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Biomedical subjects

L L Ng

Publications and source records attributed to L L Ng.

At least 91 records · Page 5Linked to original sources
PubMed1992

A comparison of four methods for assessing in vivo beta-cell function in normal, obese and non-insulin-dependent diabetic man.

Several methods of varying complexity are available for the measurement of in vivo insulin secretion in man. No study has previously compared these in the same subjects to establish which is the most appropriate for routine use. We have, therefore, compared four methods for measuring insulin secretion in man: Hyperglycaemic clamp (Hy), Minimal model (MIN), shortened intravenous glucose tolerance test (IVGTT) and continuous infusion of glucose with model assessment (C.I.G.M.A.). Seventeen subjects with varying degrees of insulin sensitivity were studied. Seven normal (BMI 22.5 +/- 1.5 kg/m2), five obese (BMI 38 +/- 5 kg/m2) and five NIDDM subjects (BMI 27 +/- 3 kg/m2) were investigated, in a randomised fashion, on separate days. First (PSI) and second phase (PSII) rate constants (MIN); incremental insulin secretion 0-10 mins (Hy delta I) and steady state insulin levels from the last 30 minutes (Hy120-150) from the hyperglycaemic clamp; 3 minute insulin concentration and incremental area under insulin secretion curve 0-10 min (IVGTT) and beta-cell function (%) from C.I.G.M.A. were used as indicators of insulin secretion. Each index of insulin secretion could detect an overall difference between the groups. Insulin secretion in normals and obese was similar but significantly increased compared to NIDDM. In normals PSI correlated with C.I.G.M.A. (Rs = 0.92, p < 0.02) and Hy120-150 (Rs = 0.82, p < 0.05). IVGTT0-10 correlated with PSII (Rs = 0.83, p < 0.05), HY delta I (Rs = 0.84, p < 0.05) and IVGTT3 min (Rs = 1.0, p < 0.001). In obese PSII correlated with C.I.G.M.A. (Rs = 0.91, p < 0.05), Hy delta I (Rs = 1.0, p < 0.02) Hy120-150 (Rs = 0.92, p < 0.05) and IVGTT3 min Rs = 1.0, p < 0.02). In addition Hy delta I also correlated with C.I.G.M.A. (Rs = 0.92, p < 0.05) and IVGTT3 min (Rs = 1.0, p < 0.02). In NIDDM Hy delta I correlated with C.I.G.M.A. (Rs = 0.91, p < 0.005). When all subjects from the three groups were combined, significant positive correlations were obtained between each index of insulin secretion. In conclusion we have demonstrated that: (a) C.I.G.M.A., IVGTT, Minimal model and hyperglycaemic clamp can provide similar overall results for, in vivo, beta-cell function in man. (b) Significant positive correlations were obtained between each index of insulin secretion when all subjects were combined. (c) Using the above methodologies insulin secretion in normal and obese appears similar but significantly increased compared to NIDDM subjects.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1992

Psychological aspects of rheumatic diseases.

Psychological problems in rheumatic diseases are common and influence the maintenance of symptoms and management. The psychological and psychosocial aspect of rheumatoid arthritis and systemic lupus erythematosus are briefly described. An approach to psychological management and the role of the psychiatrist in rheumatology are considered. In addition to appropriate and adequate treatment of concomitant psychological disorders with drugs, psychosocial interventions and the use of other forms of therapy such as self-help groups are also invaluable.

Arthritis, Rheumatoid↗
PubMed1991

Na+/H+ antiport and buffering capacity in human polymorphonuclear and mononuclear leucocytes.

1. Na+/H+ antiport activity was measured in peripheral blood polymorphonuclear and mononuclear cells of 12 healthy subjects by using an intracellular pH clamp technique to determine the external Na(+)-dependent H+ efflux rate in cells loaded with a pH-sensitive fluorescent dye, bis(carboxyethyl)carboxyfluorescein. The change in external Na+ concentrations for all pH measurements was similar in both cell types. 2. A significant difference between the two types of cells was found, the polymorphonuclear leucocytes having a higher Na+/H+ antiport activity than the lymphocytes. Cellular intrinsic buffering capacity measured in the absence of HCO3- was also higher in the polymorphonuclear cells than in the lymphocytes. 3. These differences may be associated with a difference in the role of the Na+/H+ exchanger in these two types of cells, although in vivo the presence of HCO3-/Cl- exchangers may also contribute to intracellular pH homoeostasis.

Adult↗
PubMed1991

Evidence for altered Na+/H+ antiport activity in cultured skeletal muscle cells and vascular smooth muscle cells from the spontaneously hypertensive rat.

1. Intracellular pH and Na+/H+ antiport activity were determined by a fluorimetric method in cultured skeletal muscle cells (myoblasts) and aortic vascular smooth muscle cells from spontaneously hypertensive and normotensive Wistar-Kyoto rats. 2. The intracellular pH was significantly more alkaline at three different extracellular pH values in both myoblasts and vascular smooth muscle cells from the spontaneously hypertensive rats than in those from the normotensive control rats. 3. A kinetic analysis of the Na+/H+ antiport activity in these cells showed that the raised activity in the spontaneously hypertensive rats was due to an increased maximal transport capacity in vascular smooth muscle cells and to an increase in the affinity of the antiport for internal H+ in the myoblasts. 4. When the extracellular pH was reduced in the skeletal muscle cells of both types of rat, the intracellular pH fell. However, in vascular smooth muscle cells, a reduction in the extracellular pH was not associated with a fall in the intracellular pH. This resistance of the intracellular pH to changes in the extracellular pH differentiates vascular smooth muscle cells from other cells that have been studied in this way.

Animals↗
PubMed1991

Intracellular free magnesium in human lymphocytes and the response to lectins.

1. Intracellular free [Mg2+] was measured in human peripheral blood lymphocytes using a fluorimetric method based on the dye furaptra. It was necessary to correct for the extracellular leakage of the dye by using either 10 mmol/l EDTA or 0.05 mmol/l Mn2+. 2. As the proliferative response of lymphocytes to mitogenic lectins has been linked to a dependence on extracellular Mg2+, the intracellular [Mg2+] was studied in lymphocytes stimulated with various mitogenic and non-mitogenic lectins. 3. Only lymphocytes treated with phytohaemagglutinin-L, a leucoagglutinin from Phaseolus vulgaris that binds to tri- and tetra-antennary complex glycoproteins, showed a marked increase in intracellular [Mg2+]. This effect was partially inhibited by N-acetylgalactosamine. The stimulation by different lectins of the incorporation of [3H]-thymidine into lymphocytes was not correlated to the changes in intracellular [Mg2+]. 4. The proliferative response of lymphocytes to lectins is therefore not wholly dependent on a rise in intracellular [Mg2+].

Benzofurans↗
PubMed1991

Effect of insulin on intracellular pH and phosphate metabolism in human skeletal muscle in vivo.

1. 31P nuclear magnetic resonance spectroscopy and the hyperinsulinaemic-euglycaemic clamp were used simultaneously to assess the effect of insulin on intracellular pH and the major phosphorus-containing metabolites of normal human skeletal muscle in vivo in four normal subjects. 2. Insulin and glucose were infused for 120 min. Plasma insulin increased approximately 10-fold over preclamp levels (5.6 +/- 0.9 m-units/l pre-clamp and 54 +/- 5 m-units/l over the last hour of infusion; mean +/- SEM, n = 4). Plasma glucose concentration did not change significantly (5.4 +/- 0.2 mmol/l pre-clamp and 5.5 +/- 0.1 mmol/l over the last hour of infusion). 3. Insulin and glucose infusion resulted in a decline in the intracellular pH of forearm muscle of 0.027 +/- 0.007 unit/h (P less than 0.01), whereas in control studies of the same subjects, pH rose by 0.046 +/- 0.005 unit/h (P less than 0.001). 4. In the clamp studies, intracellular inorganic phosphate concentration rose by 18%/h, whereas ATP, phosphocreatine and phosphomonoester concentrations did not change. In plasma, inorganic phosphate concentration was 1.16 +/- 0.05 mmol/l before infusion, and this decreased by a mean rate of 0.14 mmol h-1 l-1. No change was observed in any of these intracellular metabolites in the control studies. 5. The results show that, under physiological conditions, insulin does not raise intracellular pH in human muscle, and thus cannot influence muscle metabolism by this mechanism. The results also suggest that insulin causes a primary increase in the next flux of inorganic phosphate across the muscle cell membrane.

Adult↗
PubMed1991

Chloride influx in human leucocytes: a triple-isotope technique for the assessment of chloride transporters.

1. A novel triple-isotope method using 3H2O, [14C]-sucrose and 36Cl- for measuring initial Cl- uptake rates in human leucocytes that had been preincubated in 10% (v/v) autologous serum is described. 2. There was a marked dependence of Cl- influx on intracellular pH, the flux at an intracellular pH of 7.20 being about 11.2% of that at an intracellular pH of 7.56. 3. This Cl- influx was inhibited by 4,4-di-isothiocyanatostilbene-2,2-disulphonic acid in a dose-dependent manner. Half-maximal inhibition by 4,4-di-isothiocyanatostilbene-2,2-disulphonic acid at an internal pH of 7.56 in the presence or absence of HCO3- was 0.30 or 0.35 mmol/l, respectively. 4. Depletion of intracellular Cl- resulted in a 70.7% decrease in Cl- influx, whereas depletion of cellular ATP led to a 37.7% decrease in Cl- influx. 5. The phorbol ester 12-O-tetradecanoyl phorbol acetate at a concentration of 0.1 mumol/l reduced Cl-influx, especially the 4,4-di-isothiocyanatostilbene-2,2-disulphonic acid-sensitive component. This effect was independent of intracellular pH changes or Na+/H+ antiport activity.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1991

Leukocyte intracellular pH and Na/H antiporter activity in uraemia and type I diabetes mellitus.

The leukocyte Na/H antiporter has been studied in patients with end-stage renal failure on maintenance haemodialysis. Thirteen non-diabetic haemodialysis patients (CRF group) and eight haemodialysis patients with diabetic nephropathy (CRF-DM group) were investigated. Measurements were made using the pH-sensitive fluorescent dye bis (carboxyethyl) carboxyfluorescein (BCECF). The initial intracellular pH (pHi), intracellular buffering capacity, and Na/H antiporter Vmax (at pHi = 6.0) have been recorded in bicarbonate-free solutions. The mean initial intracellular pH in the CRF group was 7.34 (SD 0.05, P less than 0.004) and this was significantly less than the CRF-DM group (7.42, SD 0.07) and normal controls (7.43, SD 0.09, n = 25). The mean intracellular buffering capacity was normal in the CRF and CRF-DM groups. The mean Na/H antiporter Vmax was also normal in the CRF and CRF-DM groups (56.5, SD 9.9; and 56.8, SD 12.8, mmol/l per min respectively compared to 55.2, SD 8.8, mmol/l per min in controls). These data are discussed with reference to the reported high values of Na/H antiporter Vmax in diabetic patients with early nephropathy. This abnormality does not appear to be present in end-stage diabetic nephropathy.

Adolescent↗
PubMed1991

HMG CoA reductase inhibitors affect Na(+)-H+ antiport activity in human lymphoblasts.

The Na(+)-H+ antiport is a membrane-bound glycoprotein that extrudes intracellular acid loads and regulates cellular volume. Cellular synthesis of the oligosaccharide side chains of glycoproteins is dependent on a supply of mevalonate, itself a product of the rate-limiting enzyme of cholesterol synthesis 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase. The effect of two HMG CoA reductase inhibitors (simvastatin and 25-hydroxycholesterol) on intracellular pH and Na(+)-H+ exchange was therefore studied. Inhibition of the Na(+)-H+ antiport by these agents led to a fall in intracellular pH but did not impair the regulatory volume increase response to a hypertonic stimulus. The inhibitory effect of simvastatin was prevented by mevalonate but not dolichol or squalene. The effect of 25-hydroxycholesterol was more complex and not easily reversed. Thus HMG CoA reductase inhibitors reduced the ability of human lymphoblasts to expel an intracellular acid load via the Na(+)-H+ antiport, although the response of the antiport to an osmotic stimulus was preserved.

Blastomeres↗
PubMed1991

Modulation of Na-H antiporter activity in human lymphoblasts by altered membrane cholesterol.

The effects of changes in membrane cholesterol on Na-H antiporter activity in culture human lymphoblasts are described. Lymphoblast cholesterol alteration was achieved with liposomes of phosphatidylcholine (cholesterol depletion) or phosphatidylcholine plus cholesterol (cholesterol enrichment). Lymphoblast intracellular pH (pHi) was examined by fluorimetry using cells loaded with the pH-sensitive dye 2',7'-bis(2-carboxyethyl)5(6)-carboxyfluorescein, and the Na-dependent proton efflux rate at a pHi of 6.0 was taken as the maximum velocity of the Na-H antiporter. Lymphoblast membrane cholesterol depletion activated the Na-H antiporter, and enrichment of membrane cholesterol caused inhibition of the antiporter activity. This study demonstrates that in situ modification of membrane cholesterol can modulate the activity of the Na-H antiporter.

Carrier Proteins↗
PubMed1991

Stimulation of the human leucocyte Na+/H+ antiport by D-glucose is mediated by protein kinase C.

Leucocyte Na+/H+ antiport activity is elevated in patients with essential hypertension and Type 1 diabetes with nephropathy. To examine the effects of hyperglycemia on the Na+/H+ antiport, normal leucocytes were incubated with 25 mmol l-1 D-glucose, L-glucose or glucose-6-phosphate for two days. Leucocyte Na+/H+ antiport activity was measured by a novel double ionophore fluorimetric method for controlling intracellular pH. Only incubation with D-glucose led to an increase in Na+/H+ antiport activity of about 31%. This effect was not due to non-enzymic glycation since glucose-6-phosphate, which glycates proteins faster than D-glucose, caused no significant difference in antiport activity. Also, osmotic effects could be excluded. Staurosporine (10 nmol l-1), a specific inhibitor of protein kinase C, prevented the rise in antiport activity due to incubation with D-glucose. As hyperglycaemia is known to increase protein kinase C activity, elevation of this kinase may be one mechanism for activation of the Na+/H+ antiport in Type 1 diabetes.

Adult↗
PubMed1991

Psychiatric problems in the elderly.

Psychosocial changes and physical disabilities that occur in the elderly contribute to an increase in the prevalence of psychiatric disorders in the elderly. A comprehensive approach to diagnosis is required. Depression, dementia, delirium and paranoid disorders are common psychiatric disorders seen in the elderly. Underlying treatable causes must be excluded. Treatment requires special considerations such as adverse drug reactions, drug interactions, side effects and concomitant physical illnesses. Management of the elderly should involve the family as well as the patient.

Aged↗
PubMed1990

Effect of protein kinase C modulators on the leucocyte Na+/H+ antiport in type 1 (insulin-dependent) diabetic subjects with albuminuria.

It is uncertain why only one third of Type 1 (insulin-dependent) diabetic patients develop nephropathy. One suggestion is the inheritance of a predisposition to essential hypertension. We have previously found elevated Na+/H+ antiport activity and a raised intracellular pH in leucocytes from hypertensive and Type 1 diabetic subjects with albuminuria using a novel double ionophore fluorimetric technique. These changes are not found in Type 1 diabetic subjects without albuminuria. We wished to test the effect of a protein kinase C inhibitor staurosporine (100 nmol/l) on the elevated antiport activity, and the degree of stimulation achieved by exogenous diacyl glycerol. Raised leucocyte Na+/H+ antiport activity of Type 1 diabetic subjects with albuminuria (73.8 +/- 17.2 mmol.l-1.min-1) was restored to normal levels with staurosporine (54.9 +/- 17.9 mmol.l-1.min-1, p less than 0.001). The leucocyte Na+/H+ antiport activity of diabetic subjects without albuminuria fell significantly also with staurosporine but to a lesser extent (57.3 +/- 11.6 to 50.0 +/- 12.8 mmol/l, p less than 0.003). In contrast, leucocytes from normal control subjects showed no change in antiport activity with staurosporine (54.3 +/- 8.5 to 52.6 +/- 10.4 mmol.l-1.min-1). Dioctanoyl glycerol stimulated the leucocyte Na+/H+ antiport in normal subjects and diabetic patients without albuminuria, with significantly less stimulation in diabetic patients with albuminuria. We conclude that reversal by staurosporine of the elevated Na+/H+ antiport activity in Type 1 diabetic subjects with albuminuria could indicate a role for protein kinase C in activating the antiport. This hypothesis is supported by the reduced stimulation of the antiport by dioctanoyl glycerol in this group of patients.

Albuminuria↗
PubMed1990

Leucocyte Na+/H+ antiport activity in type 1 (insulin-dependent) diabetic patients with nephropathy.

The development of proteinuria in Type 1 (insulin-dependent) diabetic patients may depend on predisposition to essential hypertension in addition to poor glycaemic control. Previous work has shown increased leucocyte Na+/H+ antiport activity in essential hypertension and increased erythrocyte Li+/Na+ exchange in Type 1 diabetic patients with proteinuria. To test whether susceptibility to nephropathy in Type 1 diabetes was linked to abnormalities of leucocyte Na+/H+ antiport activity, we measured the intracellular pH and kinetics of the Na+/H+ antiport in 19 Type 1 diabetic subjects with, and 15 diabetic subjects without albuminuria and compared them to 25 matched normal control subjects. Intracellular pH (mean +/- SD 7.59 +/- 0.14) and maximal transport capacity of the antiport (Vmax 87.7 +/- 24.9 mmol.1-1.min-1) were higher in diabetic subjects with albuminuria compared to normotensive control subjects (pH 7.44 +/- 0.09; Vmax 55.6 +/- 10.3 mmol.l-1.min-1; p less than 0.001 for both), similar to the defect described in essential hypertension. These differences were not seen in diabetic subjects with normal urinary albumin/creatinine ratios (pH 7.46 +/- 0.09; Vmax 61.0 +/- 13.6 mmol.l-1.min-1). Buffering characteristics of the leucocytes at different pH in the Type 1 diabetic subjects with albuminuria differed from normal control subjects and diabetic subjects with normal urinary albumin/creatinine ratios. We conclude that increased leucocyte Na+/H+ antiport activity, a known marker of essential hypertension, is usually associated with nephropathy in Type 1 diabetes.

Albuminuria↗
PubMed1990

Leukocyte isotopically exchangeable intracellular sodium fractions in lean and overweight hypertensives.

Leukocyte intracellular sodium, as measured by flame photometry, is increased in essential hypertension, especially when associated with a body mass index greater than 27 kg.m-2. A triple isotope method for measuring the isotopically exchangeable pool of intracellular sodium was used to assess if this pool was increased in hypertension. No significant differences in the isotopically exchangeable intracellular sodium concentration were found between lean and overweight hypertensives compared with normotensive controls. Lean hypertensives with systolic blood pressures below the median had significantly lower exchangeable intracellular sodium concentrations than lean normotensives, whereas those with systolic blood pressures above the median had raised exchangeable intracellular sodium concentrations. The obese hypertensives did not show this trend. The exchangeable intracellular sodium concentration was correlated to systolic (r = .53, P less than .001) and diastolic (r = 0.39, P less than .01) blood pressure in hypertensives. We conclude that the increase in total cellular sodium content (as measured by flame photometry) in hypertensives described in previous studies is not associated with any increase in the isotopically exchangeable pool of intracellular Na+, except in those lean hypertensives with systolic blood pressures above the median. By implication, there may be an increased slowly exchangeable pool of intracellular Na+ in leukocytes from most hypertensives.

Adult↗
PubMed1990

myo-inositol influx into human leucocytes: methods of measurement and the effect of glucose.

1. Low intracellular concentrations of myo-inositol in diabetic cells may contribute to the development of tissue damage. The cause of these low levels is unknown, but inhibition of a putative myo-inositol transporter by high concentrations of glucose has been proposed. We have developed a triple-isotope method for estimating myo-inositol influx into human leucocytes and so investigated both the kinetics of this uptake in normal volunteers and the effect of glucose upon it. 2. Uptake was composed of a passive component with a rate constant of 2.4 +/- 0.3 X 10(-2) min-1 and a saturable component with a Km of 61 +/- 23 mumol/l and Vmax of 11.3 +/- 4.5 X 10(-4) mmol min-1 l-1. Ouabain and low extracellular concentrations of sodium partly inhibited influx. Uptake was predominantly into the cytosolic fraction of the cell with 12% entering the membrane-associated fraction at both 5 and 10 min. 3. myo-Inositol influx was significantly inhibited by both D- and L-glucose but not by sucrose. Neither cytochalasin B nor ethyl isopropyl amiloride significantly inhibited uptake. 4. It is concluded that a myo-inositol transporter exists in human leucocytes which is similar to that found in other species and tissues. Our technique allows myo-inositol influx in diabetic subjects to be related to varying glycaemic control and tissue damage.

Adult↗