Autophagy in human type 2 diabetes pancreatic beta cells.

AIMS/HYPOTHESIS: Beta cell loss contributes to type 2 diabetes, with increased apoptosis representing an underlying mechanism. Autophagy, i.e. the physiological degradation of damaged organelles and proteins, may, if altered, be associated with a distinct form of cell death. We studied several features of autophagy in beta cells from type 2 diabetic patients and assessed the role of metabolic perturbation and pharmacological intervention. METHODS: Pancreatic samples were obtained from organ donors and isolated islets prepared both by collagenase digestion and density gradient centrifugation. Beta cell morphology and morphometry were studied by electron microscopy. Gene expression studies were performed by quantitative RT-PCR. RESULTS: Using electron microscopy, we observed more dead beta cells in diabetic (2.24 +/- 0.53%) than control (0.66 +/- 0.52%) samples (p < 0.01). Massive vacuole overload (suggesting altered autophagy) was associated with 1.18 +/- 0.54% dead beta cells in type 2 diabetic samples and with 0.36 +/- 0.26% in control samples (p < 0.05). Density volume of autophagic vacuoles and autophagosomes was significantly higher in diabetic beta cells. Unchanged gene expression of beclin-1 and ATG1 (also known as ULK1), and reduced transcription of LAMP2 and cathepsin B and D was observed in type 2 diabetic islets. Exposure of non-diabetic islets to increased NEFA concentration led to a marked increase of vacuole accumulation, together with enhanced beta cell death, which was associated with decreased LAMP2 expression. Metformin ameliorated autophagy alterations in diabetic beta cells and beta cells exposed to NEFA, a process associated with normalisation of LAMP2 expression. CONCLUSIONS/INTERPRETATION: Beta cells in human type 2 diabetes have signs of altered autophagy, which may contribute to loss of beta cell mass. To preserve beta cell mass in diabetic patients, it may be necessary to target multiple cell-death pathways.

Insulin secretion defects of human type 2 diabetic islets are corrected in vitro by a new reactive oxygen species scavenger.

Oxidative stress is a putative mechanism leading to beta-cell damage in type 2 diabetes. We studied isolated human pancreatic islets from type 2 diabetic and non-diabetic subjects, matched for age and body mass index. Evidence of increased oxidative stress in diabetic islets was demonstrated by measuring nitrotyrosine concentration and by electron paramagnetic resonance. This was accompanied by reduced glucose-stimulated insulin secretion, as compared to non-diabetic islets (Stimulation Index, SI: 0.9 +/- 0.2 vs. 2.0 +/- 0.4, P<0.01), and by altered expression of insulin (approximately -60%), catalase (approximately +90%) and glutathione peroxidase (approximately +140%). When type 2 diabetic islets were pre-exposed for 24 h to the new antioxidant bis(1-hydroxy-2,2,6,6-tetramethyl-4-piperidinyl)decandioate di-hydrochloride, nitrotyrosine levels, glucose-stimulated insulin secretion (SI: 1.6+/-0.5) and gene expressions improved/normalized. These results support the concept that oxidative stress may play a role in type 2 diabetes beta-cell dysfunction; furthermore, it is proposed that therapy with antioxidants could be an interesting adjunctive pharmacological approach to the treatment of type 2 diabetes.

Acute aortic dissection in the young: clinical series.

Acute aortic dissection (AAD) is an uncommon lethal cardiovascular emergency demanding prompt diagnosis and aggressive therapeutic intervention. Although it usually affects males over 60 years of age, it may also occur in young adults with specific risk factors such as Marfan syndrome, bicuspid aortic valve and larger aortic dimensions. Moreover, it should be underlined that it is frequently associated with unusual presentation and that the mortality risk is similar to older AAD patients. Thus ''a call to arms'' of the medical community is needed to better understand the spectrum of acute aortic syndromes and to define appropriate diagnostic and therapeutic pathways. We report a series of 6 young patients with type A - AAD referred over the past years at our institute.

Effects of antilipolytic agents on rat liver peroxisomes and peroxisomal oxidative activities.

The mechanisms involved in the inhibitory effects of antilipolytic agents on rat liver peroxisomal fatty acid oxidative activity have been explored. Treatment of fasting rats with antilipolytic drugs (either 3,5-dimethylpyrazole (12 mg/kg body weight) or Acipimox (25 mg/kg body weight] resulted in a decrease in free fatty acid and glucose plasma levels within 5-10 and in a significant increase in the plasma glucagon to insulin ratio within 15. Changes in the fatty acid oxidative activity appeared with a 2.5-3 h delay and were then very rapid (a 30-40% decrease in the activity occurred in additional 2 h). Many peroxisomal enzyme activities (including non-beta-oxidative activities such as uricase and D-amino acid oxidase) exhibited similar changes with the same delay. Simultaneously with the enzyme changes, at the electron microscope level many autophagic vacuoles were detected in the liver cells, often containing peroxisomal structures. Glutamine, an inhibitor of proteolysis in vivo, prevented the decrease in enzyme activities. It was concluded that the decrease in peroxisomal enzyme activities may be the consequence of enhanced peroxisome degradation due to the stimulation of autophagic processes in liver cells.

Massive isolation, morphological and functional characterization, and xenotransplantation of bovine pancreatic islets.

The limited availability of human donors makes the search for alternative islet sources mandatory for future developments in pancreatic islet transplantation. In this study, we report on the massive isolation of bovine islets of proven in vitro and in vivo viability. The islets were prepared by collagenase digestion, sequential filtrations, and density-gradient purification by modifying a technique previously developed in our laboratory for the porcine pancreas. The prepurification yield was 2,743 +/- 78 islet equivalents (IE)/g pancreas (mean +/- SE), with a postpurification recovery of 78.7 +/- 2.2%. Purity ranged from 80 to 90%. The histological and immunocytochemical studies demonstrated the identity and integrity of the islets with well-preserved insulin-, glucagon-, and somatostatin-containing cells. The morphological integrity of cultured bovine islets was demonstrated for up to 4 weeks from isolation. Insulin secretion from freshly isolated islets was similar at 3.3 mmol/l glucose (0.36 +/- 0.06 pmol.IE-1.min-1) and at 14 mmol/l glucose (0.42 +/- 0.00 pmol.IE-1.min-1), and it increased significantly (P < 0.01) at 25 mmol/l glucose (1.44 +/- 0.12 pmol.IE-1.min-1). Arginine, theophylline, and propionic acid increased insulin secretion from freshly isolated islets at 3.3 and 14 mmol/l glucose, but not at 25 mmol/l glucose. Islets cultured at 37 degrees C in CMRL 1066 culture medium for at least 10 days were shown to become responsive to a lower glucose concentration, as demonstrated by the significant increase of insulin release in response to 14 mmol/l glucose, when compared with basal secretion. This recovered responsivity to glucose was maintained after 4 weeks of culture.(ABSTRACT TRUNCATED AT 250 WORDS)

A role for hormone-sensitive lipase in glucose-stimulated insulin secretion: a study in hormone-sensitive lipase-deficient mice.

Endogenous lipid stores are thought to be involved in the mechanism whereby the beta-cell adapts its secretory capacity in obesity and diabetes. In addition, hormone-sensitive lipase (HSL) is expressed in beta-cells and may provide fatty acids necessary for the generation of coupling factors linking glucose metabolism to insulin release. We have recently created HSL-deficient mice that were used to directly assess the role of HSL in insulin secretion and action. HSL(-/-) mice were normoglycemic and normoinsulinemic under basal conditions, but showed an approximately 30% reduction of circulating free fatty acids (FFAs) with respect to control and heterozygous animals after an overnight fast. An intraperitoneal glucose tolerance test revealed that HSL-null mice were glucose-intolerant and displayed a lack of a rise in plasma insulin after a glucose challenge. Examination of plasma glucose during an insulin tolerance test suggested that HSL-null mice were insulin-resistant, because plasma glucose was barely lowered after the injection of insulin. Freshly isolated islets from HSL-deficient mice displayed elevated secretion at low (3 mmol/l) glucose, failed to release insulin in response to high (20 mmol/l) glucose, but had a normal secretion when challenged with elevated KCl. The phenotype of heterozygous mice with respect to the measured parameters in vitro was similar to that of wild type. Finally, the islet triglyceride content of HSL(-/-) mice was 2-2.5 fold that in HSL(-/+) and HSL(+/+) animals. The results demonstrate an important role of HSL and endogenous beta-cell lipolysis in the coupling mechanism of glucose-stimulated insulin secretion. The data also provide direct support for the concept that some lipid molecule(s), such as FFAs, fatty acyl-CoA or their derivatives, are implicated in beta-cell glucose signaling.

Experimental NIDDM: development of a new model in adult rats administered streptozotocin and nicotinamide.

We took advantage of the partial protection exerted by suitable dosages of nicotinamide against the beta-cytotoxic effect of streptozotocin (STZ) to create a new experimental diabetic syndrome in adult rats that appears closer to NIDDM than other available animal models with regard to insulin responsiveness to glucose and sulfonylureas. Among the various dosages of nicotinamide tested in 3-month-old Wistar rats (100-350 mg/kg body wt), the dosage of 230 mg/kg, given intraperitoneally 15 min before STZ administration (65 mg/kg i.v.) yielded a maximum of animals with moderate and stable nonfasting hyperglycemia (155 +/- 3 vs. 121 +/- 3 mg/dl in controls; P < 0.05) and 40% preservation of pancreatic insulin stores. We also evaluated beta-cell function both in vitro and in vivo 4-9 weeks after inducing diabetes. In the isolated perfused pancreas, insulin response to glucose elevation (5-11 mmol/l) was clearly present, although significantly reduced with respect to controls (P < 0.01). Moreover, the insulin response to tolbutamide (0.19 mmol/l) was similar to that observed in normal pancreases. Perfused pancreases from diabetic animals also exhibited a striking hypersensitivity to arginine infusion (7 mmol/l). In rats administered STZ plus nicotinamide, intravenous glucose tolerance tests revealed clear abnormalities in glucose tolerance and insulin responsiveness, which were interestingly reversed by tolbutamide administration (40 mg/kg i.v.). In conclusion, this novel NIDDM syndrome with reduced pancreatic insulin stores, which is similar to human NIDDM in that it has a significant response to glucose (although abnormal in kinetics) and preserved sensitivity to tolbutamide, may provide a particularly advantageous tool for pharmacological investigations of new insulinotropic agents.

Age-dependent changes in the sensitivity of the rat to a diabetogenic agent (streptozotocin).

Changes of plasma glucose levels have been investigated in rats of 50, 70, 90, 110 and 150 g BW after the intravenous injection of 0, 40, 60, 80 or 100 mg/kg BW of streptozotocin. The effect of streptozotocin was dependent on the dose used and on the size of the animals. With all animal sizes studied, a transient acute hyperglycemic response to streptozotocin was observed at doses lower than those required to produce persistent hyperglycemia. Smaller animals required higher doses of streptozotocin in order to produce changes comparable to those observed in larger animals.

Stimulation of insulin release by glucose in a transplantable rat islet cell tumor.

A subline of an x-ray-induced transplantable rat insulinoma has been studied in vivo and in vitro. Tumors grew rapidly after sc transplantation and were rich in insulin, but contained only small amounts of glucagon and somatostatin. Despite marked basal hyperinsulinemia, iv glucose administration caused a further increase in plasma insulin in tumor-bearing rats. When the pancreas was functionally excluded by ligation of supplying arteries, glucose still elicited a clear insulin response. In vitro, insulin release from perifused tumor fragments was stimulated by the combination of glucose and 3-isobutyl-1-methylxanthine, but not by glucose alone. In contrast, there was a clear stimulation of insulin release by glucose in primary monolayer cultures of tumor cells. This suggests a better functional capacity of the cultured cells compared to that of the tumor fragments. The results indicate that this transplantable rat islet cell tumor is a convenient source of large quantities of functional beta-cells.

Mechanisms involved in the effect of nitric oxide synthase inhibition on L-arginine-induced insulin secretion.

1. A constitutive nitric oxide synthase (NOSc) pathway negatively controls L-arginine-stimulated insulin release by pancreatic beta cells. We investigated the effect of glucose on this mechanism and whether it could be accounted for by nitric oxide production. 2. NOSc was inhibited by N omega-nitro-L-arginine methyl ester (L-NAME), and sodium nitroprusside (SNP) was used as a palliative NO donor to test whether the effects of L-NAME resulted from decreased NO production. 3. In the rat isolated perfused pancreas, L-NAME (5 mM) strongly potentiated L-arginine (5 mM)-induced insulin secretion at 5 mM glucose, but L-arginine and L-NAME exerted only additive effects at 8.3 mM glucose. At 11 mM glucose, L-NAME significantly inhibited L-arginine-induced insulin secretion. Similar data were obtained in rat isolated islets. 4. At high concentrations (3 and 300 microM), SNP increased the potentiation of arginine-induced insulin output by L-NAME, but not at lower concentrations (3 or 30 nM). 5. L-Arginine (5 mM) and L-ornithine (5 mM) in the presence of 5 mM glucose induced monophasic beta cell responses which were both significantly reduced by SNP at 3 nM but not at 30 nM; in contrast, the L-ornithine effect was significantly increased by SNP at 3 microM. 6. Simultaneous treatment with L-ornithine and L-arginine provoked a biphasic insulin response. 7. At 5 mM glucose, L-NAME (5 mM) did not affect the L-ornithine secretory effect, but the amino acid strongly potentiated the alteration by L-NAME of L-arginine-induced insulin secretion. 8. L-Citrulline (5 mM) significantly reduced the second phase of the insulin response to L-NAME (5 mM) + L-arginine (5 mM) and to L-NAME + L-arginine + SNP 3 microM. 9. The intermediate in NO biosynthesis, NG-hydroxy-L-arginine (150-300 microM) strongly counteracted the potentiation by L-NAME of the secretory effect of L-arginine at 5 mM glucose. 10. We conclude that the potentiation of L-arginine-induced insulin secretion resulting from the blockade of NOSc activity in the presence of a basal glucose concentration (1) is strongly modulated by higher glucose concentrations, (2) is not due to decreased NO production but (3) is probably accounted for by decreased levels of NG-hydroxy-L-arginine or L-citrulline, resulting in the attenuation of an inhibitory effect on arginase activity.

Insufficient adaptive capability of pancreatic endocrine function in dexamethasone-treated ageing rats.

This study was aimed at exploring the capability of the pancreatic endocrine adaptive mechanisms of ageing Sprague-Dawley rats to counteract the metabolic challenge induced by the prolonged administration of dexamethasone (DEX) (0.13 mg/kg per day for 13 days). DEX treatment induced peripheral insulin resistance in 3-, 18- and 26-month-old rats, as indicated by the significant and persistent rise of plasma insulin levels in each age group (plasma insulin in 3-, 18- and 26-month-old rats from basal values of 4.3+/-0.8, 4.7+/-0.5 and 5.6+/-1.0 ng/ml (means+/-s.e.m.) respectively, rose to 11.9+/-1.7, 29.1+/-5.5 and 27.9+/-2.7 ng/ml respectively, after 9 days of administration). However, plasma glucose concentrations remained unchanged during the treatment in young rats, whereas they increased up to frankly diabetic levels in most 18-month-old and in all 26-month-old animals after a few days of DEX administration. Plasma free fatty acid concentrations increased 2-fold in 3- and 26-month-old rats and 4-fold in 18-month-old rats and could possibly be involved in the glucocorticoid-induced enhancement in insulin resistance, although they showed no significant correlation with glycaemic values. Incubation of pancreatic islets obtained from treated rats showed that DEX administration increased the insulin responsiveness of islets from not only younger but also older donors. However, in the islets of ageing rats, which already showed an age-dependent impairment of the sensitivity to glucose and other secretagogues, this enhancing effect was clearly attenuated with respect to the younger counterpart. Furthermore, DEX treatment depressed significantly the priming effect of glucose in islets isolated from all the three age groups. In conclusion, our results show that ageing rats are unable to counteract effectively a prolonged hyperglycaemic challenge as such induced by DEX administration. This homeostatic defect can be ascribed to the age-dependent failure of the endocrine pancreas to provide enough insulin to overcome the aggravation of an antecedent state of increased peripheral insulin resistance.

Age-dependent reduction in GLUT-2 levels is correlated with the impairment of the insulin secretory response in isolated islets of Sprague-Dawley rats.

In this study we have investigated the insulin secretory response to glucose and other secretagogues (2-ketoisocaproate, 3-isobutyl-1-methyl-xanthine and arginine) of pancreatic islets isolated from Sprague-Dawley rats of various ages (from 2 to 28 months). Our results showed a significant decline in the glucose-stimulated insulin secretion, starting at 12 months of age. On the other hand, the response to non-glucose secretagogues (and mainly to 2-ketoisocaproate) was less impaired with advancing age than that to glucose. We also observed a progressive age-related decline of protein levels of the glucose transporter GLUT-2 in pancreatic islets, which was temporally concomitant and quantitatively comparable with the beta-cell alteration in glucose responsiveness (-40/50%). Finally, we observed a significant increase of the islets insulin content in older rats with respect to younger animals. We conclude that in the islet of older rats the impaired capability to respond to glucose could be dependent, at least in part, on the age-dependent reduction in GLUT-2 and could be compensated by mechanisms including a preserved responsiveness to non-glucose secretagogues and/or the development of islet hypertrophy.

Metabolic and functional studies on isolated islets in a new rat model of type 2 diabetes.

In a new experimental type 2 diabetic syndrome, a 40% reduction of pancreatic beta cells was observed by morphometric analysis. In diabetic islets, as compared to control islets, insulin release was decreased in response to high glucose but not to other stimuli, and total glucose oxidation and utilization were unchanged or slightly reduced. The extent of metabolic and functional impairment appeared proportional to the beta-cell loss. However, a substantial decrease was found in protein level and activity (by 77 and 60%, respectively, versus controls) of mitochondrial FAD-glycerophosphate dehydrogenase (mGDH), the key enzyme of the glycerophosphate shuttle. Interestingly, in diabetic islets, as recently reported for mGDH-deficient transgenic mice, definite functional alterations (mainly in response to D-glyceraldehyde) were only obtained upon pharmacological blockade of the second shuttle (i.e. malate-aspartate) responsible for mitochondrial transfer of reducing equivalents. In conclusion, in this diabetes model with reduction of beta-cell mass, the islets, despite decreased mGDH amount and activity, appear metabolically and functionally active in vitro, likely through the intervention of adaptive mechanisms, yet prone to failure in challenging situations.

Alteration of beta-cell constitutive NO synthase activity is involved in the abnormal insulin response to arginine in a new rat model of type 2 diabetes.

We have previously obtained a new type 2 diabetic syndrome in adult rats given streptozotocin and nicotinamide, characterized by reduced beta-cell mass, partially preserved insulin response to glucose and tolbutamide and excessive responsiveness to arginine. We have also established that the neuronal isoform of constitutive NO synthase (nNOS) is expressed in beta-cells and modulates insulin secretion. In this study, we explored the kinetics of glucose- and arginine-stimulated insulin release in perifused isolated islets as well as the effect of N-omega-nitro-L-arginine methyl ester (L-NAME), a NOS inhibitor, to get insight into the possible mechanisms responsible for the arginine hypersensitivity observed in vitro in this and other models of type 2 diabetes. A reduced first phase and a blunted second phase of insulin secretion were observed upon glucose stimulation of diabetic islets, confirming previous data in the isolated perfused rat pancreas. Exposure of diabetic islets to 10 mM arginine, in the presence of 2.8 mM glucose, elicited a remarkable monophasic increment in insulin release, which peaked at 639 +/- 31 pg/islet/min as compared to 49 +/- 18 pg/islet/min in control islets (P << 0.01). The addition of L-NAME to control islets markedly enhanced the insulin response to arginine, as expected from the documented inhibitory effect exerted by nNOS activity in normal beta-cells, whereas it did not further modify the insulin secretion in diabetic islets, thus implying the occurrence of a defective nNOS activity in these islets. A reduced expression of nNOS mRNA was found in the majority but not in all diabetic islet preparations and therefore cannot totally account for the absence of L-NAME effect, that might also be ascribed to post-transcriptional mechanisms impairing nNOS catalytic activity. In conclusion, our results provide for the first time evidence that functional abnormalities of type 2 experimental diabetes, such as the insulin hyper-responsiveness to arginine, could be due to an impairment of nNOS expression and/or activity in beta-cells.

A constitutive nitric oxide synthase modulates insulin secretion in the INS-1 cell line.

We provide immunocytochemical evidence that the neuronal isoform of constitutive NO synthase (cNOS) is expressed in the rat insulinoma cell line INS-1. Furthermore, using N omega-nitro-L-arginine methyl ester (L-NAME), a pharmacological inhibitor of cNOS activity, we show that this enzyme is implicated in the modulation of insulin secretion in INS-1 cells. Indeed, in the presence of 2.8 mM glucose, L-NAME induced a specific and dose-dependent increase in insulin release, suggesting that cNOS exerts an inhibitory tone on basal insulin secretion. Moreover, L-arginine, the physiological substrate of cNOS, significantly reduced the marked enhancing effect of L-NAME on insulin release and to a lesser extent, at low concentrations, that of 10 mM KCl. L-NAME also potentiated the insulin secretion stimulated by 5.5 and 8.3 mM glucose, but in this case, its effect was not reduced by L-arginine. In conclusion, our data show that the neuronal isoform of cNOS exerts a negative modulation on insulin secretion in INS-1 cells, confirming the previous results obtained in the isolated perfused rat pancreas or pancreatic islets.

Dexamethasone-induced insulin resistance and pancreatic adaptive response in aging rats are not modified by oral vanadyl sulfate treatment.

OBJECTIVE: To explore the adaptive response of the endocrine pancreas in vivo and in vitro and the possible beneficial effect of the insulino-mimetic agent vanadyl sulfate (VOSO(4)), using glucocorticoid treatment to increase insulin resistance, in aging rats. DESIGN AND METHODS: Dexamethasone (Dex) (0.13 mg/kg b.w.) was administered daily for 13 days to 3- and 18-month old Sprague-Dawley rats and oral VOSO(4) was given from the 5th day. Plasma glucose, insulin and free fatty acids (FFA) concentrations were measured during these treatments and the insulin secretory response of the isolated perfused pancreas was assessed at the end of the experiment. RESULTS AND CONCLUSIONS: In both young and aging rats, particularly in the latter, hyperinsulinemia and increased in vitro insulin responsiveness to glucose were observed in response to Dex treatment, concomitant with an increase in plasma FFA concentrations. Thus, in glucocorticoid-treated animals, the beta-cell adaptive response occurred in both age groups and could possibly be mediated by increased circulating FFA; however, it was insufficient to prevent hyperglycemia in 60% of aging animals. Oral VOSO(4) administration failed to correct Dex-induced alterations in glucose and lipid metabolism, although it influenced in vitro beta-cell responsiveness to stimuli in aging rats.

Protein glycation in the aging male Sprague-Dawley rat: effects of antiaging diet restrictions.

Protein glycation and accumulation of advanced glycosylated end-products (AGEs) are supposed to play an important role in the process of aging. Dietary restriction increases life span and delays the onset of most age-associated diseases. Age-dependent changes in glucose homeostasis and glycated plasma proteins and hemoglobin were determined, and AGEs formation was measured as fluorescence in skin and aortic collagens in male Sprague-Dawley rats fed ad libitum or subjected to every-other-day feeding or 40% food restriction. In aging control rats, skin and aortic collagen-linked fluorescence increased with a similar exponential curve (aortic value being always higher), whereas glycated plasma protein and hemoglobin decreased slightly. Dietary restrictions decreased glycated plasma proteins and fluorescent products in skin collagen of younger but not older rats, and did not affect glycated hemoglobin or aortic collagen fluorescence. In conclusion, our data indicate that age-related changes in glucose homeostasis do not play a substantial role in aging; and collagen-linked fluorescence increases significantly during aging, but it may not be sensitive to dietary intervention.

The antilipolytic agent 3,5-dimethylpyrazole inhibits insulin release in response to both nutrient secretagogues and cyclic adenosine monophosphate agonists in isolated rat islets.

This study intended to test the hypothesis that intracellular lipolysis in the pancreatic beta cells is implicated in the regulation of insulin secretion stimulated by nutrient secretagogues or cyclic adenosine monophosphate (cAMP) agonists. Indeed, although lipid signaling molecules were repeatedly reported to influence beta-cell function, the contribution of intracellular triglycerides to the generation of these molecules has remained elusive. Thus, we have studied insulin secretion of isolated rat pancreatic islets in response to various secretagogues in the presence or absence of 3,5-dimethylpyrazole (DMP), a water-soluble and highly effective antilipolytic agent, as previously shown in vivo. In vitro exposure of islets to DMP resulted in an inhibition (by approximately 50%) of the insulin release stimulated not only by high glucose, but also by another nutrient secretagogue, 2-ketoisocaproate, as well as the cAMP agonists 3-isobutyl-1-methylxanthine and glucagon. The inhibitory effect of DMP, which was not due to alteration of islet glucose oxidation, could be reversed upon addition of sn-1,2-dioctanoylglycerol, a synthetic diglyceride, which activates protein kinase C. The results provide direct pharmacologic evidence supporting the concept that endogenous beta-cell lipolysis plays an important role in the generation of lipid signaling molecules involved in the control of insulin secretion in response to both fuel stimuli and cAMP agonists.

Isolated atrial inversion in situs inversus: a rare anatomic arrangement.

Isolated atrial inversion in situs inversus is a rare congenital cardiac malformation. Its physiology resembles transposition of great vessels, and the best option for its surgical treatment is the atrial switch operation. In this article, we present a case of isolated atrial inversion in concordance with visceral situs inversus diagnosed at birth by echocardiography and cardiac catheterization, which was successfully treated at 8 months of age by a Senning procedure.

Type B aortic dissection involving an isolated right-sided aortic arch.

We report a case of a 48-year-old man in whom type B aortic dissection in the right aortic arch and right descending aorta was diagnosed by transesophageal echocardiography and computed tomographic scan. Angiography was necessary to define the anatomy of the branching vessels. The patient was successfully treated by interposition of a Vascutek 24-mm Dacron woven tube with a right posterolateral thoracotomy approach. Circulatory arrest in profound hypothermia and cerebral retroperfusion were used.