.6% (74/75 patients) were cured of gonorrhoea. The rates of post-gonococcal urethritis were 64.3% and 67.3% in the pefloxacin and ciprofloxacin groups, respectively. Both drugs were well tolerated and reported side-effects were minor and transient. There was a high incidence of penicillinase-producing gonococci (32.3%) and tetracycline resistant isolates with MIC > or = 2 mg/l (99.3%). High level tetracycline resistance (MIC > or = 16 mg/l) was found in 7.4% of isolates. CONCLUSION: The drugs in the dosages studied may be recommended for first-line treatment of uncomplicated gonococcal urethritis in males in Singapore. However, the emergence of bacterial resistance to the fluoroquinolones in the literature calls for vigilance in the monitoring of antimicrobial susceptibility [corrected].

4-Quinolones↗
PubMed1992

Community acquired urinary tract infections in Singapore: a microbiological study.

We studied 214 patients with culture proven community acquired infections. A total of 219 organisms were isolated, of which 68.2% were Escherichia coli, 10.1% Klebsiella sp and 5.5% Proteus mirabilis. Gram positive cocci accounted for 10.5% of organisms isolated. The majority of organisms isolated were sensitive to nalidixic acid (81.1%), nitrofurantoin (80.7%), cephalexin (74.7%) and trimethoprim-sulphamethoxazole (65.0%). Resistance to ampicillin was common (49.8%), as such the use of ampicillin in community acquired urinary tract infections will result in a high failure rate.

Adolescent↗
PubMed1991

Responses of cardiovascular neurons in the rostral ventrolateral medulla of the normotensive Wistar Kyoto and spontaneously hypertensive rats to iontophoretic application of angiotensin II.

In female pentobarbital-anesthetized Wistar Kyoto rats (WKY) and spontaneously hypertensive rats (SHR), changes in spontaneous discharges of cardiovascular neurons in the rostral ventrolateral medulla (RVL) in response to iontophoretic application of angiotensin II (Ang II) were studied and compared. It was found that iontophoretic application of Ang II to RVL increased the spontaneous neuronal activities of 30% of the cardiovascular neurons in both types of rats and that the increase was significantly greater in SHR than in WKY. In both types of rats, there was an increase in arterial blood pressure in response to iontophoretic release of Ang II to RVL. The pressor response was accompanied by tachycardia, which was significantly greater in SHR than in WKY. The present study provides evidence that Ang II acts directly on cardiovascular neurons in RVL, and in SHR, an enhanced sensitivity and responsiveness of the RVL cardiovascular neurons to Ang II may augment the sympathetic outflow from RVL and contribute to the genesis of hypertension.

Analysis of Variance↗
PubMed1991

Electrophysiological properties of neurons in the rostral ventrolateral medulla of normotensive and spontaneously hypertensive rats.

Single unit activities were recorded from the rostral ventrolateral medulla (RVL) of pentobarbital-anesthetized normotensive Wistar Kyoto rats (WKY) and spontaneously hypertensive rats (SHR). Throughout the recording period, arterial blood pressures of WKY (mean arterial pressure, MAP = 103.1 mm Hg) and SHR (MAP = 159.2 mm Hg) remained stable at the respective basal levels. The units recorded in this study were all spontaneously active and cardiac-locked. Two types of discharge patterns, namely single and double discharges, were identified. These single and double discharge units were found to distribute randomly in RVL. In WKY, 92.6% of RVL neurons exhibited single discharges whereas in SHR, the majority (57%) of RVL neurons exhibited double discharges. The mean firing rate of single discharge units in RVL of SHR was significantly higher than that of WKY, whereas the mean firing rate of double discharge units in WKY was similar to that of SHR. About half of the units studied were also tested for antidromic collision; all units tested could be antidromically activated from the intermediolateral column (IML) of the thoracic spinal cord and the lowest threshold sites were consistently localized within IML. In both groups of rats, the axonal conduction velocity of RVL neurons showed a bimodal distribution viz. the fast and slow conducting axons. The mean conduction velocities of each of these two groups of neurons in WKY and SHR were similar. Most of the double discharge units in WKY and SHR belonged to the fast conducting type.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Cardiovascular responses to electrical stimulation of the ventrolateral medulla of the spontaneously hypertensive rat.

Cardiovascular responses to electrical microstimulation of the ventrolateral medulla were investigated in both Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) under pentobarbital anesthesia. The threshold intensity required to elicit a change in blood pressure (BP) and the cardiovascular responses in these two groups of rats upon electrical stimulation were compared. It was found that the region with the lowest threshold intensities was located in the rostral ventrolateral medulla (RVL) and the threshold intensities were much lower in SHR than in WKY. Electrical stimulation of this brain region also resulted in a greater increase in BP during stimulation in SHR, compared to control. In SHR, upon termination of stimulation, the BP dropped to a level above the pre-stimulation level and this was followed by a prolonged, sustained elevation in BP before returning to the control level, whereas in WKY, the BP showed an initial drop to below the pre-stimulation level and then returned to the control level. These results suggest an enhanced responsiveness to electrical stimulation in SHR. Although the heart rate (HR) increased to a similar extent during electrical stimulation in both groups of rats, upon termination of stimulation WKY exhibited bradycardia followed by tachycardia before the HR returned to the pre-stimulation level, whereas SHR exhibited tachycardia which was maintained for a substantial period of time before returning to the pre-stimulation level. The results suggest a lower baroreceptor sensitivity in SHR. The change in HR/change in BP was smaller in SHR than in WKY, suggesting that the increase in HR may not contribute to the increase in BP during stimulation as much in SHR as in WKY.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Early clinical manifestations of HIV infection.

HIV infection produces a spectrum of illness from totally asymptomatic infection to AIDS. In between these two extremes, infected persons may manifest a variety of signs and symptoms. These include an acute infectious mononucleosis-like illness, progressive generalised lymphadenopathy, and numerous cutaneous and oral lesions. Whilst most of these conditions are not pathognomonic for HIV infection, certain features may indicate the possibility of an underlying HIV infection. Clinicians should be aware of these tell-tale signs.

HIV Infections↗
PubMed1990

Idiopathic bronchiolitis obliterans with organizing pneumonia in Singapore--first case report.

Idiopathic bronchiolitis obliterans organizing pneumonia (BOOP) has become accepted as a distinct disease entity. We report a patient who presented with the classical clinical, radiological and pathologic features of this uncommon condition. To our knowledge, this is first case to be reported in Singapore. This case also illustrates the difficulty of making a definitive diagnosis and emphasizes its therapeutic importance.

Aged↗
PubMed1990

Psychological and psychiatric investigations of HIV infection in Singapore.

A psychosocial study was carried out on 10 out of the 18 HIV positive persons who were under surveillance and receiving counselling at either Middle Road Hospital or the Communicable Disease Centre in February 1988. The results of the psychological testing and psychiatric findings are presented. All 10 were male: 9 of them were homosexual and 1 heterosexual. Only one had significant depressive symptoms at the time of study. All had fears about their infection being found out by others and of the stigma that this might bring to their families. Psychometric tests on memory function did not show any signs of visuo-verbal memory impairment but did reveal a possible indication of audio-verbal memory dysfunction.

Acquired Immunodeficiency Syndrome↗
PubMed1989

Cardiovascular effects of central administration of beta-endorphin in rats receiving neonatal injection of monosodium glutamate.

1. The effects of intracerebroventricular (i.c.v.) and intracisternal (i.c.) injection of beta-endorphin on arterial blood pressure (BP) in rats that received five intraperitoneal injections of monosodium glutamate (MSG) on alternate days in the first 10 days of life were studied. 2. beta-endorphin administered into the lateral ventricles caused a prolonged elevation in BP, whereas i.c. injection of the peptide resulted in an even longer lasting reduction in BP. In the MSG-treated rat, the prolonged hypertensive effect of i.c.v. injection of beta-endorphin was completely abolished, but the effect of i.c. injection of the peptide was the same as that in the control. Since MSG treatment destroyed selectively the structures around the third ventricle, it is suggested that these structures, including the arcuate nucleus, may be responsible for mediating the cardiovascular effects of beta-endorphin. 3. The effects of central administration of beta-endorphin were completely blocked by naloxone, which mainly antagonizes the actions of mu-receptor agonists and has no cardiovascular effects itself. The results suggest that mu-receptors may be involved in mediation of the effects of beta-endorphin on the cardiovascular system and that beta-endorphin in the brain may not exert a tonic influence on the cardiovascular functions.

Animals↗
PubMed1987

A decade of PPNG in Singapore.

It has been more than 10 years since PPNG was first diagnosed in Singapore. Since then the prevalence of PPNG has increased progressively, and is now maintained at between 30 to 35% of all gonococcal infections inspite of a decrease in the overall incidence of gonorrhoea in Singapore. PPNG infections have been recorded with all forms of complicated gonorrhoea including pelvic inflammatory disease, ophthalmia and disseminated gonococcal infection. Penicillin alone cannot be used to treat gonorrhoea. The use of antibiotics active against PPNG and NPPNG both in uncomplicated and complicated gonorrhoea as first-line therapy is now essential. The medical cost of treatment of gonorrhoea has increased by 100 to 200% as a result of the emergence of PPNG.

Cephalosporins↗
PubMed1985

Characterization of Saccharomyces cerevisiae mutants supersensitive to aminoglycoside antibiotics.

We describe mutants of Saccharomyces cerevisiae that are more sensitive than the wild type to the aminoglycoside antibiotics G418, hygromycin B, destomycin A, and gentamicin X2. In addition, the mutants are sensitive to apramycin, kanamycin B, lividomycin A, neamine, neomycin, paromomycin, and tobramycin--antibiotics which do not inhibit wild-type strains. Mapping studies suggest that supersensitivity is caused by mutations in at least three genes, denoted AGS1, AGS2, and AGS3 (for aminoglycoside antibiotic sensitivity). Mutations in all three genes are required for highest antibiotic sensitivity; ags1 ags2 double mutants have intermediate antibiotic sensitivity. AGS1 was mapped 8 centimorgans distal from LEU2 on chromosome III. Analyses of yeast strains transformed with vectors carrying antibiotic resistance genes revealed that G418, gentamicin X2, kanamycin B, lividomycin A, neamine, and paromomycin are inactivated by the Tn903 phosphotransferase and that destomycin A is inactivated by the hygromycin B phosphotransferase. ags strains are improved host strains for vectors carrying the phosphotransferase genes because a wide spectrum of aminoglycoside antibiotics can be used to select for plasmid maintenance.

Aminoglycosides↗
PubMed1983

Extracellular suppression allows mating by pheromone-deficient sterile mutants of Saccharomyces cerevisiae.

MAT alpha haploids with mutations in the STE13 or KEX2 gene, and MATa haploids with mutations in the STE6 or STE14 gene, do not mate with wild-type cells of the opposite mating type. We found that such mutants were able to mate with partners that carry mutations (sst1 and sst2) that cause cells to be supersensitive to yeast mating pheromone action. Mating ability of MAT alpha ste13 and MAT alpha kex2 mutants could also be restored by adding normal MAT alpha cells to mating mixtures or by adding just the appropriate purified pheromone (alpha-factor). Therefore, the mating deficiencies caused by the ste13 and kex2 lesions, and by inference, the ste6 and ste14 mutations, appear to result only from secretion of an insufficient amount of pheromone or a nonfunctional pheromone.

Animals↗
PubMed1982

Isolation and genetic analysis of Saccharomyces cerevisiae mutants supersensitive to G1 arrest by a factor and alpha factor pheromones.

Eight independently isolated mutants which are supersensitive (Sst-) to the G1 arrest induced by the tridecapeptide pheromone alpha factor were identified by screening mutagenized Saccharomyces cerevisiae MATa cells on solid medium for increased growth inhibition by alpha factor. These mutants carried lesions in two complementation groups, sst1 and sst2. Mutations at the sst1 locus were mating type specific: MATa sst1 cells were supersensitive to alpha factor, but MAT alpha sst1 cells were not supersensitive to a factor. In contrast, mutations at the sst2 locus conferred supersensitivity to the pheromones of the opposite mating type on both MATa and MAT alpha cells. Even in the absence of added alpha pheromone, about 10% of the cells in exponentially growing cultures of MATa strains carrying any of three different alleles of sst2 (including the ochre mutation sst2-4) had the aberrant morphology ("shmoo" shape) that normally develops only after MATa cells are exposed to alpha factor. This "self-shmooing" phenotype was genetically linked to the sst2 mutations, although the leakiest allele isolated (sst2-3) did not display this characteristic. Normal MATa/MAT alpha diploids do not respond to pheromones; diploids homozygous for an sst2 mutation (MATa/MAT alpha sst2-1/sst2-1) were still insensitive to alpha factor. The sst1 gene was mapped to within 6.9 centimorgans of his6 on chromosome IX. The sst2 gene was unlinked to sst1, was not centromere linked, and was shown to be neither linked to nor centromere distal to MAT on the right arm of chromosome III.

Alleles↗
PubMed1982

Physiological characterization of Saccharomyces cerevisiae mutants supersensitive to G1 arrest by a factor and alpha factor pheromones.

Saccharomyces cerevisiae MATa cells carrying mutations in either sst1 or sst2 are supersensitive to the G1 arrest induced by alpha factor pheromone. When sst1 mutants were mixed with normal SST+ cells, the entire population recovered together from alpha factor arrest, suggesting that SST+ cells helped sst1 mutants to recover. Complementation tests and linkage analysis showed that sst1 and bar1, a mutation which eliminates the ability of MATa cells to act as a "barrier" to the diffusion of alpha factor, were lesions in the same genes. These findings suggest that sst1 mutants, are defective in recovery from alpha factor arrest because they are unable to degrade the pheromone. In contrast, recovery of sst2 mutants was not potentiated by the presence of SST+ cells in mixing experiments. When either normal MATa cells or mutant cells carrying defects in sst1 or sst2 were exposed to alpha factor for 1 h and then washed free of the pheromone, the sst2 cells subsequently remained arrested in the absence of alpha factor for a much longer time than SST+ or sst1 cells. These observations suggest that the defect in sst2 mutants is intrinsic to the cell and is involved in the mechanism of alpha factor action at some step after the initial interaction of the pheromone with the cell. The presence of an sst2 mutation appears to cause a growth debility, since repeated serial subculture of haploid sst2-1 strains led to the accumulation of faster-growing revertants that were pheromone resistant and were mating defective ("sterile").

Cell Cycle↗