A US perspective on closing the carbon cycle to defossilize difficult-to-electrify segments of our economy

Electrification to reduce or eliminate greenhouse gas emissions is essential to mitigate climate change. However, a substantial portion of our manufacturing and transportation infrastructure will be difficult to electrify and/or will continue to use carbon as a key component, including areas in aviation, heavy-duty and marine transportation, and the chemical industry. In this Roadmap, we explore how multidisciplinary approaches will enable us to close the carbon cycle and create a circular economy by defossilizing these difficult-to-electrify areas and those that will continue to need carbon. We discuss two approaches for this: developing carbon alternatives and improving our ability to reuse carbon, enabled by separations. Furthermore, we posit that co-design and use-driven fundamental science are essential to reach aggressive greenhouse gas reduction targets.

Electron transport through supercrystals of atomically precise gold nanoclusters: a thermal bi-stability effect

Nanoparticles (NPs) may behave like atoms or molecules in the self-assembly into artificial solids with stimuli-responsive properties. However, the functionality engineering of nanoparticle-assembled solids is still far behind the aesthetic approaches for molecules, with a major problem arising from the lack of atomic-precision in the NPs, which leads to incoherence in superlattices. Here we exploit coherent superlattices (or supercrystals) that are assembled from atomically precise Au103S2(SR)41 NPs (core dia. = 1.6 nm, SR = thiolate) for controlling the charge transport properties with atomic-level structural insights. The resolved interparticle ligand packing in Au103S2(SR)41-assembled solids reveals the mechanism behind the thermally-induced sharp transition in charge transport through the macroscopic crystal. Specifically, the response to temperature induces the conformational change to the R groups of surface ligands, as revealed by variable temperature X-ray crystallography with atomic resolution. Overall, this approach leads to an atomic-level correlation between the interparticle structure and a bi-stability functionality of self-assembled supercrystals, and the strategy may enable control over such materials with other novel functionalities.

Room-temperature wavelike exciton transport in a van der Waals superatomic semiconductor

The transport of energy and information in semiconductors is limited by scattering between electronic carriers and lattice phonons, resulting in diffusive and lossy transport that curtails all semiconductor technologies. Using Re6Se8Cl2, a van der Waals (vdW) superatomic semiconductor, we demonstrate the formation of acoustic exciton-polarons, an electronic quasiparticle shielded from phonon scattering. We directly imaged polaron transport in Re6Se8Cl2 at room temperature, revealing quasi-ballistic, wavelike propagation sustained for a nanosecond and several micrometers. Shielded polaron transport leads to electronic energy propagation lengths orders of magnitude greater than in other vdW semiconductors, exceeding even silicon over a nanosecond. We propose that, counterintuitively, quasi-flat electronic bands and strong exciton-acoustic phonon coupling are together responsible for the transport properties of Re6Se8Cl2, establishing a path to ballistic room-temperature semiconductors.

Roll-To-Roll Friendly Solution-Processing of Ultrathin, Sintered CdTe Nanocrystal Photovoltaics

Roll-to-roll (R2R) device fabrication using solution-processed materials is a cheap and versatile approach that has attracted widespread interest over the past 2 decades. Here, we systematically introduce and investigate R2R-friendly modifications in the fabrication of ultrathin, sintered CdTe nanocrystal (NC) solar cells. These include (1) scalable deposition techniques such as spray-coating and doctor-blading, (2) a bath-free, controllable sintering of CdTe NCs by quantitative addition of a sintering agent, and (3) radiative heating with an infrared lamp. The impact of each modification on the CdTe nanostructure and solar cell performance was first independently studied and compared to the standard, non-R2R-friendly procedure involving spin-coating the NCs, soaking in a CdCl₂ bath, and annealing on a hot plate. The R2R-friendly techniques were then combined into a single, integrated process, yielding devices that reach 10.4% power conversion efficiency with a V_oc, J_sc, and FF of 697 mV, 22.2 mA/cm², and 67%, respectively, after current/light soaking. These advances reduce the barrier for large-scale manufacturing of solution-processed, ultralow-cost solar cells on flexible or curved substrates.

High-performance organic pseudocapacitors via molecular contortion

Pseudocapacitors harness unique charge-storage mechanisms to enable high-capacity, rapidly cycling devices. Here we describe an organic system composed of perylene diimide and hexaazatrinaphthylene exhibiting a specific capacitance of 689 F g^-1 at a rate of 0.5 A g^-1, stability over 50,000 cycles, and unprecedented performance at rates as high as 75 A g^-1. We incorporate the material into two-electrode devices for a practical demonstration of its potential in next-generation energy-storage systems. We identify the source of this exceptionally high rate charge storage as surface-mediated pseudocapacitance, through a combination of spectroscopic, computational and electrochemical measurements. By underscoring the importance of molecular contortion and complementary electronic attributes in the selection of molecular components, these results provide a general strategy for the creation of organic high-performance energy-storage materials.

Doping-Induced Superconductivity in the van der Waals Superatomic Crystal Re6Se8Cl2

Superatomic crystals are composed of discrete modular clusters that emulate the role of atoms in traditional atomic solids. Owing to their unique hierarchical structures, these materials are promising candidates to host exotic phenomena, such as doping-induced superconductivity and magnetism. Low-dimensional superatomic crystals in particular hold great potential as electronic components in nanocircuits, but the impact of doping in such compounds remains unexplored. Here we report the electrical transport properties of Re₆Se₈Cl₂, a two-dimensional superatomic semiconductor. We find that this compound can be n-doped in situ through Cl dissociation, drastically altering the transport behavior from semiconducting to metallic and giving rise to superconductivity with a critical temperature of ∼8 K and upper critical field exceeding 30 T. This work is the first example of superconductivity in a van der Waals superatomic crystal; more broadly, it establishes a new chemical strategy to manipulate the electronic properties of van der Waals materials with labile ligands.

Hierarchical Coherent Phonons in a Superatomic Semiconductor

The coupling of phonons to electrons and other phonons plays a defining role in material properties, such as charge and energy transport, light emission, and superconductivity. In atomic solids, phonons are delocalized over the 3D lattice, in contrast to molecular solids where localized vibrations dominate. Here, a hierarchical semiconductor that expands the phonon space by combining localized 0D modes with delocalized 2D and 3D modes is described. This material consists of superatomic building blocks (Re₆ Se₈ ) covalently linked into 2D sheets that are stacked into a layered van der Waals lattice. Using transient reflectance spectroscopy, three types of coherent phonons are identified: localized 0D breathing modes of isolated superatom, 2D synchronized twisting of superatoms in layers, and 3D acoustic interlayer deformation. These phonons are coupled to the electronic degrees of freedom to varying extents. The presence of local phonon modes in an extended crystal opens the door to controlling material properties from hierarchical phonon engineering.

Modulating the hierarchical fibrous assembly of Au nanoparticles with atomic precision

The ability to modulate nanoparticle (NP) assemblies with atomic precision is still lacking, which hinders us from creating hierarchical NP organizations with desired properties. In this work, a hierarchical fibrous (1D to 3D) assembly of Au NPs (21-gold atom, Au21) is realized and further modulated with atomic precision via site-specific tailoring of the surface hook (composed of four phenyl-containing ligands with a counteranion). Interestingly, tailoring of the associated counterion significantly changes the electrical transport properties of the NP-assembled solids by two orders of magnitude due to the altered configuration of the interacting π-π pairs of the surface hooks. Overall, our success in atomic-level modulation of the hierarchical NP assembly directly evidences how the NP ligands and associated counterions can function to guide the 1D, 2D, and 3D hierarchical self-assembly of NPs in a delicate manner. This work expands nanochemists' skills in rationally programming the hierarchical NP assemblies with controllable structures and properties.

The genomic landscape of diffuse intrinsic pontine glioma and pediatric non-brainstem high-grade glioma

Pediatric high-grade glioma (HGG) is a devastating disease with a two-year survival of less than 20%¹. We analyzed 127 pediatric HGGs, including diffuse intrinsic pontine gliomas (DIPGs) and non-brainstem HGGs (NBS-HGGs) by whole genome, whole exome, and/or transcriptome sequencing. We identified recurrent somatic mutations in ACVR1 exclusively in DIPG (32%), in addition to the previously reported frequent somatic mutations in histone H3, TP53 and ATRX in both DIPG and NBS-HGGs^2-5. Structural variants generating fusion genes were found in 47% of DIPGs and NBS-HGGs, with recurrent fusions involving the neurotrophin receptor genes NTRK1, 2, or 3 in 40% of NBS-HGGs in infants. Mutations targeting receptor tyrosine kinase/RAS/PI3K signaling, histone modification or chromatin remodeling, and cell cycle regulation were found in 68%, 73% and 59%, respectively, of pediatric HGGs, including DIPGs and NBS-HGGs. This comprehensive analysis provides insights into the unique and shared pathways driving pediatric HGG within and outside the brainstem.

Irbesartan-mediated reduction of renal and cardiac damage in insulin resistant JCR : LA-cp rats

BACKGROUND AND PURPOSE

Angiotensin II receptor antagonists (ARBs), originally developed for antihypertensive properties, have pleiotropic effects including direct vascular actions. We tested the hypothesis that the ARB irbesartan would be effective against micro- and macrovascular complications of the prediabetic metabolic syndrome using the obese, insulin-resistant JCR : LA-cp rat that exhibits micro- and macrovascular disease with ischaemic myocardial lesions and renal disease.

EXPERIMENTAL APPROACH

Obese male rats were treated with irbesartan (30 mg.kg(-1).day(-1), incorporated into chow) from 12 to 25 weeks of age.

KEY RESULTS

Irbesartan treatment caused no change in food intake or body weight. Fasting glycaemic control of the JCR : LA-cp rats was marginally improved, at the expense of increased plasma insulin levels ( approximately 50%). Fasting plasma triglycerides were marginally reduced ( approximately 25%), while cholesterol concentrations were unchanged. Elevated concentrations of adiponectin, monocyte chemotactic protein-1 and plasminogen activator inhibitor-1 were reduced along with severity of glomerular sclerosis. Macrovascular dysfunction (aortic hypercontractile response to noradrenergic stimulus and reduced endothelium-dependent relaxation) was improved and frequency of ischaemic myocardial lesions reduced (62%).

CONCLUSIONS AND IMPLICATIONS

Irbesartan reduces markers of inflammation and prothombotic status, improves macrovascular function and reduces glomerular sclerosis and myocardial lesions in a model of the metabolic syndrome. Unlike pharmaceutical agents targeted on metabolic dysfunction, irbesartan reduced end-stage disease without major reduction of plasma lipids or insulin. The protective effects appear to be secondary to unknown intracellular mechanisms, probably involving signal transduction pathways. Understanding these would offer novel pharmaceutical approaches to protection against cardiovascular disease.

Enhanced cell death in MeCP2 null cerebellar granule neurons exposed to excitotoxicity and hypoxia

Rett syndrome (RTT) is associated with mutations in the transcriptional repressor gene MeCP2. Although the clinical and neuropathological signs of RTT suggest disrupted synaptic function, the specific role of methyl-CpG binding protein 2 (MeCP2) in postmitotic neurons remains relatively unknown. We examined whether MeCP2 deficiency in central neurons contributes to the neuropathogenesis in RTT. Primary cerebellar granule neuronal cultures from wild-type (WT) and MeCP2-/- mice were exposed to N-methyl-d-aspartate (NMDA) and AMPA-induced excitotoxicity and hypoxic-ischemic insult. The magnitude of cell death in MeCP2-/- cells after excitotoxicity and hypoxia was greater than in the WT littermate control cultures and occurred after shorter exposures that usually, in the WT, would not cause cell death. Pretreatment with the growth factor fibroblast growth factor 1 (FGF-1) under conditions at which WT cells showed complete neuroprotection, only partially protected MeCP2-/- cells. To elucidate specifically the effects of MeCP2 knockout (KO) on cell death, we examined two death cascade pathways. MeCP2-/- neurons exposed to 6 h of hypoxia exhibited enhanced activation of the proapoptotic caspase-3 and increased mitochondrial release of apoptosis inducing factor (AIF) compared with WT neurons, which did not show significant changes. However, pretreatment with the caspase inhibitor ZVAD-FMK had little or no effect on AIF release and its subcellular translocation to the nucleus, suggesting caspase-independent AIF release and their independent contribution to hypoxia-induced cell death. Reintroduction of intact MeCP2 gene in MeCP2-/- cells or MeCP2 gene silencing by MeCP2siRNA in WT cells further confirmed the differential sensitivity of the WT and MeCP2-/- cells and suggest a direct role of MeCP2 in cell death. These results clearly demonstrate increased cell death occurred in neurons lacking MeCP2 expression via both caspase- and AIF-dependent apoptotic mechanisms. Our findings suggest a novel, yet unknown, role for MeCP2 in central neurons in the control of neuronal response to cell death.

Chylomicron and apoB48 metabolism in the JCR:LA corpulent rat, a model for the metabolic syndrome

Postprandial (PP) lipaemia is a significant contributor to the development of dyslipidaemia and cardiovascular disease (CVD). It is also evident that PP lipaemia is prevalent during conditions of obesity and insulin resistance (IR) and may contribute to increased progression of CVD. Our group has assessed the potential of the obese JCR:LA-cp rat as a model of PP lipaemia in order to explore CM (chylomicron) metabolism during the onset and development of IR in the metabolic syndrome. Studies confirm that both fasting plasma and PP apoB48 (apolipoprotein B48) area under the curve are significantly elevated in the obese JCR:LA-cp phenotype as compared with lean controls. Mechanistic studies have also shown that the concentration of lymphatic CM apoB48 and CM size are significantly increased in this model. Furthermore, PP dyslipidaemia in the obese rat can be improved acutely with supplementation of n-3 polyunsaturated fatty acids. Using a different approach, we have subsequently hypothesized that the vascular remodelling that accompanies IR may explain accelerated entrapment of apoB48-containing particles. Small leucine-rich proteoglycans (including biglycan and decorin) have been observed to co-localize with apoB in human tissue. However, the potential impact of IR on vascular remodelling, particularly in the presence of obesity, remains unclear. Preliminary observations from the JCR:LA-cp model indicate that biglycan protein core content increases with age and is exacerbated by IR, suggestive of pro-atherogenic remodelling. The focus of this review is to contribute to the perspective of PP lipaemia in CVD risk associated with the metabolic syndrome through the use of animal models.

Increased insulin sensitivity and reduced micro and macro vascular disease induced by 2-deoxy-D-glucose during metabolic syndrome in obese JCR: LA-cp rats

BACKGROUND AND PURPOSE

The metabolic syndrome, characterized by obesity, insulin resistance and dyslipidemia, is a major cause of cardiovascular disease. The origins of the syndrome have been hypothesized to lie in continuous availability of energy dense foods in modern societies. In contrast, human physiology has evolved in an environment of sporadic food supply and frequent food deprivation. Intermittent food restriction in rats has previously been shown to lead to reduction of cardiovascular risk and a greater life span. The non-metabolizable glucose analogue, 2-deoxy-D-glucose (2-DG) is taken up by cells and induces pharmacological inhibition of metabolism of glucose. We hypothesized that intermittent inhibition of glucose metabolism, a metabolic deprivation, may mimic intermittent food deprivation and ameliorate metabolic and pathophysiological aspects of the metabolic syndrome.

EXPERIMENTAL APPROACH

Insulin resistant, atherosclerosis-prone JCR:LA-cp rats were treated with 2-DG (0.3% w/w in chow) on an intermittent schedule (2 days treated, one day non-treated, two days treated and two days non-treated) or continuously at a dose to give an equivalent averaged intake.

KEY RESULTS

Intermittent 2-DG-treatment improved insulin sensitivity, which correlated with increased adiponectin concentrations. Further, intermittent treatment (but not continuous treatment) reduced plasma levels of leptin and the inflammatory cytokine IL-1 beta. Both 2-DG treatments reduced micro-vascular glomerular sclerosis, but only the intermittent schedule improved macro-vascular dysfunction.

CONCLUSIONS AND IMPLICATIONS

Our findings are consistent with reduction in severity of the metabolic syndrome and protection against end stage micro- and macro-vascular disease through intermittent metabolic deprivation at a cellular level by inhibition of glucose oxidation with 2-DG.

Impaired postprandial apolipoprotein-B48 metabolism in the obese, insulin-resistant JCR:LA-cp rat: Increased atherogenicity for the metabolic syndrome

AIM

Postprandial lipaemia is a significant contributor to the development of dyslipidaemia and cardiovascular disease, which has more recently been shown as a potential risk factor for obesity and pre-diabetes. Clinically however, the diagnosis of early insulin-resistance remains confounded due to the fact that aberrations in lipid metabolism are not often readily identified using classic indicators of hypercholesterolemia (i.e. LDL).

METHODS

In this study, we assessed the metabolism of apolipoprotein-B48 (apoB48)-containing lipoproteins in an animal model of obesity and insulin-resistance, the JCR:LA-cp rat. The contribution of lipoproteins from the intestine was assessed by measuring plasma apoB48 concentration in the postprandial period following an oral fat load. Plasma apoB48 was measured by improved enhanced chemiluminescent detection and other biochemical parameters measured by established analysis.

RESULTS

Fasting concentrations of plasma apoB48, postprandial apoB48 area under the curve (AUC), as well as incremental-AUC (iAUC), were all significantly greater in the obese phenotype compared to lean controls. Fasting apoB48 correlated significantly with apoB48-iAUC, triglyceride (TG)-iAUC and insulin-iAUC. In addition, there was a highly significant association with fasting insulin and the postprandial ratio of TG:apoB48, a relationship not often detected in humans during insulin-resistance.

CONCLUSIONS/INTERPRETATION

We conclude that the JCR:LA-cp rat can be used as a model of postprandial lipemia to explore chylomicron metabolism during the onset and development of insulin-resistance, including the increased cardiovascular complications of the metabolic syndrome.

Synergistic effects of conjugated linoleic acid and chromium picolinate improve vascular function and renal pathophysiology in the insulin-resistant JCR:LA-cp rat

AIMS

Conjugated linoleic acid (CLA) is a natural constituent of dairy products, specific isomers of which have recently been found to have insulin sensitizing and possible antiobesity actions. Chromium is a micronutrient which, as the picolinate (CrP), has been shown to increase insulin sensitivity in animal models, including the JCR:LA-cp rat. We tested the hypothesis that these agents may have beneficial synergistic effects on the micro- and macrovasculopathy associated with hyperinsulinaemia and early type 2 diabetes.

METHODS

Insulin-resistant cp/cp rats of the JCR:LA-cp strain were treated with mixed isomers of CLA (1.5% w/w in the chow) and/or CrP at 80 microg/kg/day (expressed as Cr) from 4 weeks of age to 12 weeks of age. Plasma insulin, lipid and adiponectin levels, aortic vascular function, renal function and glomerular sclerosis were assessed.

RESULTS

CLA administration reduced food intake, body weight and fasting insulin in JCR:LA-cp rats. Plasma adiponectin levels were significantly elevated in rats treated with both CLA and CrP. Aortic hypercontractility was reduced and the relaxant response to the nitric oxide-releasing agent acetylcholine (Ach) was increased in CrP-treated rats. Striking reductions were also observed in the level of urinary albumin and the severity of glomerular sclerosis in rats treated specifically with CLA.

CONCLUSIONS

CLA and CrP have beneficial effects ameliorating several of the pathophysiologic features of an insulin-resistant rat model. These supplements may be useful adjuncts in the management of patients with the metabolic syndrome and warrant further study.

Insulin-Sensitizing and Cardiovascular Effects of the Sodium-Hydrogen Exchange Inhibitor, Cariporide, in the JCR

The effects of the sodium-hydrogen (Na/H) exchange inhibitor cariporide (HOE642), on insulin sensitivity and vascular function were studied in the JCR:LA-cp rat and the db/db mouse. In the insulin-resistant rat, cariporide reduced fasting insulin levels (42%, P < 0.02) and insulin response in a meal tolerance test (50%, P < 0.01), indicating increased insulin sensitivity. The ACE inhibitor, ramipril, used as a reference agent, reduced the insulin response to the meal, but not fasting levels. The EC50 for acetylcholine-mediated relaxation of phenylephrine-precontracted aortic rings was significantly lower in cariporide-treated rats (P < 0.002), but not in ramipril-treated rats. Flow response of the coronary circulation to bradykinin was significantly greater in both cariporide- and ramipril-treated rats, (3-fold decrease in the EC50, P < 0.05). Cariporide-treated hearts were smaller, slower beating, with greater developed LVP. In the obese db/db mouse, chronic treatment with cariporide obviated vascular hypercontractility and improved endothelial function. Thus, cariporide had beneficial effects on the abnormal insulin metabolism and associated vascular dysfunction in the JCR:LA-cp insulin-resistant rat, which develops advanced cardiovascular disease and ischemic myocardial lesions. It also improved vascular function in a similar mouse model of insulin resistance. These effects were markedly greater than those of ramipril.

A novel complex of arginine-silicate improves micro- and macrovascular function and inhibits glomerular sclerosis in insulin-resistant JCR:LA-cp rats

AIMS/HYPOTHESIS

The metabolic syndrome, with associated vasculopathy, is a major cause of cardiovascular disease and nephropathy. Impaired nitric oxide (NO) metabolism and endothelial function is an important component of the disease process. Increasing the availability of arginine, the precursor of NO, might enhance vascular function and protect against end-stage disease.

MATERIALS AND METHODS

Insulin-resistant JCR:LA-cp rats were treated with arginine-silicate-inositol complex or arginine-HCl at 1.0 g kg(-1) day(-1) (expressed as arginine-HCl) from 8 to 13 weeks of age. The contractile/relaxant function of thoracic aortae and coronary arteries was assessed in vitro. Kidneys were assessed for severity of glomerular sclerosis.

RESULTS

Arginine-silicate complex, but not arginine-HCl, normalised the hypercontractile response of the aorta to phenylephrine via an NO-dependent pathway. Coronary artery function, as indicated by reactive hyperaemia to warm ischaemia, was enhanced by both arginine compounds. In addition, the arginine-silicate complex increased coronary vasodilatation in response to bradykinin. Glomerular sclerosis was significantly reduced in rats treated with the arginine-silicate complex.

CONCLUSIONS/INTERPRETATION

Treatment with exogenous arginine, in an efficiently absorbed form, improves vascular function and reduces nephropathy in an animal model of insulin resistance and cardiovascular disease, via mechanism(s) independent of insulin concentration. Enhancement of NO metabolism through increased availability of the precursor arginine appears to offer protection against micro- and macrovascular disease associated with the metabolic syndrome and insulin resistance.

Leptin and the control of respiratory gene expression in muscle

Leptin plays a central role in the regulation of fatty acid homeostasis, promoting lipid storage in adipose tissue and fatty acid oxidation in peripheral tissues. Loss of leptin signaling leads to accumulation of lipids in muscle and loss of insulin sensitivity secondary to obesity. In this study, we examined the direct and indirect effects of leptin signaling on mitochondrial enzymes including those essential for peripheral fatty acid oxidation. We assessed the impact of leptin using the JCR:LA-cp rat, which lacks functional leptin receptors. The activities of marker mitochondrial enzymes citrate synthase (CS) and cytochrome oxidase (COX) were similar between wild-type (+/?) and corpulent (cp/cp) rats. In contrast, several tissues showed variations in the fatty acid oxidizing enzymes carnitine palmitoyltransferase II (CPT II), long-chain acyl-CoA dehydrogenase (LCAD) and 3-hydroxyacyl-CoA dehydrogenase (HOAD). It was not clear if these changes were due to loss of leptin signaling or to insulin insensitivity. Consequently, we examined the effects of leptin on cultured C(2)C(12) and Sol8 cells. Leptin (3 days at 0, 0.2, or 2.0 nM) had no direct effect on the activities of CS, COX, or fatty acid oxidizing enzymes. Leptin treatment did not affect luciferase-based reporter genes under the control of transcription factors involved in mitochondrial biogenesis (nuclear respiratory factor-1 (NRF-1), nuclear respiratory factor-2 (NRF-2)) or fatty acid enzyme expression (peroxisome proliferator-activated receptors (PPARs)). These studies suggest that leptin exerts only indirect effects on mitochondrial gene expression in muscle, possibly arising from insulin resistance.

Mg2+-dependent ATPase activity in cardiac myofibrils from the insulin-resistant JCR:LA-cp rat

There is a great deal of information presently available documenting a cardiomyopathic condition in insulin-deficient models of diabetes. Less information is available documenting a similar status in non insulin-dependent models of diabetes. We have studied the functional integrity of the myofibrils isolated from hearts of JCR:LA rats. The JCR:LA rat is hyperinsulinemic, hyperlipidemic, glucose intolerant and obese. As such, it carries many of the characteristics found in humans with non insulin-dependent diabetes mellitus. These animals also have many indications of heart disease. However, it is not clear if the hearts suffer from vascular complications or are cardiomyopathic in nature. We examined Mg2+-dependent myofibrillar ATPase in hearts of JCR:LA-cp/cp rats and their corresponding control animals (+/?) and found no significant differences (P> 0.05). This is in striking contrast to the depression in this activity exhibited by cardiac myofibrils isolated from insulin-deficient models of diabetes. Our data demonstrate that myofibrillar functional integrity is normal in JCR:LA-cp rats and suggest that these hearts are not in a cardiomyopathic state. Insulin status may be critical in generating a cardiomyopathic condition in diabetes.

The physiology and clinical applications of vasopressin in critical illness

OBJECTIVE

To present the physiology of vasopressin, and review published data on its use in critically ill patients.

DATA SOURCES

A review of articles on the clinical use of vasopressin in critical care medicine up to 2002 and identified through a MEDLINE search.

SUMMARY OF REVIEW

Vasopressin (antidiuretic hormone) acts via vasopressinergic receptors to maintain osmotic and baroreceptor homeostasis. It has complex and varying effects depending on serum levels, coexisting disease states and organs studied. Synthetic vasopressin is available for clinical use. In large doses (e.g. 40 U) it has vasoconstrictor effects comparable to epinephrine during cardiopulmonary resuscitation. The use of much lower "replacement" doses (e.g. 0.04 U/min) may have a marked vasopressor effect in clinical states associated with vasopressin deficiency; for example sepsis, the organ donor and after cardiopulmonary bypass. These doses are much lower than those leading to cardiovascular effects in healthy patients and may avoid the adverse vasoconstrictor effects seen at "pharmacological" doses. The use of vasopressin to reduce portal pressure and bleeding in oesophageal varices is well established.

CONCLUSIONS

Vasopressin has widespread effects throughout the body and has several important clinical applications in the critically ill patient.

Developmental changes in adipose and muscle lipoprotein lipase activity in the atherosclerosis-prone JCR:LA-corpulent rat

OBJECTIVE

To characterize the developmental changes in adipose and muscle lipoprotein lipase (LPL) activity in the atherosclerosis-prone JCR:LA-corpulent rat, and to test the hypothesis that tissue-specific abnormalities in LPL activity precede the establishment of obesity.

DESIGN

Lean (+/?) and obese cp/cp male JCR:LA rats were studied at 4, 5 and 8 weeks of age, that is at the onset of obesity, and at a time when obesity is well established. Assessment was made of plasma variables related to glucose and lipid metabolism and of LPL activity in several adipose depots, skeletal muscles and the heart.

RESULTS

At week 4, body weights were identical in both genotypes and began to diverge at week 5. Eight-week-old cp/cp rats weighed 35% more than their lean counterparts. Perirenal and epididymal adipose depot weights were also identical in both genotypes at week 4 and began to increase in cp/cp rats at week 5, whereas the subcutaneous depot of 4-week-old cp/cp rats was slightly enlarged. At week 4, the cp/cp rats were hyperinsulinemic (5-fold), hyperleptinemic (30-fold) and hypertriglyceridemic (3-fold) compared to their lean counterparts, and their liver contained twice as much triglyceride. The 4-week-old cp/cp rats displayed 2-7-fold higher LPL specific activity in the various adipose depots compared to lean rats, and enzyme activity remained higher in obese than in lean rats at all subsequent ages. In contrast, LPL activity in the vastus lateralis, gastrocnemius and heart muscles of 4-week-old obese rats was approximately half that observed in lean animals.

CONCLUSION

Profound, persistent alterations in the tissue-specific modulation of LPL activity are established in the JCR:LA cp/cp rat prior to the development of frank obesity. The increase in adipose tissue LPL activity and its decrease in muscle tissues are likely to be related to the concomitant alterations in insulinemia and triglyceridemia, respectively. The pre-obesity, tissue-specific alterations in LPL activity may be considered as an integrated adaptation to increased lipid flux aimed at driving lipids toward storage sites and limiting their uptake by triglyceride-laden muscles.

Increased hepatic VLDL secretion, lipogenesis, and SREBP-1 expression in the corpulent JCR:LA-cp rat

The corpulent JCR:LA-cp rat (cp/cp) is a useful model for study of the metabolic consequences of obesity and hyperinsulinemia. To assess the effect of hyperinsulinemia on VLDL secretion in this model, we measured rates of secretion of VLDL in perfused livers derived from cp/cp rats and their lean littermates. Livers of cp/cp rats secreted significantly greater amounts of VLDL triglyceride and apolipoprotein, compared with lean littermates. The content of apoB, apoE, and apoCs in both perfusate and plasma VLDL was greater in the cp/cp rat, as was the apolipoprotein (apo)C, apoA-I, and apoA-IV content of plasma HDL. Triglyceride content was also greater in cp/cp livers, as was hepatic lipogenesis and expression of lipogenic enzymes and sterol regulatory element binding protein-1 (SREBP-1). Hepatic mRNAs for apoE, and apoA-I were higher in livers of cp/cp rats. In contrast, the steady state levels of apoC-II, apoC-III, and apoB mRNAs were unchanged. Thus, livers of obese hyperinsulinemic cp/cp JCR:LA-cp rats secrete a greater number of VLDL particles that are enriched in triglyceride, apoE, and apoC. Greater secretion of VLDL in the cp/cp rat in part results from higher endogenous fatty acid synthesis, which in turn may occur in response to increased expression of the lipogenic enzyme regulator SREBP-1c.

Reduction and prevention of the cardiovascular sequelae of the insulin resistance syndrome

Insulin resistance and hyperinsulinemia are the critical characteristics of the metabolic syndrome that is associated with abdominal obesity and are the early manifestations of its progression to type 2 diabetes. These metabolic abnormalities are becoming recognized as a major contributor to cardiovascular disease. The experimental studies required to elucidate the underlying mechanisms and to develop effective preventative strategies will require the use of appropriate animal models and these are available. The evidence from such research indicates that a wide range of interventions (including peroxisome proliferator activator receptor agonists, insulin-sensitizing agents, statins, fibrates, angiotensin-converting enzyme inhibitors, estrogen receptor modulators, lipid-based nutriceuticals, and ethanol) can markedly reduce or prevent vasculopathy and ischemic cardiac lesions in animal models. Overall, the results suggest that early damage to the vascular wall, both in function and presenting as atherosclerotic lesions, is secondary to long-term hyperinsulinemia and, especially, to postprandial peaks in plasma insulin levels, and is exacerbated by the accompanying hyperlipidemia. Effective treatment will, of necessity, be preventative and will necessitate diagnostic approaches that can identify asymptomatic individuals at high risk for vascular damage and eventual progression to type 2 diabetes. Therapeutic targets in this population include insulin sensitivity and the associated signal transduction pathways, the peroxisome proliferator activator receptor-alpha and -gamma systems, and the complex pathways leading from acetyl CoA and the citric acid cycle to the synthesis of fatty acid and the storage of triglyceride. These pharmacological approaches offer the prospect of preventing a significant proportion of cardiovascular disease.

Conditioned taste aversion induced by wheel running is not due to novelty of the wheel

Under a within-subjects design, food- and water-restricted rats showed a significant reduction in consumption of a flavor associated with the opportunity to run compared to another flavor associated with a novel wheel without the opportunity to run. Furthermore, there was no evidence that consumption of the flavor paired with the novel wheel differed from a home cage control.

High glucose concentrations induce oxidative damage to mitochondrial DNA in explanted vascular smooth muscle cells

Oxidative stress is considered to be one of the mechanisms leading to atherosclerosis. It occurs in response to injury or to altered metabolic state. Alterations in cell growth (proliferation or apoptosis) can also contribute to the pathogenesis of atherosclerosis and is influenced by oxidative stress. Smooth muscle cells (SMC) from aortic explants of JCR:LA-cp homozygous cp/cp corpulent rats who are genetically predisposed to develop atherosclerosis exhibit increased SMC proliferation, which can be attenuated by exercise and food restriction. This study was conducted to characterize the effects fo oxidative stress and high glucose media on cell growth and its relationship to mitochondrial DNA integrity and gene expression in explanted aortic SMC from corpulent and lean JCR:LA-cp rats. The results show that SMC from the cp/cp rat appear to be resistant to oxidant-induced cell death and that they accumulate mitochondrial DNA mutations, probably as a result of a reduction in apoptosis. These data suggest that susceptibility to age- and glucose-related atherosclerosis may be related to alterations in redox signaling.

Adenocarcinoma of the stomach in an adolescent presenting as pneumoperitoneum: a brief report

BACKGROUND

Adenocarcinoma of the stomach is rare in children and adolescents. A unique case, presenting as an acute abdomen with pneumoperitoneum, is discussed.

METHODS

Case presentation and literature review.

RESULTS

A 13-year-old girl with perforated gastric adenocarcinoma treated by wedge resection developed metastatic disease within two months and died within six months despite chemotherapy.

CONCLUSION

Frozen section of all perforated gastric ulcers, with resection/postoperative chemotherapy for adenocarcinoma.

SUMMARY

A 13-year-old girl with gastric adenocarcinoma presented with pneumoperitoneum. Within two months of wedge resection widespread metastatic disease was documented by computerized tomography scan and laparoscopy and despite chemotherapy, the patient died within six months. Frozen section of all perforated gastric ulcers, even in children, and definitive formal gastrectomy with postoperative chemotherapy, offer the only chance of cure.

Laparoscopic cholecystectomy does not demonstrably decrease survival of patients with serendipitously treated gallbladder cancer

BACKGROUND

The purpose of this study was to evaluate the possibility that laparoscopic cholecystectomy has worsened the prognosis of patients with resected gallbladder cancer; particularly for patients whose cancer was accidentally resected.

STUDY DESIGN

We conducted a retrospective review of Connecticut Tumor Registry data and data extracted from individual patient records at 15 of 30 hospitals in Connecticut reporting data to the Registry, at two separate time points, 1985-1988 (immediate prelaparoscopic era) and 1992-95 (laparoscopic cholecystectomy well established). There were 194 and 208 patients in each 3-year period, respectively. Additional information was extracted from hospital records in 82 and 91 patients, respectively. Twenty-five percent of patients in both data sets presented with "local" or Tis, T1, T2 disease.

RESULTS

Three-year survival for localized disease was 29% in the prelaparoscopic period and 34% once laparoscopic cholecystectomy was established. But analysis of individual patient records indicated that 36% of patients from the laparoscopic period did not actually undergo a laparoscopic procedure. Fifty-nine patients had their gallbladder cancer discovered in the specimen postoperatively (serendipitously treated). A higher proportion of cancers were discovered postoperatively in the laparoscopic era (44% versus 24%). Three-year survival for these patients was 25%. If the data from the two eras are grouped according to whether or not the cancer-bearing gallbladder was manipulated laparoscopically, 24 of 59 patients (41%) turned out to be at risk for the possibility of increased laparoscopic dissemination of tumor. Survival of these patients (11-month median survival) was not statistically different from survival of patients whose serendipitously discovered gallbladder cancer was never manipulated laparoscopically (16-month median survival); p = 0.54 by log rank test.

CONCLUSIONS

The widespread adoption of laparoscopic cholecystectomy did not worsen the survival of patients with gallbladder cancer, and patients with serendipitously treated gallbladder cancers did not have a worse survival after laparoscopic manipulation than after a standard open cholecystectomy. The laparoscopic aspects of operative manipulation of a gallbladder with cancer in it do not appear to be a proximate cause of the poor prognosis in this disease.

Effects of LY117018 and the estrogen analogue, 17alpha-ethinylestradiol, on vascular reactivity, platelet aggregation, and lipid metabolism in the insulin-resistant JCR:LA-cp male rat: role of nitric oxide

The JCR:LA-cp rat is obese and insulin resistant and develops a major vasculopathy, with associated ischemic damage to the heart. Male rats were treated with 17alpha-ethinylestradiol (EE), LY117018, and/or the nitric oxide synthase inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME). LY117018 decreased plasma cholesterol esters, with a 40% reduction in total cholesterol. EE increased triglyceride levels and modestly decreased cholesterol esters. L-NAME increased blood pressure and aortic contractile sensitivity to phenylephrine and inhibited acetylcholine-induced relaxation. LY117018 decreased the force of contraction. The L-NAME-mediated increase in force of contraction and decrease in response to acetylcholine was inhibited by LY117018. L-NAME-induced hypertension was prevented by LY117018. Platelet aggregation was not different between obese and lean rats and was unaffected by L-NAME. LY117018, both in the absence and presence of L-NAME, inhibited platelet aggregation. The effects of LY117018 are apparently mediated through both NO-dependent and -independent mechanisms. The changes induced by EE and LY117018 may reflect the activation of multiple mechanisms, both estrogen receptor-dependent and -independent. The changes induced by LY117018 are significant and may prove to be cardioprotective in the presence of the insulin resistance syndrome.

Beneficial insulin-sensitizing and vascular effects of S15261 in the insulin-resistant JCR:LA-cp rat

S15261, a compound developed for the oral treatment of type II diabetes, is cleaved by esterases to the fragments Y415 and S15511. The aim was to define the insulin-sensitizing effects of S15261, the cleavage products, and troglitazone and metformin in the JCR:LA-cp rat, an animal model of the obesity/insulin resistance syndrome that exhibits an associated vasculopathy and cardiovascular disease. Treatment of the animals from 8 to 12 weeks of age with S15261 or S15511 resulted in reductions in food intake and body weights, whereas Y415 had no effect. Troglitazone caused a small increase in food intake (P <.05). Treatment with S15261 or S15511 decreased plasma insulin levels in fed rats and prevented the postprandial peak in insulin levels in a meal tolerance test. Y415 had no effect on insulin levels. Troglitazone halved the insulin response to the test meal, but metformin gave no improvement. S15261 decreased the expression of phosphoenolpyruvate carboxykinase and glucose-6-phosphatase and stimulated the expression of acetyl-CoA carboxylase and acyl-CoA synthase. S15261 also reduced the expression of carnitine palmitoyltransferase I and hydroxymethyl-glutaryl-CoA synthase. S15261, but not troglitazone, reduced the exaggerated contractile response of mesenteric resistance vessels to norepinephrine, and increased the maximal nitric oxide-mediated relaxation. S15261, through S15511, increased insulin sensitivity, decreased insulin levels, and reduced the vasculopathy of the JCR:LA-cp rat. S15261 may thus offer effective treatment for the insulin resistance syndrome and its associated vascular complications.

Vascular wall function in insulin-resistant JCR:LA-cp rats: role of male and female sex

Vascular wall function was assessed in obese insulin-resistant (cp/cp) and lean normal (+/?), male and female, JCR:LA-cp rats. Both male and female cp/cp rats showed enhanced maximum contractility in response to norepinephrine; impaired smooth muscle in response to sodium nitroprusside, a nitric oxide (NO) donor; and impaired relaxation in response to acetylcholine (ACh), compared with their lean counterparts. The abnormalities were similar in male and female cp/cp rats. The NO synthase inhibitor, Nomega-nitro-L-arginine methyl ester (L-NAME), inhibited ACh-mediated relaxation significantly in male rats, both cp/cp and +/?. The inhibition of ACh-mediated relaxation by L-NAME in +/? females was less, with no reduction in maximal relaxation, and was absent in cp/cp females. These effects suggest that the relative importance of NO in the endothelial modulation of smooth muscle contractility is greater in male rats. The results are consistent with a decreased role for endothelial NO in the cp/cp rats of both sexes and a reduction in NO-independent cholinergic relaxation in the male cp/cp rat. This NO-independent mechanism is not affected in the female cp/cp rats. The relatively small differences between males and females in smooth muscle cell and vascular function may contribute to sex-related differences in the atherogenesis, vasospasm, and ischemic damage associated with the obese insulin-resistant state.

Vascular dysfunction and myocardial contractility in the JCR:LA-corpulent rat

OBJECTIVE

The JCR:LA-corpulent rat is a unique animal model of human vascular disease that exhibits a profound insulin resistance, vasculopathy, and cardiovascular dysfunction. We tested the hypothesis that the defects affect endothelial and smooth muscle function of the coronary microvasculature as well as cardiac contractility. Coronary, myocardial and aortic function were assessed in obese (homozygous for the cp gene, cp/cp) and lean (heterozygous or homozygous normal, +/?) littermates aged 7 and 18 weeks.

METHODS

Coronary endothelial relaxation was examined in isolated perfused hearts by determining the effect of bradykinin (0. 1-1000 nmol l(-1)) on coronary perfusion pressure (CPP), myocardial mechanical function was evaluated in terms of left-ventricular developed pressure (LVDevP), and aortic relaxation with the endothelium-dependent agonist, A 23187 (1-1000 nmol l(-1)).

RESULTS

In rats aged 7 weeks, bradykinin reduced CPP from 133+/-1 mmHg to 43+/-1 mmHg (-67%) in lean rats, but only to 64+/-3 mmHg (-52%) in corpulent rats (n=6, P<0.05). Similar differences were found in rats aged 18 weeks (n=8). Inhibition of NO synthase with N(G)-nitro-L-arginine (L-NNA; 0.2 mmol l(-1)) impaired, and tetrahydrobiopterin (0.1 mmol l(-1)), a NO synthase cofactor, restored relaxation in cp/cp rats. Spermine/NO equally reduced CPP in both groups (-58%). Mechanical function was similar in lean and corpulent rats, aortic endothelial relaxation was attenuated by approximately 30% and aortic smooth muscle function was normal (7 weeks) or improved (18 weeks) in the cp/cp genotype.

CONCLUSION

These results suggest that (i) there is a specific impairment of NO-mediated relaxation of the coronary resistance vessels in the JCR:LA-corpulent rat that is not associated with impaired baseline myocardial contractility, and (ii) exogenous tetrahydrobiopterin reversed the relaxation defects that are part of the vascular complications typical for the insulin resistance syndrome.

Delayed insulin transport across endothelium in insulin-resistant JCR:LA-cp rats

Capillary endothelial cells are thought to limit the transport of insulin across the endothelium, resulting in attenuated insulin action at target sites. Whether endothelial insulin transport is altered in dysglycemic insulin-resistant states is not clear and was therefore investigated in the JCR:LA-cp corpulent male rat, which exhibits the metabolic syndrome of obesity, insulin resistance, hyperlipidemia, and hyperinsulinemia. Lean littermates that did not develop these alterations served as controls. Animals of both groups were normotensive (mean arterial pressure 136+/-2 mmHg). Hearts from obese and lean rats aged 7 (n = 6) or 18 (n = 8) weeks were perfused in vitro at 10 ml/min per gram wet wt over 51 min with Krebs-Henseleit buffer containing 0.1 or 0.5 U human insulin/l (equivalent to 0.6 and 3 nmol/l). Interstitial fluid was collected using a validated method, and interstitial insulin was determined with a radioimmunoassay. At 0.1 U/l, insulin transfer velocity was similar in both experimental groups (half-times of transfer: 11+/-0.2 min in obese and 18+/-4 min in lean rats; NS), but at 0.5 U/l, the respective half-times were 7+/-1 min in lean and 13+/-2 min in obese rats (P < 0.05). The steady-state level of insulin in the interstitium was 34+/-1% of the vascular level at 0.1 U/l and reached the vascular level (102+/-2%) at 0.5 U/l in both lean and obese rats. In rats aged 18 weeks, the half-times of insulin transfer were 31+/-2 and 14+/-l min in obese rats and 10+/-0.3 and 7+/-0.3 min in lean rats (P < 0.05). Again, interstitial steady-state levels were similar in both groups. Finally, postprandial insulin dynamics were simulated over a period of 120 min with a peak concentration of 0.8 U/l in rats aged 27 weeks (n = 4). The maximal interstitial level was 0.38+/-0.02 U/l in lean rats and 0.24+/-0.02 U/l in obese rats (P < 0.05), and a similar difference was noted throughout insulin infusion (areas under the transudate concentration-time curves: 17 and 11 U/min per 1, respectively). These data show, for the first time in a genetic animal model of insulin resistance, that transfer of insulin across the endothelium is substantially delayed in obese insulin-resistant rats and that it likely contributes to the postprandial alterations of glucose metabolism observed in the metabolic syndrome.

Chelation therapy in the JCR:LA-cp rat: experimental assessment of a putative antiatherosclerotic treatment

OBJECTIVE

To test the efficacy of chelation therapy, an alternative medical treatment, as an antiatherosclerotic procedure, using an animal model of insulin resistance and vascular disease.

DESIGN

A prospective animal experiment with procedures modelled on human chelation treatments.

SUBJECTS

The JCR:LA-cp rat, a strain that, if homozygous for the autosomal recessive cp gene, becomes obese and insulin resistant, with marked hyperinsulinemia and hypertriglyceridemia, and is unique in the spontaneous development of atherosclerosis and ischemic myocardial lesions.

EXPERIMENTAL PROTOCOL

Eight-month-old, obese, male JCR:LA-cp rats were fitted with indwelling venous cannulae and infused over 4 weeks with ethylenediaminetetraacetic acid (EDTA) 5 days a week at a daily dose of 40 mg/kg body weight. At the end of the treatment period, samples were taken for assay of blood parameters and for mineral content of bone. The rats were sacrificed and perfusion-fixed for scanning electron microscopy of the aortic arch.

RESULTS

Plasma cholesterol concentrations were not changed by the EDTA treatment. In contrast, plasma triglyceride concentrations were raised significantly (74%, p < 0.05). Lean control rats showed minimal abnormality of the aortic arch, whereas the obese control rats had raised intimal lesions, frequent adherent macrophages and endothelial damage. The frequency of these vascular abnormalities in the EDTA-treated rats was not different from that seen in the obese controls. The bone contents of calcium and magnesium were not significantly reduced.

CONCLUSIONS

Chelation therapy using intravenous EDTA has no beneficial effects on the arterial lesions in the atherosclerotic JCR:LA-cp rat. The increase in plasma triglyceride concentrations would be grounds for concern in human patients.

Bacteria, biofilms, and devices: the possible protective role of phosphorylcholine materials

Phosphorylcholine (PC)-surfaced alloplastic materials improve the biocompatibility of medical devices in contact with blood or tears. Recent experimental studies support the contention that PC surfaces also retard bacterial and crystal adhesion in urine.

Aging and high concentrations of glucose potentiate injury to mitochondrial DNA

Deletions of mitochondrial DNA (mtDNA) are associated with aging and several chronic diseases. We have reported heterogeneous mutations between base pair 8468 and 13446 in mtDNA, the region known as the "common" deletion, in muscle of older humans with impaired glucose tolerance or diabetes mellitus. To further characterize potential effects of age and glycemia on mtDNA integrity, we studied corpulent JCR:LA-cp rats that are characterized by insulin resistance, hyperinsulinemia, and hyperlipidemia, factors strongly associated with both aging and cardiovascular disease. In addition to skeletal muscle, we isolated vascular smooth muscle cells (VSMC) from aortas of 6-, 12-, and 17-month-old rats and exposed them to 5-, 25-, 62-, and 100-mM glucose or a combination of hypoxanthine (100 microM) and xanthine oxidase (0.025 U/ml) to generate reactive oxygen species in separate cultures. Long- and short-fragment and nested polymerase chain reaction was used to detect mutations in the common deletion region. The data demonstrate that aging and the cp genotype confer susceptibility to mtDNA deletions in vivo and that high glucose concentrations can induce mtDNA mutations in vitro. Accordingly, aging and glucose-related oxidative stress and possibly hyperinsulinemia may contribute to alterations in mitochondrial gene integrity and the cp genotype appears to increase the susceptibility of muscle to the age-related accumulation of mtDNA mutations.

Vascular wall dysfunction in JCR:LA-cp rats: effects of age and insulin resistance

We tested the hypothesis that aging and insulin resistance interact to increase vascular dysfunction by comparing the function of isolated mesenteric resistance arteries in obese, insulin-resistant JCR:LA-cp rats and lean, insulin-sensitive rats of the same strain at 3, 6, 9, and 12 mo of age. The peak constrictor responses to norepinephrine, phenylephrine, and high potassium were elevated in arteries from obese rats. Responses to these agents increased with age in both obese and lean rats. An eicosanoid constrictor contributed substantially to vasoconstriction in the arteries from both lean and obese animals. Inhibition of nitric oxide synthase increased the vasoconstrictor response to norepinephrine in both obese and lean rats. This effect increased with age in lean rats only. Vascular relaxation in response to acetylcholine and sodium nitroprusside was impaired in the obese rats and did not alter with age. The results suggest that obese JCR:LA-cp rats have enhanced maximal constriction, which originates in the arterial smooth muscle and increases with age. There is evidence that the ability of the arteries to compensate for the enhanced contractility is impaired in obese rats, particularly with advanced age.

Glucose tolerance and insulin resistance in the JCR:LA-corpulent rat: effect of miglitol (Bay m1099)

A standardized meal tolerance test (MTT) using 5 g rat chow provides a sensitive index of insulin and glucose metabolism in the insulin-resistant, hyperinsulinemic, hypertriglyceridemic, and atherosclerosis-prone JCR:LA-corpulent (cp) strain of rats. The MTT revealed differences in insulin/glucose metabolism that were not evident in either an intravenous (IVGTT) or intraperitoneal (IPGTT) glucose tolerance test. The glycemic response of control rats to a 5-g carbohydrate test meal containing miglitol (Bay m1099) was sharply reduced, with a 50% effective dose (ED50) of 36.4 +/- 7.5 mg/100 g food. At a dose of 60 mg/100 g food, the plasma glucose curve was flat and indistinguishable from that found in the nonfed state. The plasma insulin response was similarly reduced, with an ED50 of 42.8 +/- 14.8 mg/100 g food. Obese male rats were treated with miglitol at 60 mg/100 g food from 6 to 12 weeks of age. Treated rats had a significantly reduced food consumption and lower body weight at 12 weeks of age (P < .05). The treatment resulted in no significant changes in serum lipid concentrations. When subjected to the MTT using control (non-miglitol-containing) food, treated rats demonstrated markedly improved insulin sensitivity, with a greatly reduced insulin response, which may reflect an improved hepatic glucose metabolism. The results confirm that miglitol is highly effective in this obese insulin-resistant animal model. It reduced postprandial glycemic and insulin responses, and on long-term treatment, it improved glucose and insulin metabolism. These beneficial metabolic changes suggest that miglitol may have vascular protective effects in insulin-resistant states.

One hospital's successful 20-year experience with physician assistants in graduate medical education

The downsizing of residencies and the migration of residents to outpatient settings create an increasing need to protect residents' educational experiences and to maintain standards of hospital care. Some hospitals have solved this dilemma by using mid-level practitioners (MLPs), including physician assistants (PAs), to augment the diminished staffs of residents in their surgical residencies. The authors describe how their hospital has done so. Their surgical PA program, begun in 1979, seeks to meet the hospital's expectations for in-house coverage of surgical patients, to protect the educational integrity of the physician residency program in surgery, to allow protected time for residents' conferences and clinics, and to prepare residents for future practice in multidisciplinary teams. The PA and residents' services are partly separated, which reduces the potential for resident-PA conflict. Responsibilities for both residents and PAs are stratified (junior vs senior status). Both services are teaching services, which helps motivate PAs to be committed to the service and helps foster the equality between residents and PAs that the program strives for. The residents have come to value the PAs, and the program's goals have been achieved, including protecting time for residents' education and maintaining humane on-call schedules for residents. The authors discuss job satisfaction, turnover, and the hard financial realities of paying for PAs' salaries, benefits, and educational programs, as well as the loss of Medicare DME and IME reimbursements when a PA replaces a resident. Ways some of these costs can be recovered are outlined. The authors conclude with recommendations on how to deal with six key issues of PA or other MLP programs: need for institutional commitment; importance of local circumstances; emphasis on partnership, not competition, between PAs and residents; value of an education component; need to build a cohesive program, and the importance of effective PA leadership.

Cardiac myofibrillar and sarcoplasmic reticulum function are not depressed in insulin-resistant JCR:LA-cp rats

Depressed myofibrillar Ca2+-ATPase activity and sarcoplasmic reticulum (SR) Ca2+ uptake are important mechanisms that are responsible for the cardiac dysfunction exhibited by insulin-deficient (type I) diabetic animals. The JCR:LA-cp rat is a model for type II non-insulin-dependent diabetes mellitus (NIDDM). This rat is insulin resistant, obese, and has high levels of circulating glucose, cholesterol, insulin, and triglycerides. The purpose of this study was to determine whether changes in cardiac myofibrillar, SR, and cardiomyocyte function exist in this model of type II diabetes. Myofibrils and SR were isolated from hearts by differential centrifugation. Surprisingly, we found that myofibrillar Ca2+-ATPase activities were unaltered in these animals. Ca2+ uptake in isolated SR fractions was increased in diabetic cp/cp rats, whereas Ca2+-ATPase activity and ryanodine binding were unchanged. Cardiomyocytes isolated from hearts of control and experimental animals had similar active cell shortening and intracellular Ca2+ concentration under basal conditions and in response to caffeine. Our data argue against the presence of a cardiomyopathy in this diabetic model and suggest that insulin may be an important factor in the cardiomyopathy observed in type I diabetic models.