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Biomedical subjects

K S Tan

Publications and source records attributed to K S Tan.

At least 55 records · Page 3Linked to original sources
PubMed1991

Cell lines of novel type derived from a diabetic secrete tissue-reactive human monoclonal antibodies.

Human monoclonal antibodies have been produced from lymphocytes of an acute-onset insulin-dependent diabetic patient. Peripheral blood lymphocytes were hybridized with a fusion partner HMY-1320. Initial screening of human immunoglobulin secretion was made by a nitrocellulose dot blot assay. Ten stable cell lines of novel type, secreting human immunoglobulin, were obtained. These cell lines have been maintained in continuous culture over 6 months and cryopreserved in liquid nitrogen for 14 months. Human monoclonal antibodies of IgG and IgM class have been produced and are secreted at a rate of 150-650 ng/ml/10(6) cells/day. Monoclonal antibodies were tested for histological staining against a variety of endocrine and non-endocrine tissues. One monoclonal antibody, LT1E12, demonstrates a staining pattern in human, rat, and mouse tissues, similar to that of mitochondrial antibodies. Another antibody, LT3C4, demonstrates weak staining of smooth muscle in rat and mouse kidney sections. Neither specificities were detected in the diabetic patient's serum. The variety of immune tissue specificities obtained in this study demonstrates the potential value of human monoclonal antibodies as probes to analyze the complexity of autoimmunity in diabetes mellitus.

Antibodies, Monoclonal↗
PubMed1991

Training and assessment of observers for blood pressure measurement in hypertension research.

Eight nurses were re-trained in the technique of measuring blood pressure firstly with an audiotape and secondly with a video and expert instruction. They were then assessed for accuracy in measurement in subjects with a range of BP. In the first session with the audiotape, criteria for accuracy were that the difference in readings (systolic and diastolic) between each pair of observers was to be 5 mm Hg or less in at least 85% and 10 mm Hg or less in at least 95% of the readings. Five out of the 28 observer pairs (18%) fulfilled these criteria for both systolic and diastolic pressures, six (21%) satisfied the criteria for systolic pressure and nine (32%) for diastolic pressure with eighteen pairs (64%) failing to meet the criteria for both systolic and diastolic pressure. In the second training session seven of the original eight observers underwent further training in which the audio-tape was replaced by the British Hypertension Society video and instruction was also given by an expert. The same requirements for accuracy were used except that, in addition, the difference between the trainee observer and the expert had to be within 5 mm Hg in at least 90% and within 10 mm Hg in at least 95% of the readings. Eighteen of the 21 observer pairs (86%) achieved the accuracy criteria, with the remaining three (14%) failing on diastolic pressure only. All seven observers were within the required criteria when assessed against the expert observer. It is concluded that training of observers is more effective with a video and expert instruction than by using audio-tapes.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Pressure Determination↗
PubMed1987

Human monoclonal antibodies to thyroid antigens derived by hybridization of lymphocytes from a diabetic patient.

Human monoclonal antibodies to human endocrine cells have been obtained following the generation of immunoglobulin-secreting interspecies lymphocyte hybridomas. Peripheral blood lymphocytes from an adult patient presenting with acute onset, Type I, diabetes mellitus were fused in vitro with mouse myeloma cells of the NS1 cell line. Initial selection of resulting hybridomas was made by their ability to proliferate in HAT medium. Those hybridomas secreting human immunoglobulins were identified by radioimmunoassay and, thereafter, cloned at frequent intervals to ensure continued antibody production. Human monoclonal antibodies selected in this manner are being employed to identify those epitopes which are common antigenic targets during initial stages of autoimmune-mediated diabetes mellitus and associated multiple endocrinopathies. Of these antibodies, one (HML 3.22) recognizes an epitope present on the human TSH receptor and a second (HML 3.21) identifies a component of thyroglobulin. The potential value of human monoclonal antibodies as probes for analyzing autoimmune-mediated endocrine diseases is discussed.

Animals↗
PubMed1987

Metabolic effects and secretory properties of a radiation-induced transplantable rat insulinoma.

The metabolic effects and secretory properties of a radiation-induced transplantable insulinoma were examined in 16-17 week old NEDH rats. Subcutaneous subscapular implantation of tumour fragments resulted in hyperphagia, increased body weight gain, marked hyperinsulinaemia and severe hypoglycaemia, with the resulting death of the recipient by 27 days. Ultimate tumour size was 2.1 +/- 0.4 g (mean +/- SEM). At 3 days after transplantation, plasma glucose and insulin responses to intraperitoneal glucose, insulin, arginine and adrenaline were similar to control rats. At 20 days, plasma glucose concentrations of insulinoma-bearing rats remained low throughout glucose tolerance tests, and insulin responsiveness to glucose stimulation was absent. 2-Deoxy-D-glucose produced only a small rise of glucose concentrations in tumour-bearing rats. Insulin sensitivity was not appreciably impaired at 20 days despite severe hyperinsulinaemia and hypoglycaemia. The ability of adrenaline and propranolol to suppress plasma insulin and raise plasma glucose concentrations was also retained. At 20 days, glucagon evoked a marked plasma insulin response with no change in plasma glucose concentrations. In contrast, arginine and glibenclamide failed to stimulate insulin above high basal concentrations.

Adenoma, Islet Cell↗
PubMed1987

Effects of cytotoxic drugs and inhibitors of insulin secretion on a serially transplantable rat insulinoma and cultured rat insulinoma cells.

The effects of cytotoxic drugs and inhibitors of insulin secretion were examined in vivo in rats with a radiation-induced transplantable insulinoma, and in vitro using cultured rat insulinoma cells and the derived RINm5F insulin-secreting cell line. Administration of diazoxide to insulinoma-bearing rats resulted in a transient decrease of plasma insulin with a temporary rise of glucose concentrations. Mannoheptulose and somatostatin failed to affect the marked hyperinsulinaemia and hypoglycaemia. Streptozotocin produced a rapid and sustained decrease of insulin concentrations in insulinoma-bearing rats, accompanied by a progressive elevation of plasma glucose. Administration of alloxan failed to affect circulating insulin or glucose concentrations. In vitro, streptozotocin and alloxan exerted approximately equipotent time-dependent and concentration-dependent cytotoxic effects on insulinoma cells and RINm5F cells as established by cell staining with trypan blue. The cytotoxic actions of both drugs were decreased by agents believed to scavenge free radicals or to act as inhibitors of poly(ADP-ribose) synthetase. The results suggest that the cytotoxic actions of streptozotocin and alloxan on rat insulinoma cells and RINm5F cells are mediated by the generation of hydroxyl free radicals and DNA strand breaks. The ineffectiveness of alloxan in insulinoma-bearing rats probably reflects the high rate of decomposition of the drug in vivo.

Adenoma, Islet Cell↗
PubMed1987

Defective diurnal changes of food intake, plasma glucose and insulin in rats with a transplantable islet cell tumour.

Subcutaneous implantation of small fragments of a radiation-induced transplantable rat insulinoma into the subscapular region of 16- to 17-week-old male NEDH rats resulted, over a 22-day period, in the progressive development of marked hyperinsulinaemia and severe hypoglycaemia, despite a compensatory increase in food intake. Diurnal changes were examined at 3-hourly intervals for 24 h in control rats and tumour-bearing rats at 20-21 days after transplantation. The control animals exhibited distinct diurnal changes of food intake, glucose and insulin concentrations. Food intake was greatest between 17.00 and 23.00 h; plasma insulin was greatest between 20.00 and 23.00 h, and plasma glucose was raised at 20.00, 02.00 and 05.00 h, compared with the other times. In contrast, insulinoma-bearing rats displayed no diurnal changes other than a small decrease in food intake between 05.00 and 11.00 h. Plasma glucose and insulin concentrations were significantly different from control rats at all times, and food intake was significantly increased between 23.00 and 17.00 h. These observations demonstrate that the transplantable insulinoma not only causes hyperinsulinaemia and hypoglycaemia but results in hyperphagia and defective diurnal changes of food intake, plasma glucose and insulin concentrations. Interruption of nutrient intake by withdrawal of food for 6 h exacerbated the hypoglycaemia of insulinoma-bearing rats leading to coma.

Adenoma, Islet Cell↗
PubMed1986

Differential insulin responses to oral and intravenous glucose in the transplantable rat insulinoma--a role for GIP.

We have previously demonstrated an impaired insulin response to intraperitoneal glucose and arginine by the transplantable NEDH rat insulinoma. The nature of this tumour B-cell defect has been further studied by investigating the response of insulinoma-bearing rats to intravenous and intragastric glucose. Intravenous glucose failed to stimulate plasma immunoreactive insulin (IRI) above high basal levels (14.5 +/- 1.1 micrograms/L). However, significant elevation of the plasma IRI concentration was observed following an intragastric glucose load (17.1 +/- 1.5 micrograms/L; P less than 0.02). In view of the different effects of oral and intravenous glucose on insulin secretion in the RIN, implicating an involvement of incretin factors from the gut, the response of the tumour to GIP was investigated. Plasma IRI concentrations rose significantly in these animals (20.6 +/- 2.5 micrograms/L at 5 min, P less than 0.02). We conclude that (a) the transplantable rat insulinoma is responsive to GIP, and (b) that whilst the tumour B-cell has lost its insulin responsiveness to hyperglycaemia produced by intraperitoneal or intravenous glucose, it retains its ability to respond to intragastric glucose. This could be due to incretin factors from the gut of which GIP is currently the strongest candidate.

Adenoma, Islet Cell↗
PubMed1986

Effects of transplantation and resection of a radiation-induced rat insulinoma on glucose homeostasis and the endocrine pancreas.

Twenty-one days after s.c. subscapular transplantation of a radiation-induced insulinoma, male NEDH rats exhibited hyperinsulinaemia and hypoglycaemia. These features were associated with islet atrophy, degenerative changes in pancreatic A and B cells, and decreases in the pancreatic contents of insulin, glucagon and somatostatin. The immunoreactive glucagon and somatostatin contents of extrapancreatic tissues of insulinoma-bearing rats were unchanged. Surgical resection of the tumour resulted in an immediate fall of plasma insulin, attaining concentrations similar to those of anaesthetised control rats by 10 min. The estimated half-life of insulin was 3.5 min. Hypoglycaemia persisted until 60 min after resection, followed by hyperglycaemia of 1-2 days duration. Glucose tolerance was impaired 1 day after tumour resection despite the coexistence of raised insulin concentrations. Evidence for abnormal pancreatic B cell function was gained by injection of arginine which failed to evoke a plasma insulin response in the resected rats. Two days after resection, plasma glucose and insulin concentrations were similar to those of control rats. Plasma glucose and insulin responses to glucose and arginine were suggestive of tumour recurrence by 12 days. A single large encapsulated tumour was eventually observed in each rat, with resection giving a 17-56 day prolongation of life.

Adenoma, Islet Cell↗
PubMed1985

Benzodiazepines produce contrasting effects on the active membrane properties of an invertebrate neuron.

A perturbation of excitable membranes mediated by non-receptor (non-specific) mechanisms might be predicted from the hydrophobic nature of 1,4-benzodiazepines. Since correlations between membrane properties and neuronal effects have not been described for benzodiazepines, the effects of flurazepam, oxazepam and the benzodiazepine antagonist flumazepil (Ro 15-1788) were examined on both passive and active electrical properties of the membrane and neuronal discharge frequency. In this study, the isolated sensory neuron of the crayfish has been utilized as a neuronal model system. Flurazepam and flumazepil both enhanced the discharge frequency, in contrast to the depression produced by oxazepam. Discharge frequency was directly correlated with the maximum rate of rise of membrane potential during the threshold phase and was inversely correlated with spike threshold. In addition, the discharge frequency appeared to exhibit little dependence on peak amplitude, duration and the maximum rate of depolarization of the action potential. These findings are discussed in relation to non-specific mechanism(s) of action for benzodiazepines. It is suggested that, in the absence of a specific drug-receptor interaction, benzodiazepines in larger concentrations (greater than or equal to 50 mumol/l) exhibit selective membrane perturbations.

Action Potentials↗
PubMed1984

Synaptic and non-synaptic actions of benzodiazepines on the crayfish sensory neuron.

On the stretch-induced discharge activity of the isolated crayfish sensory neuron flurazepam (less than or equal to 3 X 10(-4) M) and Ro 15-1788 (less than or equal to 10(-3) M) produced reversible concentration-dependent excitation, but oxazepam only produced depression (less than or equal to 5 X 10(-4) M). Similar divergent effects on the membrane properties were observed. Oxazepam increased the threshold to firing without changing resting potential, membrane resistance or the GABA-mediated IPSP. In contrast flurazepam and Ro 15-1788 produced a concentration-dependent decrease in threshold. Flurazepam did not alter membrane resistance or resting potential but facilitated GABA transmission. Ro 15-1788 had the opposite effect on the GABA synapse, and also depolarized the resting potential but did not alter membrane resistance. The change in spike threshold appeared to be an important component in producing discharge excitation or depression. These results not only demonstrate the capability of the sensory neuron to discriminate between structures of benzodiazepines, but also that these agents can produce divergent effects on synaptic and non-synaptic properties of a single neuron.

Action Potentials↗
PubMed1984

Evidence for excitatory and depressant non-receptor-mediated membrane effects of benzodiazepines in the crayfish.

Oxazepam produced a significant reversible monophasic concentration-dependent (50-500 mumol/l) depression of stretch-induced discharge frequency of the isolated crayfish sensory neuron. In total contrast, flurazepam (10-200 mumol/l) evoked reversible excitation of the neuronal firing rate but at concentrations greater than 300 mumol/l it induced transient excitation followed by secondary total depression. The benzodiazepine antagonist flumazepil (less than or equal to 1 mmol/l) also produced an inherent increase in neuronal discharge frequency, though respective concentrations of 50 and 100 mumol/l failed to block flurazepam-excitation or oxazepam-depression. It is suggested that these high concentration qualitatively divergent neuronal effects are not mediated through specific benzodiazepine receptors.

Animals↗
PubMed1984

An in vitro study of copper and copper chelators on the crayfish stretch receptor.

This study demonstrates the effects of micromolar concentrations of copper on the discharge firing activity of the isolated crayfish stretch receptor. Different pharmacological profiles of action were obtained with the divalent (cupric) and monovalent (cuprous) salt solutions. Cupric solutions produced a concentration-dependent triphasic effect (depression-excitation-depression); in contrast, a monophasic effect (depression) was produced by cuprous solutions. The effectiveness of copper chelators, in reversing these effects, were compared with normal physiological solution. Only the first phase of the effects of cupric were partially reversed with physiological solution or ethylenediamine tetraammonium (EDTA). In the presence of D-penicillamine and triethylene tetramine (trien), all phases of the effects of both cuprous and cupric salts were completely restored to control values. In addition, copper was shown to be the most neurotoxic divalent cation examined. The results demonstrate that effects of copper on neuronal activity are dependent on time, concentration and valency state.

Animals↗
PubMed1982

Experimental production of complete heart block by electrocoagulation in the closed chest dog.

Methods for producing complete heart block in experimental animals have usually required thoracotomy to gain access to the intracardiac conduction system. A closed chest technique has been developed for producing discrete permanent lesions in the atrioventricular node or His bundle of anesthetized dogs. An insulated transseptal needle is passed through a venous catheter to the right atrium. The exposed tip is pressed into the His bundle and a 30 to 40 joule pulse from a DC defibrillator is transmitted through the needle. This produces a 1 to 3 mm diameter coagulative lesion which permanently destroys the tissue at this point. The process can be repeated until complete heart block is achieved. Our procedure has been successful in 45 of 46 attempts to prepare dogs for acute experiments and, using implanted pacemakers, for chronic studies. We conclude that this closed chest method is a safe and reliable alternative for production of complete heart block requiring thoracotomy, thereby providing an important new means for both acute and chronic experimental studies requiring complete heart block for the improved elucidation of mechanisms and management of cardiovascular diseases.

Animals↗
PubMed1981

A simple and sensitive force transducer suitable for measuring tensions in small muscle fibers.

The design and fabrication of a simple tension force transducer, sensitive enough to measure tensions of individual and fine bundles of muscle fibers, is described. The transducer is capable of accurately measuring tensions as little as 0.5 dynes along the longitudinal axis of fibers. The response of the transducer is linear within the range of 0.5 to 500 dynes. Examples of its use and small crustacean striated and vertebrate cardiac muscle fibers are presented.

Animals↗