Changes in the content and structure of the coenzyme A moiety in the liver of diabetic mice (db/db) administered a regimen of nicotinamide

Alterations in the content and structure of CoA moiety typical of hyperlipogenesis (a rise in total and free CoA levels, a drop in short-chained fatty acyl-CoA/CoA and long-chained fatty acyl-CoA/CoA ratios) were found in the liver of obese mice with non-insulin-dependent diabetes (db/db). The treatment of diabetic mice with nicotinamide, an antilipemic drug, was accompanied by a decrease in total and free CoA levels and a rise in short-chained fatty acyl-CoA content and short-chained fatty acyl-CoA/CoA and long-chained fatty acyl-CoA/CoA ratios, probably leading to the inhibition of the enzymes of primary lipogenesis steps. It is suggested that CoA moiety structure is essential as an integral index regulating the rate of fatty acid biosynthesis in diabetes mellitus.     

Activation of PPARdelta alters lipid metabolism in db/db mice

Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors, which heterodimerize with the retinoid X receptor and bind to peroxisome proliferator response elements in the promoters of regulated genes. Despite the wealth of information available on the function of PPARalpha and PPARgamma, relatively little is known about the most widely expressed PPAR subtype, PPARdelta. Here we show that treatment of insulin resistant db/db mice with the PPARdelta agonist L-165041, at doses that had no effect on either glucose or triglycerides, raised total plasma cholesterol concentrations. The increased cholesterol was primarily associated with high density lipoprotein (HDL) particles, as shown by fast protein liquid chromatography analysis. These data were corroborated by the chemical analysis of the lipoproteins isolated by ultracentrifugation, demonstrating that treatment with L-165041 produced an increase in circulating HDL without major changes in very low or low density lipoproteins. White adipose tissue lipoprotein lipase activity was reduced following treatment with the PPARdelta ligand, but was increased by a PPARgamma agonist. These data suggest both that PPARdelta is involved in the regulation of cholesterol metabolism in db/db mice and that PPARdelta ligands could potentially have therapeutic value.     

Oleoyl-estrone lowers the body weight of both ob/ob and db/db mice.

Homozygous obese db/db (BKS-Lepr(db) and ob/ob (B6-Lep(ob)) mice were treated for 14 days with a continuous infusion of a fat emulsion (controls) or loaded with oleoyl-estrone at doses of 12.5 and 50 nmol/g x d using surgically inserted osmotic minipumps. Treatment with oleoyl-estrone resulted in a marked decrease in body weight in both strains, compared with the unchecked growth of controls. In db/db mice, plasma urea and insulin, as well as liver lipid decreased with treatment. In ob/ob mice, the effect on insulin was more marked, in parallel with higher plasma lipids pointing to increased fat mobilisation. The results suggest that oleoyl-estrone effects on body fat reserves and insulin resistance are not mediated by leptin, since ob/ob mice lack this hormone and in the db/db it is present but cannot induce effects because of defective leptin receptors; in both cases oleoyl-estrone treatment lowers body weight.     

Terpenoid biosynthesis in Euphorbia latex

The latex of Euphorbia lathyris can utilize acetate, pyruvate and mevalonate for triterpene synthesis in vitro. Acetyl-CoA, hydroxymethylglutarate, hydroxymethylglutaryl-CoA and isopentenyl pyrophosphate were not effective as precursors for triterpene biosynthesis. Acetate is utilized only by the terpenoid pathway and by the tricarboxylic acid cycle; it is not used for fatty acid synthesis in this system. However, phospholipids were found to be efficient acyl donors for triterpene ester synthesis. The observed selectivity of precursor utilization as well as the observed rates for product formation indicate separate sites for triterpenol and triterpene ester synthesis and that one is not precursor for the other.     

Hepatic glycogen metabolism in the db/db mouse

Summary Knowledge of the metabolic changes that occur in insulin-resistant type 2 diabetes is relatively lacking compared to insulin-deficient type 1 diabetes. This paper summarizes the importance of the C57BL/KsJ-db/db mouse as a model of type 2 diabetes, and illustrates the effects that insulin-deficient and insulin-resistant states have on hepatic glycogen metabolism. A longitudinal study of db/db mice of ages 2–15 weeks revealed that significant changes in certain parameters of hepatic glycogen metabolism occur during this period. The liver glycogen levels were similar between diabetic and control mice. However, glycogen particles from db/db mice were on average smaller in mass and had shorter exterior and interior chain lengths. Total phosphorylase and phosphorylase a activities were elevated in the genetically diabetic mice. This was primarily due to an increase in the amount of enzymic protein apparently the result of a decreased rate of degradation. It was not possible to find a consistent alteration in glycogen synthase activity in the db/db mice. Glycogen synthase and phosphorylase from diabetic liver revealed some changes in kinetic properties in the form of a decrease in V_max, and altered sensitivity to inhibitors like ATP. The altered glycogen structure in db/db mice may have contributed to changes in the activities and properties of glycogen synthase and phosphorylase. The exact role played by hormones (insulin and glucagon) in these changes is not clear but further studies should reveal their contributions. The db/db mouse provides a good model for type 2 diabetes and for fluctuating insulin and glucagon ratios. Its use should clarify the regulation of hepatic glycogen metabolism and other metabolic processes known to be controlled by these hormones. The other animal models of type 2 diabetes, ob/ob mouse and fatty Zucker (fa/fa) rat, show similar impairment of hepatic glycogen metabolism. The concentrations of glycogen metabolizing enzymes are high and in vitro studies indicate enhanced rate of glycogen synthesis and breakdown. However, streptozotocin-induced diabetic animals and BB rats which resemble insulin-deficient type 1 diabetes are characterized by decreased glycogen turnover as a result of reduction in the levels of glycogen metabolizing enzymes.     

Perfused hearts from Type 2 diabetic (db/db) mice show metabolic responsiveness to insulin

Diabetic (db/db) mice provide an animal model of Type 2 diabetes characterized by marked in vivo insulin resistance. The effect of insulin on myocardial metabolism has not been fully elucidated in this diabetic model. In the present study we tested the hypothesis that the metabolic response to insulin in db/db hearts will be diminished due to cardiac insulin resistance. Insulin-induced changes in glucose oxidation (GLUox) and fatty acid (FA) oxidation (FAox) were measured in isolated hearts from control and diabetic mice, perfused with both low as well as high concentration of glucose and FA: 10 mM glucose/0.5 mM palmitate and 28 mM glucose/1.1 mM palmitate. Both in the absence and presence of insulin, diabetic hearts showed decreased rates of GLUox and elevated rates of FAox. However, the insulin-induced increment in GLUox, as well as the insulin-induced decrement in FAox, was similar or even more pronounced in diabetic that in control hearts. During elevated FA and glucose supply, however, the effect of insulin was blunted in db/db hearts with respect to both FAox and GLUox. Finally, insulin-stimulated deoxyglucose uptake was markedly reduced in isolated cardiomyocytes from db/db mice, whereas glucose uptake in isolated perfused db/db hearts was clearly responsive to insulin. These results show that, despite reduced insulin-stimulated glucose uptake in isolated cardiomyocytes, isolated perfused db/db hearts are responsive to metabolic actions of insulin. These results should advocate the use of insulin therapy (glucose-insulin-potassium) in diabetic patients undergoing cardiac surgery or during reperfusion after an ischemic insult.     

Effects of peroxisome proliferators gemfibrozil and clofibrate on syntheses of dolichol and cholesterol in rat liver

The effects of two peroxisome proliferators, gemfibrozil and clofibrate, on syntheses of dolichol and cholesterol in rat liver were investigated. Gemfibrozil did not affect the overall content of dolichyl phosphate, but it changed the chain-length distribution of dolichyl phosphate, increasing the levels of species with shorter isoprene units. Gemfibrozil suppressed synthesis of dolichyl phosphate from [(3)H]mevalonate and [(3)H]farnesyl pyrophosphate in rat liver. In contrast, clofibrate increased the content of dolichol (free and acyl ester forms). It remarkably enhanced dolichol synthesis from mevalonate, but did not affect dolichol synthesis from farnesyl pyrophosphate. Gemfibrozil elevated cholesterol synthesis from [(14)C]acetate, but did not affect the synthesis from mevalonate. Clofibrate suppressed cholesterol synthesis from acetate, but did not affect cholesterol synthesis from mevalonate. These results suggest that gemfibrozil suppresses synthesis of dolichyl phosphate by inhibiting, at the least, the pathway from farnesyl pyrophosphate to dolichyl phosphate. As a result, the chain-length pattern of dolichyl phosphate may show an increase in shorter isoprene units. Clofibrate may increase the content of dolichol by enhancing dolichol synthesis from mevalonate. Gemfibrozil may increase cholesterol synthesis by activating the pathway from acetate to mevalonate. Unlike gemfibrozil, clofibrate may decrease cholesterol synthesis by inhibiting the pathway from acetate to mevalonate.     

Enhanced isoamyl acetate production upon manipulation of the acetyl-CoA node in Escherichia coli

Coenzyme A (CoA) and its thioester derivative acetyl-Coenzyme A (acetyl-CoA) participate in over 100 different reactions in intermediary metabolism of microorganisms. Earlier results indicated that overexpression of upstream rate-limiting enzyme pantothenate kinase with simultaneous supplementation of precursor pantothenic acid to the culture media increased intracellular CoA levels significantly ( approximately 10-fold). The acetyl-CoA levels also increased ( approximately 5-fold) but not as much as that of CoA, showing that the carbon flux from the pyruvate node is rate-limiting upon an increase in CoA levels. In this study, pyruvate dehydrogenase was overexpressed under elevated CoA levels to increase carbon flux from pyruvate to acetyl-CoA. This coexpression did not increase intracellular acetyl-CoA levels but increased the accumulation of extracellular acetate. The production of isoamyl acetate, an industrially useful compound derived from acetyl-CoA, was used as a model reporter system to signify the beneficial effects of this metabolic engineering strategy. In addition, a strain was created in which the acetate production pathway was inactivated to relieve competition at the acetyl-CoA node and to efficiently channel the enhanced carbon flux to the ester production pathway. The synergistic effect of cofactor CoA manipulation and pyruvate dehydrogenase overexpression in the acetate pathway deletion mutant led to a 5-fold increase in isoamyl acetate production. Under normal growth conditions the acetate pathway deletion mutant strains accumulate intracellular pyruvate, leading to excretion of pyruvate. However, upon enhancing the carbon flux from pyruvate to acetyl-CoA, the excretion of pyruvate was significantly reduced.     

Redistribution of metabolic fluxes in the central aerobic metabolic pathway of E. coli mutant strains with deletion of the ackA-pta and poxB pathways for the synthesis of isoamyl acetate

Although the bacterium E. coli is chosen as the host in many bioprocesses, products derived from the central aerobic metabolic pathway often compete with the acetate-producing pathways poxB and ackA-pta for glucose as the substrate. As such, a significant portion of the glucose may be excreted as acetate, wasting substrate that could have otherwise been used for the desired product. The production of the ester isoamyl acetate from acetyl-CoA by ATF2, a yeast alcohol acetyl transferase, was used as a model system to demonstrate the beneficial effects of reducing acetate production. All strains tested for ester production also overexpressed panK, a native E. coli gene that previous studies have shown to increase free intracellular CoA levels when fed with pantothenic acid. A recombinant E. coli strain with a deletion in ackA-pta produces less acetate and more isoamyl acetate than the wild-type E. coli strain. When both acetate-producing pathways were deleted, the acetate production was greatly reduced. However, pyruvate began to accumulate, so that the overall ester production remained largely unchanged. To produce more ester, a previously established strategy of increasing the flux from pyruvate to acetyl-CoA was adopted by overexpressing pyruvate dehydrogenase. The ester production was then 80% higher in the poxB, ackA-pta strain (0.18 mM) than that found in the single ackA-pta mutant (0.10 mM), which also overexpressed PDH.     

The action of nicotinamide on the adenine nucleotide system as well as on mitochondrial oxidation and phosphorylation processes in the liver of db/db strain mice

Both levels of total adenine nucleotides, ATP, AMP, ATP/ADP ratio and phosphate potential of cell and cytosol and the intensity of mitochondrial oxidation (fatty acid beta-oxidation in particular) and phosphorylation are elevated in the liver of db/db mice as compared with control. Presumably these alterations corresponding to the total activation of metabolic processes in db/db mice are mediated by hyperinsulinemia. Nicotinamide treatment (2.5 mg/100 g body weight, 14 days, i.m.) elicits further increase of ATP and total adenine nucleotide levels, cytosolic phosphate potential and activation of mitochondrial oxidation and phosphorylation. The findings obtained can be used for explanation of nicotinamide inhibition of gluconeogenesis, diacylglycerol and phosphoacylglycerol biosynthesis in the liver of db/db mice.     

Two independent biochemical pathways for isopentenyl diphosphate and isoprenoid biosynthesis in higher plants

In the early times of isoprenoid research, a single pathway was found for the formation of the C₅ monomer, isopentenyl diphosphate (IPP), and this acetate/mevalonate pathway was supposed to occur ubiquitously in all living organisms. Now, 40 years later, a totally different IPP biosynthesis route has been detected in eubacteria, green algae and higher plants. In this new pathway glyceraldehyde 3-phosphate (GAP) and pyruvate are precursors of isopentenyl diphosphate, but not acetyl-CoA and mevalonic acid. In green tissues of three higher plants it was shown that all chloroplastbound isoprenoids (β-carotene, phytyl chains of chlorophylls and nona-prenyl chain of plastoquinone-9) are formed via the GAP/pyruvate pathway, whereas the cytoplasmic sterols are formed via the acetate/mevalonate pathway. Also, isoprene, emitted by various plants at high light conditions by action of the plastid-bound isoprene synthase, is formed via the new GAP/pyruvate pathway. Thus, in higher plants, there exist two separate and biochemically different IPP biosynthesis pathways: (1) the novel alternative GAP/pyruvate pathway apparently bound to the plastidic compartment and (2) the classical cytoplasmic acetate/mevalonate pathway. This new GAP/pyruvate pathway for IPP formation allows a reasonable interpretation of previous odd results concerning the biosynthesis of chloroplast isoprenoids, which, so far, had mainly been interpreted assuming compartmentation differences. The novel GAP/pyruvate pathway for IPP formation in plastids appears as a heritage of their prokaryotic, endosymbiotic ancestors.     

Magnetic resonance imaging of progressive cardiomyopathic changes in the db/db mouse

The db/db mouse is a well-established model of diabetes. Previous reports have documented contractile dysfunction (i.e., cardiomyopathy) in these animals, although the extant literature provides limited insights into cardiac structure and function as they change over time. To better elucidate the natural history of cardiomyopathy in db/db mice, we performed cardiac magnetic resonance (CMR) scans on these animals. CMR imaging was conducted with a 4.7-T magnet on female db/db mice and control db/+ littermates at 5, 9, 13, 17, and 22 wk of age. Gated gradient echo sequences were used to obtain cineographic short-axis slices from apex to base. From these images left ventricular (LV) mass (LVM), wall thickness, end-diastolic volume (LVEDV), and ejection fraction (LVEF) were determined. Additionally, cardiac [(18)F]fluorodeoxyglucose ([(18)F]FDG) PET scanning, pressure-volume loops, and real-time quantitative PCR on db/db myocardium were performed. Relative to control, db/db mice developed significant increases in LVM and wall thickness as early as 9 wk of age. LVEDV diverged slightly later, at 13 wk. Interestingly, compared with the baseline level, LVEF in the db/db group did not decrease significantly until 22 wk. Additionally, [(18)F]FDG metabolic imaging showed a 40% decrease in glucose uptake in db/db mice. Furthermore, contractile dysfunction was observed in 15-wk db/db mice undergoing pressure-volume loops. Finally, real-time quantitative PCR revealed an age-dependent recapitulation of the fetal gene program, consistent with a myopathic process. In summary, as assessed by CMR, db/db mice develop characteristic structural and functional changes consistent with cardiomyopathy.     

Lipogenesis in genetically diabetic (db/db) mice: developmental changes in brown adipose tissue, white adipose tissue and the liver

Developmental changes in lipogenesis have been examined in interscapular brown adipose tissue (BAT), epididymal white adipose tissue and the liver of genetically diabetic (db/db) mice and their normal siblings. Lipogenesis was measured in vivo with 3H2O, from weaning (21 days of age) until 20 weeks of age. Hyperinsulinaemia was evident in db/db mice at all ages. Low rates of lipogenesis were observed at weaning in tissues of both groups of mice, but the rate rose rapidly in the first few days post-weaning. In normal mice, peak lipogenesis was obtained in each tissue at 4-5 weeks of age, and there were no major changes (on a whole-tissue basis) thereafter. A different developmental pattern was apparent in db/db mice. The rate of lipogenesis in BAT rose sharply after weaning, reaching a peak at 26 days of age (several times higher than normal mice), and then falling rapidly such that by 45 days of age it was lower than in normal mice; at age 20 weeks lipogenesis in BAT of the diabetic animals was negligible. In white adipose tissue of the db/db mutants lipogenesis (per tissue) reached a maximum at 5 weeks of age, and fell substantially between 10 and 20 weeks of age. Hepatic lipogenesis in the db/db mice rose progressively from weaning until 8 weeks of age, and then decreased. Except at weaning, hepatic lipogenesis (per tissue) was much greater in db/db mice than in normal mice, and the liver was a more important site of lipogenesis in diabetic mice than in normals, accounting for up to 60% of the whole-body total. In contrast, BAT accounted for a considerably smaller proportion of whole-body lipogenesis in db/db mice than in normal mice. It is concluded that there are major developmental differences in lipogenesis between tissues of db/db mice, and between diabetic and normal animals. The data suggest that there is an early and preferential development of insulin resistance in BAT of the db/db mutant.     

Hypertension and disrupted blood pressure circadian rhythm in type 2 diabetic db/db mice

Human Type 2 diabetes is associated with increased incidence of hypertension and disrupted blood pressure (BP) circadian rhythm. Db/db mice have been used extensively as a model of Type 2 diabetes, but their BP is not well characterized. In this study, we used radiotelemetry to define BP and the circadian rhythm in db/db mice. We found that the systolic, diastolic, and mean arterial pressures were each significantly increased by 11, 8, and 9 mmHg in db/db mice compared with controls. In contrast, no difference was observed in pulse pressure or heart rate. Interestingly, both the length of time db/db mice were active (locomotor) and the intensity of locomotor activity were significantly decreased in db/db mice. In contrast to controls, the 12-h light period average BP in db/db mice did not dip significantly from the 12-h dark period. A partial Fourier analysis of the continuous 72-h BP data revealed that the power and the amplitude of the 24-h period length rhythm were significantly decreased in db/db mice compared with the controls. The acrophase was centered at 0141 in control mice, but became scattered from 1805 to 0236 in db/db mice. In addition to BP, the circadian rhythms of heart rate and locomotor activity were also disrupted in db/db mice. The mean arterial pressure during the light period correlates with plasma glucose, insulin, and body weight. Moreover, the oscillations of the clock genes DBP and Bmal1 but not Per1 were significantly dampened in db/db mouse aorta compared with controls. In summary, our data show that db/db mice are hypertensive with a disrupted BP, heart rate, and locomotor circadian rhythm. Such changes are associated with dampened oscillations of clock genes DBP and Bmal1 in vasculature.     

Impaired response of UCP family to cold exposure in diabetic (db/db) mice

Impaired activity of the uncoupling protein (UCP) family has been proposed to promote obesity development. The present study examined differences in UCP responses to cold exposure between leptin-resistance obese (db/db) mice and their lean (C57Ksj) littermates. Basal UCP1 and UCP3 mRNA expression in brown adipose tissue was lower in obese mice compared with lean mice, but UCP2 expression in white adipose tissue (WAT) was higher. Basal skeletal muscle UCP3 did not change remarkably. The UCP family mRNAs, which were upregulated 12 and 24 h after cold exposure (4 degrees C), were returned to prior levels 12 h after rewarming exposure (21 degrees C) in lean mice. The accelerating effects of cold exposure on the UCP family were impaired in db/db obese mice. Together with these changes, WAT lipoprotein lipase mRNA was downregulated, and the concentration of serum free fatty acid was increased in response to cold exposure in the lean mice but not in db/db obese littermates. The impaired function of the UCP family and diminished lipolysis in response to cold exposure indicate that the reduced lipolytic activity may contribute to the inactivation of the UCP family in db/db obese mice.     

Treatment of type 2 diabetic db/db mice with a novel PPARgamma agonist improves cardiac metabolism but not contractile function

Hearts from insulin-resistant type 2 diabetic db/db mice exhibit features of a diabetic cardiomyopathy with altered metabolism of exogenous substrates and reduced contractile performance. Therefore, the effect of chronic oral administration of 2-(2-(4-phenoxy-2-propylphenoxy)ethyl)indole-5-acetic acid (COOH), a novel ligand for peroxisome proliferator-activated receptor-gamma that produces insulin sensitization, to db/db mice (30 mg/kg for 6 wk) on cardiac function was assessed. COOH treatment reduced blood glucose from 27 mM in untreated db/db mice to a normal level of 10 mM. Insulin-stimulated glucose uptake was enhanced in cardiomyocytes from COOH-treated db/db hearts. Working perfused hearts from COOH-treated db/db mice demonstrated metabolic changes with enhanced glucose oxidation and decreased palmitate oxidation. However, COOH treatment did not improve contractile performance assessed with ex vivo perfused hearts and in vivo by echocardiography. The reduced outward K+ currents in diabetic cardiomyocytes were still attenuated after COOH. Metabolic changes in COOH-treated db/db hearts are most likely indirect, secondary to changes in supply of exogenous substrates in vivo and insulin sensitization.     

Anti-hyperlipidemic effect of soybean extract fermented by Bacillus subtilis MORI in db/db mice

The purpose of this study was to investigate the anti-hyperlipidemic effect of soy bean extract solution fermented by Bacillus subtilis MORI (BTD-1E) in obese db/db mice. Eight-week-old male db/db mice were administered 33.3 mg/kg BTD-1E solution orally once a day for four weeks. The BTD-1E group showed significantly lower body weight compared with the db control group (P<0.05). The BTD-1E group showed significantly lower serum total cholesterol and LDL cholesterol levels compared with the db control group, respectively (P<0.05, P<0.01). The BTD-1E group showed significantly decreased liver weight relative to final body weight compared with the db control group (P<0.01). After four weeks of BTD-1E administration, lipid droplets in the liver were apparently decreased in the BTD-1E group compared to the db control group. In summary, our results suggest that BTD-1E has an anti-hyperlipidemic effect in the obese mouse model.     

Rat liver microsomal cholesterol biosynthesis and drug oxidase activity are affected by chromium ions (Cr3+) in vitro

Chromium ions (Cr3+)evoked a biphasic curve of changes of rat liver microsomal cholesterol biosynthesis using [14C]acetate and/or [14C]mevalonate as precursors. While for the lower range of Cr3+ concentrations the rate of cholesterol biosynthesis rises, at concentrations above 8 X 10(-6) M they evoke a decrease in the cholesterol biosynthesis, up to 50% down on its control value at a concentration of 8 X 10(-4) M. Differences were more pronounced when using [14C]mevalonate instead of [14C]acetate as precursor. The activity of the microsomal enzyme biphenyl-4-hydroxylase showed an equally intense rise to that of cholesterol biosynthesis up to a 8 X 10(-6) M Cr3+ concentration. Above this concentration, however, the activity of the enzyme starts to drop. NADPH-cytochrome c reductase and NADPH-oxidase were decreased at all Cr3+ concentrations used, which cover a 100-fold range. Lineweaver-Burk plots of the cytoplasmic glucose-6-phosphate dehydrogenase demonstrated an uncompetitive mechanism of inhibition by Cr3+ ions. The results are discussed in terms of the possible significance of the Cr3+ concentration-dependent effects on cholesterol biosynthesis, with the observed atherosclerosis in Cr-deficient humans.     

Hyperleptinemia and reduced TNF-alpha secretion cause resistance of db/db mice to endotoxin

Leptin deficiency in ob/ob mice increases susceptibility to endotoxic shock, whereas leptin pretreatment protects them against LPS-induced lethality. Lack of the long-form leptin receptor (Ob-Rb) in db/db mice causes resistance. We tested the effects of LPS in C57BL/6J db(3J)/db(3J) (BL/3J) mice, which express only the circulating leptin receptors, compared with C57BL/6J db/db (BL/6J) mice, which express all short-form and circulating isoforms of the leptin receptor. Intraperitoneal injections of LPS significantly decreased rectal temperature and increased leptin, corticosterone, and free TNF-alpha in fed and fasted BL/3J and BL/6J mice. TNF-alpha was increased three- and fourfold in BL/3J and BL/6J, respectively. LPS (100 microg) caused 50% mortality of fasted BL/6J mice but caused no mortality in fasted BL/3J mice. Pretreatment of fasted BL/3J mice with 30 microg leptin prevented the drop in rectal temperature, blunted the increase in corticosterone, but had no effect on TNF-alpha induced by 100 microg LPS. Taken together, these data provide evidence that fasted BL/3J mice are more resistant than BL/6J mice to LPS toxicity, presumably due to the absence of leptin receptors in BL/3J mice. This resistance may be due to high levels of free leptin cross-reacting with other cytokine receptors.