Search PubMed⌕ Search

Biomedical subjects

I A Simpson

Publications and source records attributed to I A Simpson.

At least 127 records · Page 7Linked to original sources
PubMed1986

Insulin stimulates glucose transport in isolated human adipose cells through a translocation of intracellular glucose transporters to the plasma membrane: a preliminary report.

Insulin's effect on glucose transport activity and the subcellular distribution of glucose transporters have been examined in isolated human abdominal adipose cells, by measuring 3-O-methylglucose transport and specific D-glucose-inhibitable cytochalasin B binding to plasma membranes and low-density microsomes, respectively. Insulin appears to stimulate glucose transport in isolated human adipose cell through the translocation of glucose transporters from a large intracellular pool to the plasma membrane as initially postulated for rat adipose and muscle cells.

Adipose Tissue↗
PubMed1986

Comparison of Doppler ultrasound velocity measurements with pressure differences across bioprosthetic valves in a pulsatile flow model.

Continuous wave Doppler ultrasound was used in vitro to assess the pressure differences across four different cardiac bioprosthetic valves in a pulsatile flow test apparatus. Valves were tested under four different flow conditions. Pressure differences were calculated from the maximum flow velocity measured by Doppler ultrasound and correlated well with the pressure differences measured directly in the flow model (r = 0.98). Thus Doppler ultrasound can accurately measure pressure differences across bioprosthetic valves in vitro.

Bioprosthesis↗
PubMed1986

Ultrafiltration in the management of refractory congestive heart failure.

Ultrafiltration was performed in nine patients with congestive cardiac failure that was refractory to conventional medical treatment. A mean of 12 X 7 litres of fluid was removed, and there was a sustained symptomatic improvement in all patients. Weight loss continued after ultrafiltration and a sustained increase in serum sodium concentration was also noted. A transient fall in right atrial pressure was seen only at four hours after ultrafiltration. No adverse haemodynamic effects were seen four and eighteen hours after fluid removal. Intracardiac dimensions measured by echocardiography remained unchanged. Ultrafiltration can be used to relieve symptoms in patients with refractory congestive heart failure and gross oedema.

Blood Pressure↗
PubMed1986

Doppler ultrasound in the estimation of the severity of pulmonary infundibular stenosis in infants and children.

Pressure gradients estimated by Doppler echocardiography were compared with values obtained at cardiac catheterisation in 31 children (aged seven days to 16 years, mean 2 years 7 months) with pulmonary infundibular stenosis including 16 with tetralogy of Fallot. Various parasternal and subcostal positions were explored to obtain the maximum velocity of blood flow and the obstructive gradient was calculated from the modified Bernoulli formula. The gradient across the obstruction could be measured directly at the time of catheterisation in only 21 patients. The correlation coefficient for the Doppler and total measured gradients was r = 0.90 for catheter entry and r = 0.77 for catheter withdrawal. Doppler ultrasound, by measuring the total gradient from the right ventricle to the pulmonary artery, provides a non-invasive assessment of the severity of pulmonary stenosis, and in those with infundibular obstruction allowance need not be made for possible energy losses caused by the elongated obstruction or the presence of narrowing at more than one level.

Adolescent↗
PubMed1986

Non-invasive assessment by Doppler ultrasound of 155 patients with bioprosthetic valves: a comparison of the Wessex porcine, low profile Ionescu-Shiley, and Hancock pericardial bioprostheses.

One hundred and fifty five patients with 167 bioprosthetic valves (68 Wessex porcine, 54 Hancock pericardial, and 45 low profile Ionescu-Shiley pericardial valves) were studied by Doppler ultrasound. Valve gradients were calculated from the mitral and aortic flow velocities by the modified Bernoulli equation. Mean mitral gradients were significantly smaller across the Ionescu-Shiley valves than across the Wessex porcine or Hancock pericardial valves. Mitral pressure half time was, however, significantly longer in the Hancock pericardial than in the Wessex porcine or Ionescu-Shiley valves. No significant differences were seen among the groups of aortic bioprostheses, though the comparable size of Wessex porcine valves showed significantly higher gradients. Bioprosthetic regurgitation was detected in 13 of 103 mitral and 11 of 59 aortic valves, though it was suspected clinically in only 12 mitral and six aortic bioprostheses. Doppler ultrasound is a repeatable non-invasive method of acquiring haemodynamic information in vivo from a variety of bioprostheses and it can detect bioprosthetic regurgitation at an early stage.

Adult↗
PubMed1986

An unusual presentation of variant angina.

A previously well 46-year-old man presented with ventricular fibrillation as an initial complication of Prinzmetals variant angina. Coronary angiography subsequently demonstrated normal coronary arteries.

Angina Pectoris, Variant↗
PubMed1985

Biosynthesis of the insulin receptor in rat adipose cells. Intracellular processing of the Mr-190 000 pro-receptor.

We investigated the biosynthesis of the insulin receptor in primary cultures of isolated rat adipose cells. Cells were pulse-chase-labelled with [3H]mannose, and at intervals samples were homogenized. Three subcellular membrane fractions were prepared by differential centrifugation: high-density microsomal (endoplasmic-reticulum-enriched), low-density microsomal (Golgi-enriched), and plasma membranes. After detergent solubilization, the insulin receptors were immunoprecipitated with anti-receptor antibodies and analysed by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis and autoradiography. After a 30 min pulse-label [3H]mannose first appeared in a band of Mr 190 000. More than 80% of the Mr-190 000 component was recovered in the microsomal fractions. Its intensity reached a maximum at 1 h in the high-density microsomal fraction and at 2 h in the low-density microsomal fraction, and thereafter declined rapidly (t 1/2 approx. 3 h) in both fractions. In the plasma-membrane fraction, the radioactivity in the major receptor subunits, of Mr 135 000 (alpha) and 95 000 (beta), rose steadily during the chase and reached a maximum at 6 h. The Mr-190 000 precursor could also be detected in the high-density microsomal fraction by affinity cross-linking to 125I-insulin. In the presence of monensin, a cationic ionophore that interferes with intracellular transport within the Golgi complex, the processing of the Mr-190 000 precursor into the alpha and beta subunits was completely inhibited. Our results suggest that the Mr-190 000 pro-receptor originates in the endoplasmic reticulum and is subsequently transferred to the Golgi complex. Maturation of the pro-receptor does not seem to be necessary for the expression of the insulin-binding site. Processing of the precursor into the mature receptor subunits appears to occur during the transfer of the pro-receptor from the Golgi complex to the plasma membrane.

Acetylglucosaminidase↗
PubMed1985

Effect of Ciprofibrate on platelet aggregation and fibrinolysis in patients with hypercholesterolaemia.

The fibrinolytic and platelet effects of Ciprofibrate, a new lipid lowering drug, were studied in 7 patients with hypercholesterolaemia over a 12 week period. A significant reduction in plasma fibrinogen was noted and a lesser increase in fibrinolytic activity. However, no change in platelet aggregation was noted. As expected Ciprofibrate produced a significant hypolipidaemic effect in these patients. We have described effects of Ciprofibrate which may have potential benefits in this high risk patient group.

Adult↗
PubMed1985

The severity of pulmonary valve or artery obstruction in children estimated by Doppler ultrasound.

Doppler echocardiographic estimation of pressure gradient has been compared to that measured at cardiac catheterisation in 37 children, 6 weeks to 15 years of age, with suspected pulmonary valve stenosis or a pulmonary artery band. Various parasternal and subcostal positions were explored to obtain the maximum velocity of blood flow and the valve gradient was calculated from the modified Bernoulli formula. The Doppler study was performed at the time of catheterisation in 19, the maximum velocity being measured during catheter withdrawal in 7, immediately after withdrawal in 7, and while simultaneous right ventricular and pulmonary arterial pressures were measured in 5. Five other patients were studied within 24 hours of catheterisation and the other 13 within 6 months. Comparison of Doppler and catheterisation gradients showed a close correlation, this being particularly good where simultaneous right ventricular and pulmonary arterial pressures were measured. Doppler now provides an accurate non-invasive measurement of the severity of pulmonary valve stenosis and the adequacy of a pulmonary artery band.

Adolescent↗
PubMed1985

Clinical value of Doppler echocardiography in the assessment of adults with aortic stenosis.

Continuous wave Doppler echocardiography was used to study 41 adults with clinically suspected aortic stenosis undergoing cardiac catheterisation. Non-invasive assessment of the severity of stenosis was made before catheterisation using electrocardiograms, chest radiographs, and cross sectional echocardiography in addition to clinical examination and assessment modified, where appropriate, by the result of the Doppler examination. Catheterisation gradients were obtained in 33 patients and correlated well with those obtained by Doppler examination particularly when simultaneous recordings were obtained. All patients with surgically significant stenoses were identified by non-invasive assessment including Doppler examination and overestimation was not found in any patient with a less than significant stenosis. Thus surgery can be recommended in patients with aortic stenosis without the need for previous cardiac catheterisation.

Adolescent↗
PubMed1985

Integral membrane protein translocations in the mechanism of insulin action.

The subcellular distributions of insulin and insulin-like growth factor type II (IGF-II) receptors, and glucose transporters, have been examined in basal and insulin-stimulated rat adipose cells. Plasma membranes (PM), high-density microsomes (HDM) and low-density microsomes (LDM) were prepared by differential ultracentrifugation. Insulin receptors were quantified by 125I-insulin binding or lactoperoxidase 125I-iodination and immunoprecipitation, IGF-II receptors by 125I-IGF-II binding, and glucose transporters by specific D-glucose-inhibitable [3H]cytochalasin B binding. In the basal state, more than 90% of the cells' insulin receptors are localized to PM, and approximately 90% of the cells' glucose transporters and IGF-II receptors are associated with LDM. In the maximally insulin-stimulated state, the number of insulin receptors in PM is decreased by approximately 30%, of which approximately half are recovered in LDM and the remainder in HDM in an inverted configuration. Concomitantly, the numbers of glucose transporters and IGF-II receptors in LDM are decreased by approximately 60% and approximately 22%, respectively, with stoichiometric numbers appearing in PM. All three redistribution processes are rapid (t1(2) = 2-3 min), achieving new steady states in 5-10 min. The redistributions of glucose transporters and IGF-II receptors are half-maximal at approximately 0.1 nM-insulin, whereas insulin receptor redistribution correlates with receptor occupancy (1/2max approximately equal to 3 nM). Thus, insulin stimulates the rapid and simultaneous subcellular translocations of its own receptors and, in the opposite direction, IGF-II receptors and glucose transporters.

Adipose Tissue↗
PubMed1984

Internalization of insulin receptors in the isolated rat adipose cell. Demonstration of the vectorial disposition of receptor subunits.

The internalization of the insulin receptor in the isolated rat adipose cell and the spatial orientation of the alpha (Mr = 135,000) and beta (Mr = 95,000) subunits of the receptor in the plasma membrane have been examined. The receptor subunits were labeled by lactoperoxidase/Na125I iodination, a technique which side-specifically labels membrane proteins in intact cells and impermeable membrane vesicles. Internalization was induced by incubating cells for 30 min at 37 degrees C in the presence of saturating insulin. Plasma, high density microsomal (endoplasmic reticulum-enriched), and low density microsomal (Golgi-enriched) membrane fractions were prepared by differential ultracentrifugation. Receptor subunit iodination was analyzed by immunoprecipitation with anti-receptor antibodies, sodium dodecyl sulfate/polyacrylamide gel electrophoresis, and autoradiography. When intact cells were surface-labeled and incubated in the absence of insulin, the alpha and beta receptor subunits were clearly observed in the plasma membrane fraction and their quantities in the microsomal membrane fractions paralleled plasma membrane contamination. Following receptor internalization, however, both subunits were decreased in the plasma membrane fraction by 20-30% and concomitantly and stoichiometrically increased in the high and low density microsomal membrane fractions, without alterations in either their apparent molecular size or proportion. In contrast, when the isolated particulate membrane fractions were directly iodinated, both subunits were labeled in the plasma membrane fraction whereas only the beta subunit was prominently labeled in the two microsomal membrane fractions. Iodination of the subcellular fractions following their solubilization in Triton X-100 again clearly labeled both subunits in all three membrane fractions in identical proportions. These results suggest that 1) insulin receptor internalization comprises the translocation of both major receptor subunits from the plasma membrane into at least two different intracellular membrane compartments associated, respectively, with the endoplasmic reticulum and Golgi-enriched membrane fractions, 2) this translocation occurs without receptor loss or alterations in receptor subunit structure, and 3) the alpha receptor subunit is primarily, if not exclusively, exposed on the extracellular surface of the plasma membrane while the beta receptor subunit traverses the membrane, and this vectorial disposition is inverted during internalization.

Adipose Tissue↗
PubMed1984

Internalization of insulin and its receptor in the isolated rat adipose cell. Time-course and insulin concentration dependency.

The time-course and insulin concentration dependency of internalization of insulin and its receptor have been examined in isolated rat adipose cells at 37 degrees C. The internalization of insulin was assessed by examining the subcellular distribution of cell-associated [125I]insulin among plasma membrane, and high-density (endoplasmic reticulum-enriched) and low-density (Golgi-enriched) microsomal membrane fractions prepared by differential ultracentrifugation. The distribution of receptors was measured by the steady-state exchange binding of fresh [125I]insulin to these same membrane fractions. At 37 degrees C, insulin binding to intact cells is accompanied initially by the rapid appearance of intact insulin in the plasma membrane fraction, and subsequently, by its rapid appearance in both the high-density and low-density microsomal membrane fractions. An apparent steady-state distribution of insulin per mg of membrane protein among these subcellular fractions is achieved within 30 min in a ratio of 1:1.54:0.80, respectively. Concomitantly, insulin binding to intact cells is associated with the rapid disappearance of approx. 30% of the insulin receptors initially present in the plasma membrane fraction and appearance of 20-30% of those lost in the low-density microsomal membrane fraction. However, the number of receptors in the high-density microsomal membrane fraction does not change. This redistribution of receptors also appears to reach a steady-state within 30 min. Both processes are insulin concentration-dependent, correlating with receptor occupancy in the intact cell, and are partially inhibited at 16 degrees C. While the steady-state subcellular distributions of insulin and its receptor do not correlate with that of acid phosphatase, chloroquine markedly increases the levels of insulin associated with all three membrane fractions in apparent proportion to the distribution of this lysosomal marker enzyme activity, without more than marginally potentiating insulin's effects on the distribution of receptors. These results demonstrate that insulin, initially bound to the plasma membrane of the isolated rat adipose cell, is rapidly translocated by a receptor-mediated process into at least two intracellular compartments associated with the cell's high- and low-density microsomes. Furthermore, insulin simultaneously induces the translocation of its own receptor from the plasma membrane into the latter compartment. These translocations appear to represent the internalization and partial dissociation of the insulin-receptor complex through insulin-induced receptor cycling.

Adipose Tissue↗
PubMed1984

Counter-regulation of insulin-stimulated glucose transport by catecholamines in the isolated rat adipose cell.

The interaction between catecholamines and insulin in regulating glucose transport in isolated rat adipose cells has been evaluated. In the absence of insulin, 1 microM isoproterenol stimulates 3-O-methylglucose transport approximately 2-fold. However, isoproterenol in combination with adenosine deaminase inhibits glucose transport activity approximately 60%. N6-Phenylisopropyladenosine, a nonmetabolizable adenosine analogue, substantially reverses this inhibitory effect and actually stimulates glucose transport activity approximately 2-fold in the absence of isoproterenol. Dibutyryl cAMP inhibits glucose transport activity approximately 75% regardless of adenosine deaminase. While none of these agents significantly influences the basal concentration of plasma membrane glucose transporters, as assessed by specific D-glucose-inhibitable cytochalasin B binding, isoproterenol or dibutyryl cAMP in combination with adenosine deaminase reduces that in the low density microsomes 19 and 58%, respectively. In the presence of insulin, both isoproterenol and adenosine deaminase alone inhibit glucose transport activity approximately 25%. However, only the latter is accompanied by a corresponding decrease in the insulin-stimulated concentration of plasma membrane glucose transporters. Together, isoproterenol and adenosine deaminase inhibit insulin-stimulated glucose transport activity approximately 75%, even in the presence of 5 mM glucose to maintain cellular ATP levels. A similar inhibition is observed with dibutyryl cAMP. However, these agents decrease the insulin-stimulated concentration of plasma membrane glucose transporters only approximately 45%. Nevertheless, all of these inhibitory effects occur through decreases in the transport Vmax. In addition, N6-phenylisopropyladenosine partially reverses the inhibitory effects induced by the presence of adenosine deaminase. These results suggest that catecholamines counter-regulate basal and insulin-stimulated glucose transport in rat adipose cells through a cAMP-mediated mechanism, but only in part by modulating the translocation of glucose transporters.

3-O-Methylglucose↗
PubMed1984

Potential mechanism of the stimulatory action of insulin on insulin-like growth factor II binding to the isolated rat adipose cell. Apparent redistribution of receptors cycling between a large intracellular pool and the plasma membrane.

Previous studies have proposed that insulin increases the binding of insulin-like growth factor II (IGF-II) in isolated rat adipose cells at 24 degrees C by increasing receptor affinity (Ka). This study re-examines these observations under conditions in which receptor-ligand internalization is blocked by 1 mM KCN. In the absence of KCN, adipose cells bind 0.71 amol of IGF-II/cell with low apparent affinity (0.030 nM-1), of which greater than 75% is not accessible to trypsin. In contrast, in the presence of KCN, IGF-II binding is decreased by 95% and its apparent affinity increased to 0.21 nM-1. Moreover, greater than 60% of the bound IGF-II now is sensitive to trypsin. In either the absence or presence of KCN, approximately 20% of the cell's total IGF-II receptors are present in the plasma membranes and approximately 80% in the low density microsomes. Insulin induces a 5-fold increase in cell surface IGF-II receptors without a change in affinity when IGF-II binding is measured in the presence of KCN. Similarly, insulin increases IGF-II receptor concentration in the plasma membranes and concomitantly decreases that in the low density microsomes. Receptor affinity in these two subcellular membrane fractions is not affected by incubation of intact cells with either insulin or KCN and is similar to that observed in intact cells in the presence of KCN. Addition of KCN prior to insulin abolishes all of these effects of insulin. These data suggest that (a) the effects of KCN reflect a selective blockade of endocytosis; (b) in the absence of KCN, IGF-II binds to receptors of constant affinity that cycle between the plasma membrane and an intracellular pool resulting in an accumulation of intracellular IGF-II; (c) insulin induces an increase in IGF-II binding by causing a steady state redistribution of receptors from this intracellular pool to the plasma membrane; and (d) this redistribution in the intact cell can only be detected using Scatchard analysis when recycling of the receptors is prevented by KCN.

Adipose Tissue↗