The peripheral immune response in hyperglycemic stroke

OBJECTIVES

Hyperglycemia is common in acute ischemic stroke patients and is associated with poor clinical outcome. However, aggressive reduction of post-stroke hyperglycemia did not improve clinical outcome, suggesting that other mechanisms are playing a detrimental role in hyperglycemic stroke. We hypothesize that the acute post-stroke immune response is altered in the hyperglycemic state leading to higher mortality and morbidity. The objective of this study was to characterize temporal changes in circulating immune cells after stroke and their association with clinical outcomes in hyperglycemic compared to euglycemic patients.

PATIENTS AND METHODS

This retrospective study included 97 (58 % euglycemic, 42 % hyperglycemic) patients presenting within 12 h of symptom onset of stroke. Blood neutrophil, monocyte and lymphocyte concentrations were measured sequentially for 96 h post stroke. Primary clinical outcome was the difference in the NIH stroke scale at admission compared to discharge. Secondary outcome measures included discharge disposition and the modified Rankin Scale (mRS) at 90 days.

RESULTS

Circulating neutrophils were significantly higher in hyperglycemic than in euglycemic patients within the first 48 h post stroke, while lymphocyte counts trended to be lower. Hyperglycemic patients had higher mortality rates, less favorable discharge disposition and worse neurological function at 90 days. In both groups, the neutrophil to lymphocytes ratio ((NLR) remained strongly associated with neurological function at discharge within the first 24 h (p < 0.001), and remained significant in hyperglycemic patients up to 48 h (p < 0.001). Multivariate regression analysis showed no confounding by other factors and a significant correlation with differences in NIHSS score (CI; - 9.287 to -1.46, p = 0.0077**) and NLR (CL; 0.6058-6.901, p = 0.0203*) in hyperglycemic patients.

CONCLUSIONS

Our data suggests that circulating immune cells play an important role in mediating poor clinical outcome in hyperglycemic patients following stroke. The NLR is a strong predictor of neurological outcomes in hyperglycemic patients. Thus, the modulation of immune cells may be a viable therapeutic approach to improve outcomes for this high risk group.

Does the response to aspirin and clopidogrel vary over 6 months in patients with ischemic heart disease?

BACKGROUND

Dual-antiplatelet therapy (DAPT) with aspirin and a P2Y12 inhibitor, mostly clopidogrel, is the default therapy in both acute coronary syndrome (ACS) and after intracoronary stents. It is well established that responses to antiplatelet therapy (APT), particularly clopidogrel, are subject to considerable interindividual variability.

OBJECTIVES

We investigated whether responses to APT in individuals vary significantly over time.

METHODS

Simultaneous assay with VerifyNow(™) and short thrombelastography (s-TEG) was performed before and at four time points over 6 months after hospital discharge in 40 patients receiving DAPT. Serum thromboxane B2 levels were also measured.

RESULTS

While aspirin response units (ARU) by VerifyNow(™) and serum thromboxane B2 levels remained stable over time, arachidonic acid (AA)-mediated platelet aggregation with s-TEG (i.e. area under the curve at 15 min in AA channel, AUC15AA ) increased at 1 week compared with predischarge (P < 0.008). In addition, platelet reactivity units (PRU) by VerifyNow(™) (P = 0.046) and adenosine diphosphate (ADP)-mediated platelet aggregation with s-TEG (i.e. AUC15ADP ) also increased at 1 week compared with predischarge (P = 0.026). There were no significant changes in either platelet reactivity or rates of high on-treatment platelet reactivity while receiving clopidogrel beyond 1 week.

CONCLUSIONS

This study demonstrates important variability in responses to APT within individuals between predischarge and 1 week but not thereafter. The use of a single early (predischarge) platelet function assay as an indicator of future response may therefore be flawed. The design of future strategies to assess individual responses for tailored therapy needs to take this into account.

Takotsubo (apical ballooning) syndrome in the recovery period following dobutamine stress echocardiography: a first report

We report a case of Takotsubo syndrome occurring in the recovery phase after a dobutamine stress echocardiogram. Takotsubo syndrome is a widely acknowledged cause of reversible left ventricular systolic dysfunction. It has garnered much attention from the cardiological community since its presentation frequently mimics that of ST-segment elevation myocardial infarction. The exact aetiology remains incompletely defined, although stress is recognized frequently as a precipitating factor. In recent years it has emerged that stress testing, as part of a patient's investigative assessment, can also induce Takotsubo's syndrome. All prior reports of dobutamine-induced Takotsubo's syndrome have described apical ballooning at peak stress. We describe the case of an 85-year-old lady who developed apical ballooning in the recovery period after a dobutamine stress echocardiogram, despite having normal left ventricular wall motion at rest and at peak stress. We believe this to be the first such case reported in the literature. Dobutamine stress testing can precipitate Takotsubo's syndrome not just at peak stress but also during the recovery period. All those performing dobutamine stress tests should be aware of this rare but potentially important complication.

Improved membrane protein solubilization and clean-up for optimum two-dimensional electrophoresis utilizing GLUT-1 as a classic integral membrane protein

Two-dimensional (2-D) electrophoresis remains a primary resolving tool for proteomic analyses. The final number of proteins resolved by 2-D electrophoresis depends on their respective solubility, size, charge, and isoelectric point. While water-soluble cytosolic proteins have often been well represented in 2-D maps, the same is not true with membrane proteins. Highly hydrophobic in nature, membrane proteins are poorly resolved in 2-D gels due to problems associated primarily with sample preparation. This is of especial concern in neuroscience studies where many proteins of interest are membrane bound. In the current work, we present a substantially improved sample preparation protocol for membrane proteins utilizing the GLUT-1 glucose transporter from brain microvessels as an example of a typical membrane protein. GLUT-1 (SLC2A1; solute carrier family 2 (facilitated glucose transporter), member 1) is a 55kD glycoprotein that contains 12 membrane-spanning alpha helices that impart the protein its characteristic hydrophobicity. GLUT-1 based on its amino acid sequence has a theoretical isoelectric point (pI) of 8.94. Using a combination of the non-ionic detergents, n-dodecyl-beta-maltoside (DDM) and amido sulphobetaine-14 (ASB-14) for sample solubilization, and a modification of the Bio-Rad 2-D clean-up protocol involving trichloroacetic acid (TCA)/acetone, we obtained near complete solubilization of GLUT-1 and greater than 90% recovery of this membrane protein in 1-D and 2-D Western blots. The total number of proteins resolved also increased dramatically in Deep Purple total protein stains using our improved protocol.

An unusual atrial mass

Giant coronary artery aneurysm is a rare manifestation of coronary artery disease. This patient presented at echocardiography and was successfully managed by surgical resection.

Ferritin: a novel mechanism for delivery of iron to the brain and other organs

Traditionally, transferrin has been considered the primary mechanism for cellular iron delivery, despite suggestive evidence for additional iron delivery mechanisms. In this study we examined ferritin, considered an iron storage protein, as a possible delivery protein. Ferritin consists of H- and L-subunits, and we demonstrated iron uptake by ferritin into multiple organs and that the uptake of iron is greater when the iron is delivered via H-ferritin compared with L-ferritin. The delivery of iron via H-ferritin but not L-ferritin was significantly decreased in mice with compromised iron storage compared with control, indicating that a feedback mechanism exists for H-ferritin iron delivery. To further evaluate the mechanism of ferritin iron delivery into the brain, we used a cell culture model of the blood-brain barrier to demonstrate that ferritin is transported across endothelial cells. There are receptors that prefer H-ferritin on the endothelial cells in culture and on rat brain microvasculature. These studies identify H-ferritin as an iron transport protein and suggest the presence of an H-ferritin receptor for mediating iron delivery. The relative amount of iron that could be delivered via H-ferritin could make this protein a predominant player in cellular iron delivery.

Improving the positive predictive value of exercise testing in women

OBJECTIVE

To identify exercise test variables that can improve the positive predictive value of exercise testing in women.

DESIGN

Cohort study.

SETTING

Regional cardiothoracic centre.

SUBJECTS

1286 women and 1801 men referred by primary care physicians to a rapid access chest pain clinic, of whom 160 women and 406 men had ST depression of at least 1 mm during exercise testing. The results for 136 women and 124 men with positive exercise tests were analysed.

MAIN OUTCOME MEASURES

The proportion of women with a positive exercise test who could be identified as being at low risk for prognostic coronary heart disease and the resulting improvement in the positive predictive value.

RESULTS

Independently of age, an exercise time of more than six minutes, a maximum heart rate of more than 150 beats/min, and an ST recovery time of less than one minute were the variables that best identified women at low risk. One to three of these variables identified between 11.8% and 41.2% of women as being at low risk, with a risk for prognostic disease of between 0-11.5%. The positive predictive value for the remaining women was improved from 47.8% up to 61.5%, and the number of normal angiograms was potentially reducible by between 21.1-54.9%. By the same criteria, men had higher risks for prognostic disease.

CONCLUSIONS

A strategy of discriminating true from false positive exercise tests is worthwhile in women but less successful in men.

Distribution of divalent metal transporter 1 and metal transport protein 1 in the normal and Belgrade rat

Iron accumulation in the brain occurs in a number of neurodegenerative diseases. Two new iron transport proteins have been identified that may help elucidate the mechanism of abnormal iron accumulation. The Divalent Metal Transporter 1 (DMT1), is responsible for iron uptake from the gut and transport from endosomes. The Metal Transport Protein 1 (MTP1) promotes iron export. In this study we determined the cellular and regional expression of these two transporters in the brains of normal adult and Belgrade rats. Belgrade rats have a defect in DMT1 that is associated with lower levels of iron in the brain. In the normal rat, DMT1 expression is highest in neurons in the striatum, cerebellum, thalamus, ependymal cells lining the third ventricle, and vascular cells throughout the brain. The staining in the ependymal cells and endothelial cells suggests that DMT1 has an important role in iron transport into the brain. In Belgrade rats, there is generalized decrease in immunodetectable DMT1 compared to normal rats except in the ependymal cells. This decrease in immunoreactivity, however, was absent on immunoblots. The immunoblot analysis indicates that this protein did not upregulate to compensate for the chronic defect in iron transport. MTP1 staining is found in most brain regions. MTP1 expression in the brain is robust in pyramidal neurons of the cerebral cortex but is not detected in the vascular endothelial cells and ependymal cells. MTP1 staining in Belgrade rats was decreased compared to normal, but similar to DMT1 this decrease was not corroborated by immunoblotting. These results indicate that DMT1 and MTP1 are involved in brain iron transport and this involvement is regionally and cellularly specific.

Glucose transporter asymmetries in the bovine blood-brain barrier

The transport of glucose across the mammalian blood-brain barrier is mediated by the GLUT1 glucose transporter, which is concentrated in the endothelial cells of the cerebral microvessels. Several studies supported an asymmetric distribution of GLUT1 protein between the luminal and abluminal membranes (1:4) with a significant proportion of intracellular transporters. In this study we investigated the activity and concentration of GLUT1 in isolated luminal and abluminal membrane fractions of bovine brain endothelial cells. Glucose transport activity and glucose transporter concentration, as determined by cytochalasin B binding, were 2-fold greater in the luminal than in the abluminal membranes. In contrast, Western blot analysis using a rabbit polyclonal antibody raised against the C-terminal 20 amino acids of GLUT1 indicated a 1:5 luminal:abluminal distribution. Western blot analysis with antibodies raised against either the intracellular loop of GLUT1 or the purified erythrocyte protein exhibited luminal:abluminal ratios of 1:1. A similar ratio was observed when the luminal and abluminal fractions were exposed to the 2-N-4[(3)H](1-azi-2,2,2,-trifluoroethyl)benzoxyl-1,3-bis-(d-mannos-4-yloxyl)-2-propylamine ([(3)H]ATB-BMPA) photoaffinity label. These observations suggest that either an additional glucose transporter isoform is present in the luminal membrane of the bovine blood-brain barrier or the C-terminal epitope of GLUT1 is "masked" in the luminal membrane but not in the abluminal membranes.

Sex differences in investigation results and treatment in subjects referred for investigation of chest pain

OBJECTIVE

To evaluate differences in investigation results and treatment between men and women referred for diagnostic treadmill exercise testing and coronary arteriography.

DESIGN

Cohort study.

SETTING

Tertiary cardiology centre.

SUBJECTS

1522 subjects referred by primary care physicians to an open access chest pain clinic for initial investigation of chest pain, of whom 485 were subsequently referred for coronary arteriography; and a similar cohort of 107 subjects referred directly by secondary care physicians for diagnostic coronary arteriography.

MAIN OUTCOME MEASURES

Rates of positive exercise tests and rates for referral for arteriography and revascularisation according to sex.

RESULTS

Overall, women were less likely to be referred for arteriography and revascularisation than men. However, men were more likely to have positive exercise tests, and for various exercise test diagnostic end points men were also more likely to have significant coronary artery disease. After taking this into account, there was no sex difference in referral rates for arteriography or revascularisation.

CONCLUSIONS

There was no evidence of a sex bias resulting in inappropriate underinvestigation or undertreatment of women. However, the positive predictive value of treadmill exercise testing is low for women and further research is needed into how best to investigate women with chest pain.

Experimental stroke in the female diabetic, db/db, mouse

Diabetic hyperglycemia increases brain damage after cerebral ischemia in animals and humans, although the underlying mechanisms remain unclear. Gender-linked differences in ischemic tolerance have been described but have not been studied in the context of diabetes. In the current study, we used a model of unilateral common carotid artery ligation, combined with systemic hypoxia, to study the effects of diabetes and gender on hypoxic-ischemic (HI) brain damage in the genetic model of Type II diabetes, the db/db, mouse. Male and female, control and db/db, mice were subjected to right common carotid artery ligation followed by varying periods of hypoxia (8% oxygen/92% nitrogen) to assess mortality, infarct volume, and tissue damage by light microscopic techniques. End-ischemic regional cerebral blood flow (CBF) was determined using [14C] iodoantipyrine autoradiography. Glycolytic and high energy phosphate compounds were measured in blood and brain by enzymatic and fluorometric techniques. Gender and diabetes had significant effects on mortality from HI and extent of brain damage in the survivors. Female mice were more resistant than their male counterparts, such that the severity (mortality and infarction size) in the male diabetics > female diabetics - male controls > female controls. Endischemic CBF and depletion of cerebral high energy reserves were comparable among all groups. Surprisingly, female diabetic mice were more hyperglycemic and demonstrated a greater prolonged lactacidosis than the males; however, they were more resistant to damage. The results suggest a unique pathophysiology of hypoxia-ischemia in the female diabetic brain.

Prenatal expression of the GLUT4 glucose transporter in the mouse

The GLUT4 glucose transporter is primarily expressed in skeletal muscle, heart and adipose tissue, where its expression is postnatal, coincident with the acquisition of insulin-regulated glucose transport. In muscle, contraction also regulates GLUT4 activity in the postnatal animal. Here we demonstrate that GLUT4 is expressed in the developing mouse embryo with specific tissue and spatiotemporal patterns. From embryonic day 9 (E9; E1 = day of copulation plug) to postnatal day 70 (P70), mice were analyzed for GLUT4 mRNA and protein expression by in situ hybridization, immunohistochemistry and immunoblot. Specificity was confirmed with sense riboprobe hybridization and peptide competition, respectively. At E9, GLUT4 was detected in the cranial neural folds in the outer (mantle) layer of the neuroepithelium. At E10, expression was present throughout the developing heart and was prominent in the endocardial cushions through E12. At E10-12, GLUT4 was also prominent in craniofacial mesenchyme. GLUT4 expression in cartilage and bone was evident at E12 and was maintained throughout early postnatal life. GLUT4 was apparent throughout embryonic development in the ventricular epithelium, choroid plexus and in the developing cerebellum. At birth, cardiac expression was reduced and GLUT4 was most evident in cartilage, bone and specific brain regions. In the latter, GLUT4 expression was most evident in the cerebellum, specifically in the external granular layer through P7 and in the internal granular layer thereafter. Maximal GLUT4 protein levels in the cerebellum were measured between P14 and P21 and were reduced in the adult brain. These findings suggest that GLUT4-mediated glucose transport may play important roles during development of the brain and nonneuronal tissues in the mouse embryo.

Dehydroascorbic acid transport by GLUT4 in Xenopus oocytes and isolated rat adipocytes

Dehydroascorbic acid (DHA), the first stable oxidation product of vitamin C, was transported by GLUT1 and GLUT3 in Xenopus laevis oocytes with transport rates similar to that of 2-deoxyglucose (2-DG), but due to inherent difficulties with GLUT4 expression in oocytes it was uncertain whether GLUT4 transported DHA (Rumsey, S. C. , Kwon, O., Xu, G. W., Burant, C. F., Simpson, I., and Levine, M. (1997) J. Biol. Chem. 272, 18982-18989). We therefore studied DHA and 2-DG transport in rat adipocytes, which express GLUT4. Without insulin, rat adipocytes transported 2-DG 2-3-fold faster than DHA. Preincubation with insulin (0.67 micrometer) increased transport of each substrate similarly: 7-10-fold for 2-DG and 6-8-fold for DHA. Because intracellular reduction of DHA in adipocytes was complete before and after insulin stimulation, increased transport of DHA was not explained by increased internal reduction of DHA to ascorbate. To determine apparent transport kinetics of GLUT4 for DHA, GLUT4 expression in Xenopus oocytes was reexamined. Preincubation of oocytes for >4 h with insulin (1 micrometer) augmented GLUT4 transport of 2-DG and DHA by up to 5-fold. Transport of both substrates was inhibited by cytochalasin B and displayed saturable kinetics. GLUT4 had a higher apparent transport affinity (K(m) of 0.98 versus 5.2 mm) and lower maximal transport rate (V(max) of 66 versus 880 pmol/oocyte/10 min) for DHA compared with 2-DG. The lower transport rate for DHA could not be explained by binding differences at the outer membrane face, as shown by inhibition with ethylidene glucose, or by transporter trans-activation and therefore was probably due to substrate-specific differences in transporter/substrate translocation or release. These novel data indicate that the insulin-sensitive transporter GLUT4 transports DHA in both rat adipocytes and Xenopus oocytes. Alterations of this mechanism in diabetes could have clinical implications for ascorbate utilization.

Clopidogrel for prevention of major cardiac events after coronary stent implantation: 30-day and 6-month results in patients with smaller stents

OBJECTIVES

We developed this study to assess the procedural outcome, complications, and clinical follow-up in patients treated with different antiplatelet regimens after intracoronary stent implantation with small stents. Three hundred sixty-one consecutive patients, in whom at least one 3.0-mm intracoronary stent was implanted, were studied.

METHODS

The study was a prospective, observational registry of unselected consecutive patients treated in our institution. Patients who underwent stent implantation between December 1997 and July 1998 were treated with aspirin and ticlopidine; those who received stents between August 1998 and February 1999 were treated with aspirin and clopidogrel.

RESULTS

In the group treated with ticlopidine, there were 190 patients who had 253 lesions treated with 274 stents. Mean age was 59.1 years, 72% were male, 31% had unstable angina, 64% had 1 stent, 36% had >1 stent, and 23% had multivessel intervention. In the group treated with clopidogrel, there were 171 patients who had 226 lesions treated with 245 stents. Mean age was 60.4 years, 79% were male, 26% had unstable angina, 70% had 1 stent, 30% had >1 stent, and 26% had multivessel intervention. Complications at 30 days in the ticlopidine group were death in 1 (0.5%), stent occlusion in 3 (1. 6%; all reopened with repeat angioplasty), non-Q-wave myocardial infarction in 2 (1%), and urgent revascularization in 4 (2%). Complications at 30 days in the clopidogrel group were noncardiac death in 1 (1.2%), cardiac death in 1 (1.2%), stent occlusion in 0, non-Q-wave myocardial infarction in 3 (1.8%), and urgent revascularization in 0. Follow-up was available in 100% of patients in both groups (mean 253 +/- 75 days in the ticlopidine group, 198 +/- 53 days in the clopidogrel group). Complications at >30 days in the ticlopidine group were death in 1 and clinical restenosis in 11 (5.8%); 1 additional patient had an admission with unstable angina to the local hospital. Hence, recurrent angina as a consequence of target lesion restenosis occurred in 5.8%. Complications at >30 days in the clopidogrel group were death in 0 and clinical restenosis in 8 (4.7%); 2 additional patients were admitted with unstable angina to the local hospital, and 1 patient had a myocardial infarction 164 days after stent implantation. Hence, recurrent angina as a consequence of target lesion restenosis occurred in 4.7%. There were no significant differences in complications between the 2 groups.

CONCLUSIONS

Our observations suggest that clopidogrel can be used instead of ticlopidine in patients treated with stents with a diameter of </=3.0 mm, without any increase in major adverse cardiac events, both within the first 30 days and at medium-term follow-up. Clopidogrel has significant cost advantages over ticlopidine, and carries a superior side-effect profile. We suggest that, in combination with aspirin, clopidogrel should replace ticlopidine as standard antiplatelet therapy after intracoronary stent implantation.

Glucose transporter expression in brain: relationship to cerebral glucose utilization

Glucose is the principle energy source for mammalian brain. Delivery of glucose from the blood to the brain requires its transport across the endothelial cells of the blood-brain barrier and across the plasma membranes of neurons and glia, which is mediated by the facilitative glucose transporter proteins. The two primary glucose transporter isoforms which function in cerebral glucose metabolism are GLUT1 and GLUT3. GLUT1 is the primary transporter in the blood-brain barrier, choroid plexus, ependyma, and glia; GLUT3 is the neuronal glucose transporter. The levels of expression of both transporters are regulated in concert with metabolic demand and regional rates of cerebral glucose utilization. We present several experimental paradigms in which alterations in energetic demand and/or substrate supply affect glucose transporter expression. These include normal cerebral development in the rat, Alzheimer's disease, neuronal differentiation in vitro, and dehydration in the rat.

Cerebral glucose utilization and glucose transporter expression: response to water deprivation and restoration

The relationship between local rates of cerebral glucose utilization (ICMRglc) and glucose transporter expression was examined during physiologic activation of the hypothalamoneurohypophysial system. Three days of water deprivation, which is known to activate the hypothalamoneurohypophysial system, resulted in increased ICMRglc and increased concentrations of GLUT1 and GLUT3 in the neurohypophysis; mRNA levels of GLUT1 and GLUT3 were decreased and increased, respectively. Water deprivation also increased ICMRglc in the hypothalamic supraoptic and paraventricular nuclei; mRNA levels of GLUT1 and GLUT3 appeared to increase in these nuclei, but the changes did not achieve statistical significance. Restoration of water for 3 to 7 days reversed all observed changes in GLUT expression (protein and mRNA): restoration of water also reversed changes in ICMRglc in both the neurohypophysis and the hypothalamic nuclei. These results indicate that under conditions of neural activation and recovery, changes in ICMRglc and the levels of GLUT1 and GLUT3 are temporally correlated in the neurohypophysis and raise the possibility that GLUT1 and GLUT3 transporter expression may be regulated by chronic changes in functional activity. In addition, increases in the expression of GLUT5 mRNA in the neurohypophysis after dehydration provide evidence for involvement of microglial activation.

Alterations in blood-brain barrier glucose transport in SIV-infected macaques

The neurological manifestations of HIV infection may be in part due to alterations in the blood-brain barrier. These may be caused by structural changes in the barrier or may consist of subtle metabolic or biochemical disturbances in barrier function. In the CNS, the family of glucose transporter proteins plays a key role in controlling movement of glucose across cell membranes. The 55 kDa isoform of glucose transporter 1 (GLUT1) regulates import of glucose from blood to brain across the endothelial cells of the blood-brain barrier (BBB), whereas the 45 kDa form of GLUT1 predominantly regulates nonvascular glial glucose uptake. In this study, expression of 55 and 45 kDa forms of GLUT1 in different regions of the brain from 18 SIV-infected macaques was measured by quantitative immunoblot and then compared with the severity of SIV encephalitis to determine whether neurologic disease is related to altered glucose metabolism at the BBB and in brain parenchyma. An inverse relationship was found between severity of SIV encephalitis and expression of the endothelial 55 kDa isoform of GLUT1 at the BBB in cortical grey matter, caudate nucleus, and cerebellum. A similar relationship also was found for the glial 45 kDa GLUT1 isoform in cortical grey matter. In addition, a significant increase in 55 kDa GLUT1 expression was found in caudate nucleus during the early stages of infection. In the brains of macaques with moderate to severe encephalitis, 55 kDa GLUT1 expression had declined to pre-infection levels. These GLUT1 alterations at the BBB and in glial cells may reflect severe disturbances in the CNS microenvironment that contribute to CNS dysfunction.

Rest and exercise Doppler hemodynamics of the Medtronic Intact aortic bioprosthesis

BACKGROUND AND AIMS OF THE STUDY

Exercise treadmill testing was used to evaluate the functional rest and stress hemodynamic profile of the Medtronic Intact aortic bioprosthesis.

METHODS

A group of 93 patients (mean age at operation 72.9 years; range: 61-79 years) was studied. Mean time to follow up was 20.8 months. The preoperative diagnosis was aortic stenosis (AS; n = 66), aortic regurgitation (AR; n = 19) or AS/AR (n = 8). Left ventricular function was assessed as normal (n = 78), moderate (n = 14) or poor (n = 1). Patients received a range of valve sizes: 21 mm (n = 7); 23 mm (n = 41); 25 mm (n = 32); 27 mm (n = 7); and 29 mm (n = 6).

RESULTS

For all valve sizes, Doppler-derived hemodynamics at rest and peak exercise, respectively were: mean aortic valve gradient (AVG) 13.2 +/- 5.2 mmHg and 22.2 +/- 8.9 mmHg; peak aortic valve gradient (AVG) 24.3 +/- 9.6 mmHg and 39.1 +/- 13.5 mmHg; effective orifice area (EOA) 1.39 +/- 0.49 cm2 and 1.38 +/- 0.5 cm2; and effective orifice area index (EOAI) 0.76 +/- 0.26 cm2/m2 and 0.75 +/- 0.26 cm2/m2. Mean and peak AVG decreased as valve sizes increased, while both EOA and EOAI increased as valve sizes increased.

CONCLUSIONS

The Medtronic Intact aortic bioprosthesis provides good hemodynamics both at rest and exercise, across the range of implanted valve sizes.

Recurrent pericardial effusion: the value of polymerase chain reaction in the diagnosis of tuberculosis

A 23 year old army man presented with progressive dyspnoea and was found to have a massive pericardial effusion. Despite extensive investigations the cause remained elusive, until samples were sent for polymerase chain reaction (PCR). This case was unusual for several reasons and is a reminder of the atypical way in which tuberculosis infection can present and how a high index of suspicion should be maintained. It shows the importance of molecular biological advances in providing simple and rapid methods for arriving at the correct diagnosis, by way of nucleic acid probes and polymerase chain reaction.

Interpreting early land management through compound specific stable isotope analyses of archaeological soils

Compound specific stable isotope analyses of managed soils using isotope ratio mass spectrometry have been undertaken as a means of determining early land use practices. delta (15)N amino acid signals demonstrate differences between manured grassland, unmanured grassland and continuous cereal cultivation under long-term experimental land use control conditions, with delta (15)N in hydrophobic amino acids providing the most distinctive signals. Analysis of early modern/medieval and of Bronze age anthropogenic soils from Orkney demonstrates that such signals are retained in archaeological contexts. delta (13)C analyses of n- alkanoic acid components of the fossil, Bronze Age, anthropogenic soils suggest a major terrestrial input to these soils, with uniform composition of formation materials. Surficial soils demonstrate the assimilation of isotopically lighter carbon, providing a means of assessing the mobility of the n- alkanoic acids within soils and sediments. Copyright 1999 John Wiley & Sons, Ltd.

Astrocytic demise precedes delayed neuronal death in focal ischemic rat brain

Active neuronal-glial interaction is important in the maintenance of brain homeostasis and is vital for neuronal survival following brain injury. The time course of post-ischemic astroglial dysfunction and neuronal death was studied in the spontaneously hypertensive rat (SHR) brain following permanent middle cerebral artery occlusion (MCAO). In situ hybridization with 35S-labeled riboprobes for GFAP and GLUT3 was used to monitor mRNA expression in glia and neurons. Astrocytic proteins GFAP, vimentin, S100, Glutathione-S-Transferase Yb (GST Yb) and neuronal protein TG2 were detected by immunofluorescence. Cells were co-stained with in situ end labeling (ISEL) to detect DNA fragmentation, a hallmark of cell death. GFAP mRNA expression declined rapidly in the ischemic region of the cortex and was almost absent by 12 h. Immunohistochemical studies revealed a parallel decline in the corresponding protein: a reduction in GFAP staining was apparent in the infarct after 3 h and by 24 h, there was essentially no remaining GFAP. Three other glial proteins (vimentin, S100 and GST Yb) disappeared from infarct over a similar time course. A few ISEL positive cells were observed in the infarct at 6 h, but maximal detection was not seen until 24-48 h. Most of the ISEL-positive cells were neurons, identified by co-staining with the neuronal marker TG2. Few cells expressing GFAP or other glial markers were positive at any time point. Neuronal GLUT3 mRNA declined more slowly than GFAP mRNA in the ischemic core and disappeared during the period of neuronal death. Concurrent with the loss of GFAP mRNA and protein expression in the infarct, there was a rapid rise in GFAP mRNA in the peri-infarct region of ipsilateral hemisphere and proximal region of the contralateral hemisphere. This was followed by the enhanced GFAP protein expression characteristic of reactive astrocytes, but over a significantly slower time course. These studies show that MCAO leads to a rapid decline of GFAP mRNA and glial proteins, which appears to precede the decline in neuronal mRNA and neuronal death within the infarct. Early astroglial dysfunction may play a critical role in determining the outcome of acute hypoxic-ischemic injury by compromising neuronal-glial interactions.

Effects of barbiturates on facilitative glucose transporters are pharmacologically specific and isoform selective

Barbiturates inhibit GLUT-1-mediated glucose transport across the blood-brain barrier, in cultured mammalian cells, and in human erythrocytes. Barbiturates also interact directly with GLUT-1. The hypotheses that this inhibition of glucose transport is (i) selective, preferring barbiturates over halogenated hydrocarbon inhalation anesthetics, and (ii) specific, favoring some GLUT-# isoforms over others were tested. Several oxy- and thio-barbiturates inhibited [3H]-2-deoxyglucose uptake by GLUT-1 expressing murine fibroblasts with IC50s of 0.2-2.9 mm. Inhibition of GLUT-1 by barbiturates correlates with their overall lipid solubility and pharmacology, and requires hydrophobic side chains on the core barbiturate structure. In contrast, several halogenated hydrocarbons and ethanol (all </=10 mm) do not significantly inhibit glucose transport. The interaction of these three classes of anesthetics with purified GLUT-1 was evaluated by quenching of intrinsic protein fluorescence and displayed similar specificities and characteristics. The ability of barbiturates to inhibit other facilitative glucose transporters was determined in cell types expressing predominantly one isoform. Pentobarbital inhibits [3H]-2-deoxyglucose and [14C]-3-O-methyl-glucose uptake in cells expressing GLUT-1, GLUT-2, and GLUT-3 with IC50s of approximately 1 mm. In contrast, GLUT-4 expressed in insulin-stimulated rat adipocytes was much less sensitive than the other isoforms to inhibition by pentobarbital (IC50 of >10 mm). Thus, barbiturates selectively inhibit glucose transport by some, but not all, facilitative glucose transporter isoforms.

Blood-brain barrier glucose transporter: effects of hypo- and hyperglycemia revisited

The transport of glucose across the blood-brain barrier (BBB) is mediated by the high molecular mass (55-kDa) isoform of the GLUT1 glucose transporter protein. In this study we have utilized the tritiated, impermeant photolabel 2-N-[4-(1 -azi-2,2,2-trifluoroethyl)[2-3H]propyl]-1,3-bis(D-mannose-4-ylo xy)-2-propylamine to develop a technique to specifically measure the concentration of GLUT1 glucose transporters on the luminal surface of the endothelial cells of the BBB. We have combined this methodology with measurements of BBB glucose transport and immunoblot analysis of isolated brain microvessels for labeled luminal GLUT1 and total GLUT1 to reevaluate the effects of chronic hypoglycemia and diabetic hyperglycemia on transendothelial glucose transport in the rat. Hypoglycemia was induced with continuous-release insulin pellets (6 U/day) for a 12- to 14-day duration; diabetes was induced by streptozotocin (65 mg/kg i.p.) for a 14- to 21-day duration. Hypoglycemia resulted in 25-45% increases in regional BBB permeability-surface area (PA) values for D-[14C]glucose uptake, when measured at identical glucose concentration using the in situ brain perfusion technique. Similarly, there was a 23+/-4% increase in total GLUT1/mg of microvessel protein and a 52+/-13% increase in luminal GLUT1 in hypoglycemic animals, suggesting that both increased GLUT1 synthesis and a redistribution to favor luminal transporters account for the enhanced uptake. A corresponding (twofold) increase in cortical GLUT1 mRNA was observed by in situ hybridization. In contrast, no significant changes were observed in regional brain glucose uptake PA, total microvessel 55-kDa GLUT1, or luminal GLUT1 concentrations in hyperglycemic rats. There was, however, a 30-40% increase in total cortical GLUT1 mRNA expression, with a 96% increase in the microvessels. Neither condition altered the levels of GLUT3 mRNA or protein expression. These results show that hypoglycemia, but not hyperglycemia, alters glucose transport activity at the BBB and that these changes in transport activity result from both an overall increase in total BBB GLUT1 and an increased transporter concentration at the luminal surface.

Intracoronary Multi-link stents: experience in 218 patients using aspirin alone

OBJECTIVES

To assess procedural outcome, complications, and clinical follow up in 218 patients who underwent treatment with 297 Multi-link (Guidant) stents implanted without the use of intravascular ultrasound (IVUS) or quantitative coronary angiography (QCA), and using aspirin alone as antiplatelet therapy.

METHODS

The case records and angiograms were reviewed and the patients were contacted by telephone to determine their symptoms and any adverse events at follow up. Data were analysed using Fisher's exact test.

RESULTS

Of the 218 patients included in the study, 45 had multivessel intracoronary intervention, and 55 had unstable angina. The mean (SD) length of hospital stay following the procedure was 2.0 (2.1) days. There were two early deaths at less than 30 days, and two deaths during follow up at more than 100 days. Ten patients suffered complications during the first 30 days: four had subacute stent thrombosis, of whom two died and two were treated successfully with coronary artery bypass grafting; five had a non-Q wave myocardial infarction; and one had a femoral false aneurysm. Patient outcome was analysed according to stent diameter (3.0 mm or less, or 3.5 mm or more) and by angina status (stable or unstable). In patients in whom at least one stent was 3.0 mm diameter, four of 86 patients suffered acute stent occlusion, whereas in the 132 patients in whom all stents were at least 3.5 mm diameter there were no cases of stent occlusion (p = 0.02). In the unstable angina group two of 55 patients suffered acute stent occlusion compared to two of 163 patients in the stable angina group (NS). In patients with unstable angina and at least one stent of 3.0 mm diameter, the acute occlusion rate was 7.1% (two of 28 patients). Three of the four patients with stent occlusion had undergone complex procedures. Twenty eight patients were restudied for recurrent symptoms during the follow up period. Of these, eight patients had restenosis within their stent. In seven of these patients the stent size was 3.0 mm diameter, and in the remaining patient the stent size was 4.0 mm diameter. Three of the 28 patients restudied had developed new disease remote from the stented site, and 17 had patent stents and no significant other coronary lesion.

CONCLUSIONS

This study suggests that coronary intervention using the Multi-link stent is safe and effective using aspirin alone, without IVUS or QCA, when stent diameter is greater than 3.0 mm. All cases of stent occlusion in this series occurred in patients in whom at least one stent was 3.0 mm diameter, with stent occlusion being higher in patients with unstable angina compared to those with stable angina. Additional antiplatelet therapy may be beneficial in those patients in whom Multi-link stent diameter is less than 3.5 mm, particularly in those with unstable angina, but is not necessary for patients receiving Multi-link stents of 3.5 mm diameter or greater.

Monocarboxylate transporter expression in mouse brain

Although glucose is the major metabolic fuel needed for normal brain function, monocarboxylic acids, i.e., lactate, pyruvate, and ketone bodies, can also be utilized by the brain as alternative energy substrates. In most mammalian cells, these substrates are transported either into or out of the cell by a family of monocarboxylate transporters (MCTs), first cloned and sequenced in the hamster. We have recently cloned two MCT isoforms (MCT1 and MCT2) from a mouse kidney cDNA library. Northern blot analysis revealed that MCT1 mRNA is ubiquitous and can be detected in most tissues at a relatively constant level. MCT2 expression is more limited, with high levels of expression confined to testes, kidney, stomach, and liver and lower levels in lung, brain, and epididymal fat. Both MCT1 mRNA and MCT2 mRNA are detected in mouse brain using antisense riboprobes and in situ hybridization. MCT1 mRNA is found throughout the cortex, with higher levels of hybridization in hippocampus and cerebellum. MCT2 mRNA was detected in the same areas, but the pattern of expression was more specific. In addition, MCT1 mRNA, but not MCT2, is localized to the choroid plexus, ependyma, microvessels, and white matter structures such as the corpus callosum. These results suggest a differential expression of the two MCTs at the cellular level.

GLUT4 glucose transporter expression in rodent brain: effect of diabetes

This study describes the regional and cellular expression of the insulin-sensitive glucose transporter, GLUT4, in rodent brain. A combination of in situ hybridization, immunohistochemistry and immunoblot techniques was employed to localize GLUT4 mRNA and protein to the granule cells of the olfactory bulb, dentate gyrus of the hippocampus and the cerebellum, with the greatest level of expression being in the cerebellum. Estimates of the concentration of GLUT4 in cerebellar membranes indicate that this transporter isoform is present in significant amounts, relative to the other isoforms, GLUT1 and GLUT3. Cerebellar GLUT4 expression was increased in the genetically diabetic, hyperinsulinemic, db/db mouse relative to the non-diabetic control, and even higher levels were observed in db/db female than db/db male mice. Levels of expression of GLUT4 protein in cerebellum appear to respond to the level of circulating insulin, and are reduced in the hypoinsulinemic streptozotocin-diabetic rat. Exercise training also results in reduced insulin levels and comparably reduced levels of GLUT4 in the cerebellum. These studies demonstrate a chronic insulin-sensitive regulation of GLUT4 in rodent brain and raise the possibility of acute modulations of glucose uptake in these GLUT4 expressing cells.

Alterations in GLUT1 and GLUT3 glucose transporter gene expression following unilateral hypoxia-ischemia in the immature rat brain

The brain damage produced by unilateral cerebral hypoxia-ischemia in the immature rat results from major alterations in cerebral energy metabolism and glucose utilization which begin during the course of the insult and proceed into the recovery period. Consistent with a lack of pathology, the alterations in the hemisphere contralateral to the carotid artery ligation are transient and return to normal within 24 h of recovery, whereas the hemisphere ipsilateral to the ligation exhibits both early and late responses, and infarction. The facilitative glucose transporter proteins mediate glucose transport across the blood-brain barrier (55 kDa GLUT1), and into neurons and glia (GLUT3 and 45 kDa GLUT1), and demonstrate both early and late responses to perinatal hypoxia-ischemia. This study employed in situ hybridization histochemistry to investigate the temporal and regional patterns of GLUT1 and GLUT3 gene expression following a severe (2.5 h) hypoxic-ischemic insult in the 7-day old rat brain. Enhanced GLUT1 mRNA expression was apparent in cerebral microvessels of both hemispheres and remained elevated in the ipsilateral hemisphere through 24 h of recovery, consistent with our previous observation of increased microvascular 55 kDa GLUT1 protein. The expression of the neuronal isoform, GLUT3, was enhanced in penumbral regions, such as piriform cortex and amygdala, but was rapidly reduced in the affected areas of cortex, hippocampus and thalamus, reflecting necrosis. The late response, observed at 72 h of recovery, was characterized by extensive necrosis in the ipsilateral hemisphere, loss of GLUT3 expression, and a gliotic reaction including increased GLUT1 in GFAP-positive astrocytes. This study demonstrates that cerebral hypoxia-ischemia in the immature rat produces both immediate-early and long-term effects on the glucose transporter proteins at the level of gene expression.

Functional hemodynamic assessment of the 21-mm and 23-mm CarboMedics Top Hat aortic prosthetic valve

Between 1993 and 1996 the CarboMedics Top Hat supraannular aortic valve was implanted in 41 patients at the Wessex Cardiothoracic Centre (age, 39 to 74 years; mean, 61.3+/-8.9 years). Comparisons of annular dimensions made at surgery indicate that conventional annular valve replacement would have required at least a size smaller valve. This was particularly marked when a prosthetic mitral valve was in place. Operative mortality was 2.4%. There were also three late deaths. Echocardiography before and after symptom-limited treadmill testing has been performed in 21 patients. The mean time to follow-up was 16.1 months. The Doppler-derived indices of forward flow pre- and postexercise were expressed as mean+/-standard deviation. For 23-mm valves the values were: peak valve gradient 21.43+/-7.46 mm Hg and 35.86+/-14.4 mm Hg, aortic valve area 1.13+/-0.39 cm2 and 1.24+/-0.54 cm2. For 21-mm valves the values were: peak valve gradient 24.84+/-8.2 mm Hg and 31.29+/-5.84 mm Hg, aortic valve area 1.08+/-0.44 cm2 and 0.95 +/-0.2 cm2. The Top Hat valve has a good hemodynamic profile at rest and during exercise. Surgical considerations make it particularly useful in patients with a small aortic annulus and in patients undergoing combined aortic and mitral valve replacement.

Distinct localization of GLUT-1, -3, and -5 in human monocyte-derived macrophages: effects of cell activation

We determined subcellular localization of GLUT-1, GLUT-3, and GLUT-5 as human monocytes differentiate into macrophages in culture, and effects of the activating agents N-formyl-methionyl-leucyl-phenylalanine (fMLP) and phorbol myristate acetate (PMA). Western blot analysis demonstrated progressively increased GLUT-1, rapidly decreased GLUT-3, and a delayed increase of GLUT-5 expression during differentiation. Confocal microscopy revealed that each isoform displayed a unique subcellular distribution and cell-activation response. GLUT-1 was localized primarily to the cell surface but was also detected in the perinuclear region in a pattern characteristic of recycling endosomes. GLUT-3 exhibited predominantly a distinct vesicle-like staining but was present only in monocytes. GLUT-5 was found primarily at the cell surface but was detectable intracellularly. Activation with fMLP induced similar GLUT-1 and GLUT-5 redistributions from intracellular compartments toward the cell surface. PMA elicited a similar translocation of GLUT-1, but GLUT-5 was redistributed from the plasma membrane to a distinct intracellular compartment that appeared connected to the cell surface. These results suggest specific subcellular targeting of each transporter isoform and differential regulation of their trafficking pathways in cultured macrophages.

Thrombin-induced translocation of GLUT3 glucose transporters in human platelets

Platelets derive most of their energy from anaerobic glycolysis; during activation this requirement rises approx. 3-fold. To accommodate the high glucose flux, platelets express extremely high concentrations (155+/-18 pmol/mg of membrane protein) of the most active glucose transporter isoform, GLUT3. Thrombin, a potent platelet activator, was found to stimulate 2-deoxyglucose transport activity 3-5-fold within 10 min at 25 degrees C, with a half-time of 1-2 min. To determine the mechanism underlying the increase in glucose transport activity, an impermeant photolabel, [2-3H]2N-4-(1-azi-2,2,2-trifluoethyl)benzoyl-1,3, -bis-(d-mannose-4-ylozy)-2-propylamine, was used to covalently bind glucose transporters accessible to the extracellular milieu. In response to thrombin, the level of transporter labelling increased 2.7-fold with a half-time of 1-2 min. This suggests a translocation of GLUT3 transporters from an intracellular site to the plasma membrane in a manner analogous to that seen for the translocation of GLUT4 in insulin-stimulated rat adipose cells. To investigate whether a similar signalling pathway was involved in both systems, platelets and adipose cells were exposed to staurosporin and wortmannin, two inhibitors of GLUT4 translocation in adipose cells. Thrombin stimulation of glucose transport activity in platelets was more sensitive to staurosporin inhibition than was insulin-stimulated transport activity in adipose cells, but it was totally insensitive to wortmannin. This indicates that the GLUT3 translocation in platelets is mediated by a protein kinase C not by a phosphatidylinositol 3-kinase mechanism. In support of this contention, the phorbol ester PMA, which specifically activates protein kinase C, fully stimulated glucose transport activity in platelets and was equally sensitive to inhibition by staurosporin. This study provides a cellular mechanism by which platelets enhance their capacity to import glucose to fulfil the increased energy demands associated with activation.

Echocardiographic assessment of long axis function: a simple solution to a complex problem?

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Glucose transporter proteins in brain: delivery of glucose to neurons and glia

Glucose is the principle energy source for the mammalian brain. Delivery of glucose from the blood to the brain requires transport across the endothelial cells of the blood-brain barrier and into the neurons and glia. The facilitative glucose transporter proteins mediate these processes. The primary isoforms in brain are GLUT1, detected at high concentrations as a highly glycosylated form, (55 kDa) in blood-brain barrier, and also as a less glycosylated, 45 kDa form, present in parenchyma, predominantly glia; GLUT3 in neurons; and GLUT5 in microglia. The rest of the transporter family, GLUTs 2, 4, and 7, have also been detected in brain but at lower levels of expression and confined to more discrete regions. All of the transporters probably contribute to cerebral glucose utilization, as part of overall metabolism and metabolic interactions among cells. We discuss the properties, regulation, cell-specific location, and kinetic characteristics of the isoforms, their potential contributions to cerebral metabolism, and several experimental paradigms in which alterations in energetic demand and/or substrate supply affect glucose transporter expression.

The midcycle increase in ovarian glucose uptake is associated with enhanced expression of glucose transporter 3. Possible role for interleukin-1, a putative intermediary in the ovulatory process

This study characterizes the rat ovary as a site of hormonally dependent glucose transporter (Glut) expression, and explores the potential role of interleukin (IL)-1, a putative intermediary in the ovulatory process, in this regard. Molecular probing throughout a simulated estrous cycle revealed a significant surge in ovarian Glut3 (but not Glut1) expression at the time of ovulation. Treatment of cultured whole ovarian dispersates from immature rats with IL-1beta resulted in upregulation of the relative abundance of the Glut1 (4.5-fold) and Glut3 (3.5-fold) proteins as determined by Western blot analysis. Other members of the Glut family (i.e., Gluts 2, 4, and 5) remained undetectable. The ability of IL-1 to upregulate Glut1 and Glut3 transcripts proved time-, dose-, nitric oxide-, and protein biosynthesis-dependent but glucose independent. Other ovarian agonists (i.e., TNF alpha, IGF-I, interferon-gamma, and insulin) were without effect. Taken together, our findings establish the mammalian ovary as a site of cyclically determined Glut1 and Glut3 expression, and disclose the ability of IL-1 to induce the ovarian expression as well as translation of Glut1 and Glut3 (but not of Gluts 2, 4, or 5). Our observations also establish IL-1 as the first known regulator of Glut3, the most efficient Glut known to date. In so doing, IL-1, a putative component of the ovulatory process, may be acting to meet the increased metabolic demands imposed on the growing follicle and the ovulated cumulus-enclosed oocyte.

Glucose utilization and glucose transporter proteins GLUT-1 and GLUT-3 in brains of diabetic (db/db) mice

This study describes the effects of diabetes on brain growth, cerebral glucose utilization (CGU), and the glucose transporter proteins GLUT-1 and GLUT-3 in the genetically diabetic db/db mouse. Mice were studied at 5 and 10 wk of age and compared with age-matched nondiabetic littermates. At 5 wk, db/db mice were not yet hyperglycemic, but their body weights were 27.5% greater than those of their nondiabetic littermates. By 10 wk, db/db mice were both hyperglycemic (blood glucose values of 39.3 +/- 4.3 vs. 12.1 +/- 2.1 mmol/l for db/db and control, respectively) and obese, with a twofold increase in body weight. Significant reductions in brain weight were observed at 5 wk (15% decrease in brain wet wt), and no further brain growth was observed, such that by 10 wk, brains of db/db mice were 25% smaller than those of control mice; brain wet weight-to-dry weight ratios were slightly reduced. Global rates of CGU, as determined with 2-[14C]deoxyglucose, were significantly reduced in the 10-wk diabetic mice. Levels of brain glucose and brain-to-blood glucose ratios were increased in 5- and 10-wk db/db mice, reflecting adequate glucose delivery to the brain. Blood-brain barrier GLUT-1 levels were unchanged, and mRNA levels were regionally increased. The expression of the neuronal glucose transporter GLUT-3 was not reduced to a significant extent in brains of db/db mice. The results of this study indicate that the db/db mouse has markedly decelerated brain growth accompanied by global reductions in glucose metabolism that are not due to reductions in glucose transport capacity.

Human immunodeficiency virus type 1 infection of H9 cells induces increased glucose transporter expression

A clone obtained from a differential display screen for cellular genes with altered expression during human immunodeficiency virus (HIV) infection matched the sequence for the human GLUT3 facilitative glucose transporter, a high-velocity-high-affinity facilitative transporter commonly expressed in neurons of the central nervous system. Northern (RNA) analysis showed that GLUT3 expression increased during infection. Flow cytometry showed that GLUT3 protein expression increased specifically in the HIV-infected cells; this increase correlated with increased 2-deoxyglucose transport in the HIV-infected culture. HIV infection therefore leads to increased expression of a glucose transporter normally expressed at high levels in other cell types and a corresponding increase in glucose transport activity. If HIV infection places increased metabolic demands on the host cell, changes in the expression of a cellular gene that plays an important role in cellular metabolism might provide a more favorable environment for viral replication.

Substrate specificity and kinetic parameters of GLUT3 in rat cerebellar granule neurons

This study examines the apparent affinity, catalytic-centre activity ("turnover number') and stereospecificity of the neuronal glucose transporter GLUT3 in primary cultured cerebellar granule neurons. Using a novel variation of the 3-O-[14C]methylglucose transport assay, by measuring zero-trans kinetics at 25 degrees C, GLUT3 was determined to be a high-apparent-affinity, high-activity, glucose transporter with a K(m) of 2.87 +/- 0.23 mM (mean +/- S.E.M.) for 3-O-methylglucose, a Vmax of 18.7 +/- 0.48 nmol/min per 10(6) cells, and cells, and a corresponding catalytic-centre activity of 853 s-1. Transport of 3-O-methylglucose was competed by glucose, mannose, 2-deoxyglucose and galactose, but not by fructose. This methodology is compared with the more common 2-[3H]deoxyglucose methodology and the [U-14C]-glucose transport method. The high affinity and transport activity of the neuronal glucose transporter GLUT3 appears to be an appropriate adaptation to meet the demands of neuronal metabolism at prevailing interstitial brain glucose concentrations (1-2 mM).

Current status of flow convergence for clinical applications: is it a leaning tower of "PISA"?

Spatial appreciation of flow velocities using Doppler color flow mapping has led to quantitative evaluation of the zone of flow convergence proximal to a regurgitant orifice. Based on the theory of conservation of mass, geometric analysis, assuming a series of hemispheric shells of increasing velocity as flow converges on the orifice--the so-called proximal isovelocity surface area (PISA) effect--has yielded methods promising noninvasive measurement of regurgitant flow rate. When combined with conventional Doppler ultrasound to measure orifice velocity, regurgitant orifice area, the major predictor of regurgitation severity, can also be estimated. The high temporal resolution of color M-mode can be used to evaluate dynamic changes in orifice area, as seen in many pathologic conditions, which enhances our appreciation of the pathophysiology of regurgitation. The PISA methodology is potentially applicable to any restrictive orifice and has gained some credibility in the quantitative evaluation of other valve pathology, particularly mitral and tricuspid regurgitation, and in congenital heart disease. Although the current limitations of PISA estimates of regurgitation have tempered its introduction as a valuable clinical tool, considerable efforts in in vitro and clinical research have improved our understanding of the problems and limitations of the PISA methodology and provided a firm platform for continuing research into the accurate quantitative assessment of valve regurgitation and the expanding clinical role of quantitative Doppler color flow mapping.

Biological valves beyond fifteen years: the Wessex experience

Between 1975 and 1979, 443 biological valves (298 Carpentier-Edwards, 134 homograft, and 11 Hancock valves) were implanted in 415 patients (age, 16 to 77 years; mean, 59 years) with an operative mortality of 2.9%. Total follow-up was 4,248 patient-years. Overall event-free survival was 60% +/- 1.5% (standard deviation) at 10 years and 29% +/- 1.4% at 15 years. Ten-year and 15-year event-free survival were 72% +/- 3.4% and 41% +/- 3.3% for aortic homografts, 62% +/- 3% and 33% +/- 2.8% for isolated aortic xenografts, and 43% +/- 3.5% and 14% +/- 3.0% for isolated mitral xenografts. Freedom from structural valve degeneration was 87% +/- 1.3% and 63% +/- 2.5% for all patients at 10 and 15 years, respectively, 86% +/- 2.7% and 58% +/- 4.1% for aortic homografts, 93% +/- 1.8% and 76% +/- 5.1% for aortic xenografts, and 75% +/- 4.0% and 47% +/- 7.4% for mitral xenografts. Of the 110 remaining patients, echocardiography was performed in 61 patients (23 aortic xenograft, 24 aortic homograft, 9 mitral xenograft, and 5 tricuspid xenograft) between 14 and 17 years after implantation. An early diastolic murmur was heard in 57% of all aortic valve replacements (AVRs) 62.5% of homograft AVRs, and 52% of xenograft AVRs. Echocardiographically, aortic regurgitation was detected in 79%, 83%, and 74% of all AVRs, homografts, and xenografts, respectively. Aortic stenosis was present clinically in 11% of all AVRs, 4% of homograft AVRs, and 17% of xenograft AVRs.(ABSTRACT TRUNCATED AT 250 WORDS)

How to quantitate valve regurgitation by echo Doppler techniques. British Society of Echocardiography

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