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Biomedical subjects

A Chan

Publications and source records attributed to A Chan.

At least 289 records · Page 16Linked to original sources
PubMed1983

Cardiac beri beri--an old disease in modern Singapore--2 case reports.

This case report presents two Malay brothers who developed acute high output congestive cardiac failure within two weeks of each other. They gave a history of excessive alcohol consumption for six months, and glue sniffing for one year. The serum pyruvate levels were elevated in both prior to treatment. Haemodynamic studies were done in the second brother, and measurements obtained before, during and after treatment. A dramatic clinical response to parenteral thiamine was observed in both patients in the acute stage. The haemodynamic study was repeated after three months and showed a normal pattern.

Adult↗
PubMed1982

Norepinephrine-induced elevation of acetyl coenzyme A in rat pineal glands in culture.

A micromethod for the determination of acetyl coenzyme A was developed and the relationship between the concentration of acetyl coenzyme A and the activity of rat pineal serotonin N-acetyltransferase was studied. Acetyl coenzyme A was determined by converting it into N-acetylserotonin using rat liver serotonin N-acetyltransferase. Subsequently, the hydroxy group of N-acetylserotonin was O-methylated by hydroxyindole-O-methyltransferase and S-[methyl-3H]adenosyl-l-methionine to form [3H]melatonin, which was then conveniently separated from S-[methyl-3H]adenosyl-l-methionine by thin-layer chromatography. The amount of radioactivity in melatonin is a measure of acetyl coenzyme A concentration. This method is sensitive and specific, since it can detect as low as 5 pmol of acetyl coenzyme A but not structurally related substances such as coenzyme A, adenosine diphosphate, cysteamine, D-panthothenic acid, or sodium acetate. After treating cultured rat pineal glands with l-norepinephrine (10 microM) for 6 hr, the concentration of acetyl coenzyme A was increased significantly from 3.26 +/- 0.37 to 10.24 +/- 0.93 pmol/gland, while the activity of serotonin N-acetyltransferase increased 68-fold. This result suggests that acetyl coenzyme A may play an important role in the norepinephrine-induced induction of serotonin N-acetyltransferase. Sensitivity and adaptability of this method can be utilized to measure acetyl coenzyme A in discrete regions of rat brain and in experimental conditions in which micromeasurement of acetyl coenzyme A may be required.

Acetyl Coenzyme A↗
PubMed1982

Evaluation of extracranial carotid artery disease by ultrasonic duplex scanning: a clinical perspective.

The development of noninvasive methods of extracranial carotid artery evaluation over the past decade has led to questions as to their usefulness in daily clinical practice. They have generally been proposed for use in screening asymptomatic patients with bruits or those about to undergo major operative procedures. Since patients with focal symptoms are considered candidates for arteriography, noninvasive tests in this situation may be redundant. However, as the accuracy of the imaging and pulsed Doppler methods has improved, it is appropriate to re-examine this question. Based upon our experience, it is our current feeling that initial screening using ultrasonic Duplex scanning does have a place in symptomatic patients and can be shown to be cost effective.

Angiography↗
PubMed1982

Studies of testicular and epididymal damage in relation to the occurrence of antisperm antibodies.

The relationship between testicular histopathology, follicle stimulating hormone levels, sperm density and the presence of antisperm antibodies was investigated. There was no association between damage to the seminiferous tubules and the presence of agglutinating or immobilising antisperm antibodies. In 2 patients with congenital obstructive azoospermia and pre-biopsy circulating antisperm antibody there was extensive lymphocytic, macrophage and plasma cell infiltration, fibrosis and perivasculitis on epididymal biopsy. Breaches in the blood epididymis barrier are worthy of further investigation when considering the genesis of antisperm antibodies.

Autoantibodies↗
PubMed1982

Serotonin N-acetyltransferase and its regulation by pineal substances.

The regulation of activity of serotonin N-acetyltransferase (NAT) in pineal glands of various mammalian hierarchies may be species-specific, mediated by different mechanisms and brought about by interactions with dissimilar receptor sites. In addition to norepinephrine, serotonin and gamma-aminobutyric acid (GABA) seem to modulate NAT activity. Furthermore, preliminary studies provide evidence for the existence in pineal gland of a thermo-stable proteinaceous substance (NIS) which inactivates NAT but not other enzymes involved in the synthesis of melatonin. Inactivation of NAT by NIS is blocked by addition of 0.5 mM acetyl coenzyme A, but not coenzyme A, 0.1 M NaF or 4 mM beta-mercaptoethanol. In addition, protein dephosphorylation and disulfide exchange mechanisms are not involved in this NIS-mediated inactivation of NAT. In rat brain, the inactivating substance was found only in the pineal gland and was undetectable in other tissues. We postulate that the collective interaction among norepinephrine, serotonin, GABA, acetyl coenzyme A, NIS and NAT may regulate the synthesis of melatonin in the pineal gland.

Acetyl Coenzyme A↗
PubMed1981

Effects of norepinephrine on pineal tryptophan hydroxylase, using an improved [14C]CO2-trapping microtechnique.

The synthesis of many biogenic amines involves hydroxylation and/or decarboxylation reactions. These enzymes are often measured by trapping and be determining the concentrations of their end products [14C]CO2, from carboxyl-labeled substrates. An improved [14C]CO2-trapping technique has been developed for microassay of tryptophan hydroxylase activity. This technique allows hydroxylation and decarboxylation reactions to be carried out sequentially in microculture tubes containing reaction mixtures in less than 50 microliter. The incubation vessel consists of two microculture tubes connected by a latex tubing serving as a sleeve. One of the two microculture tubes were used to carry out enzymatic reactions and the other one was filled with CO2-trapping agent to trap [14C]CO2. The utility of this technique was tested by measuring the effects of biogenic amine on tryptophan hydroxylase in bovine pineal explants in culture. The bovine pineal tryptophan hydroxylase was found to have a specific activity of 8.93 pmol/mg protein/min, and its activity was linear with respect to both incubation time and to protein concentrations. In addition, treatment with norepinephrine of both rat pineal gland and bovine pineal explants in culture for 2, 4, and 6 hr had no effect on the activity of tryptophan hydroxylase. It is believed that this technique may be adapted easily to measure numerous CO2-generating enzymatic reactions whenever the amounts of protein or the size of tissue demands the application of a microtechnique.

Animals↗
PubMed1981

Evidence for existence of a serotonin N-acetyltransferase inactivating substance in rat pineal gland.

This study provides evidence for the existence of an inactivating substance in pineal glands, which may be responsible for the rapid inactivation of serotonin N-acetyltransferase seen in vivo and in vitro. This serotonin N-acetyltransferase inactivating substance enhances the thermal inactivation of the norepinephrine-stimulated serotonin N-acetyltransferase activity in rat pineal homogenate. Inactivation of serotonin N-acetyltransferase by the inactivating substance and the thermal inactivation of serotonin N-acetyltransferase at 37 degrees C exhibit the following identical properties. Both processes affect serotonin N-acetyltransferase without effect on other melatonin-related enzymes; can be blocked by addition of 0.5 mM [3H] acetyl CoA, but not coenzyme A in the preincubation mixture; and were unaffected by 0.1 M NaF or 4 mM beta-mercaptoethanol. These data are interpreted to suggest that protein dephosphorylation and disulfide exchange mechanisms are not involved in either inactivation processes. Unlike serotonin N-acetyltransferase, which is highly thermo labile, the inactivating substance is thermo stable at 37 degrees C for 40 minutes. In rat, the inactivating substance was found only in the pineal gland and was undetectable in other tissues. The inactivating substance is protein in nature, since it is not dialyzable but is inactivated by boiling or treatment with trypsin. The substance, which was able to inactivate serotonin N-acetyltransferase isolated from rate liver, exhibited no diurnal variation and its activity in rat pineal gland in culture was not influenced by norepinephrine. It is postulated that the interaction among acetyl coenzyme A, serotonin N-acetyltransferase and serotonin N-acetyltransferase inactivating substance may collectively regulate the synthesis of melatonin in pineal gland.

Acetyl Coenzyme A↗
PubMed1981

Perioperative preservation of myocardial ultrastructure and high-energy phosphates in man.

To establish whether hypothermic crystalloid potassium cardioplegia given in multidose fashion provides adequate preservation of myocardial ultrastructure and high-energy phosphates, we studied 25 patients with an ejection fraction of 50% or higher who were undergoing cardiac procedures. Eight patients had three biopsy specimens taken from the left ventricular apex for determination of adenosine triphosphate (ATP) and creatine phosphate (CP). Specimens were taken immediately prior to aortic cross-clamping, immediately after the release of the aortic cross-clamp, and 30 minutes after the release of the cross-clamp. Seventeen patients had six specimens taken form the left ventricular apex at the above-stated times, three for ATP and CP determination and three additional specimens for electron microscopy. One patient had a small perioperative infarction and another patient died on the fifth postoperative day of an aortic dissection. The mitochondria on the electron microscopic specimens were graded on a scale from 0 to 4 (4 = severe changes). There was no significant difference in the mitochondrial scores. The preservation oh high-energy phosphates was less complete. ATP was reduced to 78% (3.4.2) of control and CP was reduced in the immediate postclamp period to 32% (081/2.5)of control. The difference are particularly significant if one looks at patients whose aortic cross-clamp time was 90 minutes or more (12 patients). In this group, ATP an CP preservation were 71% of control (3.33/4.60 mmoles/kg. wet weight) and 53% of control (l.48/2.81), 30 minutes after clamp removal (p equal to or less than 0.01). We conclude that hypothermic potassium cardioplegia gives excellent preservation of the myocardial ultrastructure in man. However, the preservation of high-energy phosphates with this technique is imperfect.

Adenosine Triphosphate↗
PubMed1980

The kinetics of norepinephrine-induced stimulation of serotonin N-acetyltransferase in bovine pineal gland.

Fresh pineal explants were cultured in medium 199 containing 0.1 mg/ml of ascorbic acid, 2 mM glutamine, and 0.1% BSA in 95% O2 and 5% CO2 from 1 to 10 h. Norepinephrine (10 micrometers) increased serotonin N-acetyltransferase (NAT) activity from 2.36+ / -0.23 to 6.98+ / -0.46 pmol product produced/mg protein/min (unit), without influencing tryptophan hydroxylase, 5-hydroxytryptophan decarboxylase, monoamine oxidase, or hydroxyindole-O-methyltransferase. Dibutyryl cyclic AMP (1 mM) also stimulated NAT from 1.39+ / -0.12 to 4.33+ / -0.65 U. The norepinephrine-induced stimulation of NAT was blocked by GABA (10 micrometers), by dl-propranolol (20 micrometers), by cycloheximide (30 micrometers), by puromycin (20 micrometers), but not by actinomycin D (10 micrometers). Comparing the kinetics of native and stimulated NAT, the occurred changes in Vmax with regard to both substrates - tryptamine (from 0.885 to 3.44 U) and acetyl CoA (from 3.45 to 9.10 U) - without changes in Km with respect to both tryptamine (Km = 5 micrometers) and acetyl CoA (Km = 50 micrometers). The results of this investigation are interpreted to indicate that the norepinephrine-induced stimulation of NAT may be due to enhanced protein synthesis involving translational or post-translational events. Furthermore, the enhanced protein synthesis is coupled through activation of beta-receptor and cyclic AMP mediated actions in pineal gland. The precise interrelationship between GABA and norepinephrine in mediating and perhaps in controlling the biological events in the bovine pineal gland still awaits clarificaton.

Acetyltransferases↗
PubMed1980

Aldolase isoenzyme patterns during human ontogeny and in lung, kidney and breast cancer.

Enzyme patterns characteristic of fetal tissue have been noted in some experimental tumor models, particularly in hepatomas. In this study we undertook to determine whether biochemical evidence of a similar reversion could be detected in tumors of other human organs. As marker, we chose to use the aldolase isoenzymes A, B and C, for which distinct adult and fetal tissue patterns have been described. Using monospecific antibodies, we determined the aldolase isoenzyme pattern in a variety of human organs ranging in age from 14 to 40 weeks of gestation, in the 2- to 3-month postnatal period and in adults. In addition, 19 breast cancers, 19 primary lung cancers and 8 kidney cancers were examined. Our studies on breast cancer revealed three apparently distinct groups -- one showing primarily the A isoenzyme type (6 cases), a second containing mainly A with considerable quantities of B and C isoenzymes (9 cases) and a third group (4 cases) which may contain a different isoenzyme altogether since the combined activity of the three known forms was less than 100% in each case. In lung cancer, fetal characteristics could be substantiated since in fetal and adult lung tissue, the isoenzyme pattern is almost identical; 3 out of 19 cases showed substantial quantities of the B isoenzyme. In kidney tumors, a reversion to the A form with an appreciable fraction of the C form was found, which is similar to the fetal pattern.

Adenocarcinoma↗
PubMed1979

A Comparison of Coulter ZBI and Fisher Autocytometer II Hematological Values in 28 Mammalian Species at the Metropolitan Toronto Zoo.

One hundred and thirty-three blood samples from twenty-eight mammalian, nondomestic species were analyzed using both the Coulter ZBI and Fisher Autocytometer II. The WBC, RBC and Hb values for each species from both machines, were compared. The study indicated that for 27 species there was no significant difference (P > 0.05) between machines for the WBC. Twenty-one species showed no significant difference (P > 0.05) in the RBC results. Only one species exhibited a significant difference (P > 0.05) between machines in the hemoglobin value obtained.

Journal Article↗
PubMed1978

Specific cation effects on conformational transitions of DNA in aqueous solutions.

The circular dichroism (CD) and absorption spectral properties of calf thymus DNA have been examined in aqueous solutions containing varying concentrations of MgCl2, CaCl2, MnCl2, ZnCl2 and CoCl2. When the CD spectra were analyzed by methods previously described (Hanlon, S., Brundno, S., Wu, T.T. and Wolf, B. (1975) Biochemistry 14, 1648--1660), it was found that the spectral changes observed between 0 and 0.1 molal concentrations of each salt could be satisfactorily accounted for as a linear combination of two independent spectral components. One of these components had the spectrum which we had previously obtained in dilute solutions of NaCl (0.01-0.04 molal) and in 0.2 M tetramethyl ammonium chloride and attributed to a B-like structure. The other spectral endpoint was similar but not identical to the C spectrum obtained in the monovalent series. These differences were particularly pronounced for the transition metal ions, Mn2+, Zn2+ anc Co2+. Since significant band shifts were also observed in the absorption spectra of DNA in the presence of these transition metal ions, we have concluded that the differences observed between the C spectrum previously reported and that found for these ions is attributable to changes in the absorption properties of the monomers due to cation association, rather than dramatic differences in comformational properties of the C secondary structure of DNA in the presence of these ions. The greater efficiency of these divalent ions compared to the monovalent ions previously studied in effecting the B leads to C transconformational reaction is attributed to the more effective screening of electrostatic interactions, both along the phosphate backbone, and between sites on the bases which bear partial negative charges and the negatively charged phosphate groups. In the light of these present results, we believe that it is this electrostatic factor which is primarily involved in effecting the transition from a B to a more C-like state. The role of dehydration is viewed as a subsidiary one which facilitates better ion association, especially at the weaker base sites, thus effecting better damping of the repulsive electrostatic interactions.

Animals↗
PubMed1976

Comparison of the phosphorus magnetic resonance and circular dichroism properties of calf thymus DNA and chromatin.

Dual measurements of the 31P magnetic resonance spectra and the circular dichroism spectra have been made on calf thymus DNA and purified chromatin. The 31P magnetic resonance signals for all samples fell at 1.2 +/- 0.1 ppm relative to 85% orthophosphoric acid. The full width at half-height of the signal of samples in which the molecular weight of the native DNA component was in the 2-9 X 10(6) range was ca. 50 Hz. This bandwidth was reduced dramatically to ca. 20 Hz by reducing the molecular weight to 140 000 (by sonication) or by heat denaturation of the high-molecular-weight DNA. The position of the signal and the bandwidth of the chromatin samples did not differ significantly from that of the DNA samples of comparable molecular weight and state of nativity. The intensities of the chromatin signals, however, were all less than those of signals of DNA in companion runs conducted under comparable experimental conditions. The reduction of the intensity of the magnetic resonance signal paralleled the lowering of the intensity of the positive band above 260 nm in the circular dichroism spectrum of the given sample of chromatin relative to the spectrum of protein-free DNA. In fact, the percent reduction of the magnetic resonance signal of chromatin relative to protein-free DNA was, within experimental error, equal to the percentage of nucleotide residues in the Watson-Crick B secondary structure. Since the latter fraction of residues can be correlated with those in the interbead regions of the superstructure of chromatin, we have concluded that the signal of the nucleotide residues in the beads, or v bodies, has been broadened to the point of extinction by a packing arrangement which maximizes phosphate-protein interactions and structural rigidity.

Animals↗