Effects of glucagon and insulin on lipolysis and ketogenesis in sheep.
The hepatic and portal productions of acetoacetate and beta-hydroxybutyrate and lipolysis were studied in normal and insulin-controlled alloxan-diabetic sheep. Since hyperinsulinemia is associated with glucagon administration, the latter group of sheep were used to maintain constant plasma insulin levels. After control values were obtained glucagon was infused intraportally at 90 mug/hr for two hours. The ketone body production by portal drained viscera was not significantly affected by glucagon. In alloxanized sheep, glucagon significantly (P less than 0.01) increased net hepatic production of acetoacetate (from -0.54 +/- 0.08 to 0.46 +/- 0.07 g/hr). Lipolysis also increased. However, in the normal sheep, hyperinsulinemia prevented any stimulatory effect of glucagon on hepatic ketogenesis and lipolysis. Therefore, while glucagon appears capable of stimulating ketogenesis andlipolysis, these effects are readily suppressed by insulin. (+info)
Structural and functional changes in acute liver injury.
Carbon tetrachloride produces liver cell injury in a variety of animal species. The first structurally recognizable changes occur in the endoplasmic reticulum, with alteration in ribosome-membrane interactions. Later there is an increase in intracellular fat, and the formation of tangled nets of the ergastoplasm. At no time are there changes in mitochondria or single membrane limited bodies in cells with intact plasmalemma, although a relative increase in cell sap may appear. In dead cells (those with plasmalemma discontinuties) crystalline deposits of calcium phosphatase may be noted. Functional changes are related to the endoplasmic reticulum and the plasma membrane. An early decrease in protein synthesis takes place; an accumulation of neutral lipid is related to this change. Later alterations in the ergastoplasmic functions (e.g., mixed function oxidation) occurs. Carbon tetrachloride is not the active agent; rather, a product of its metabolism, probably the CC1, free radical, is. The mechanisms of injury include macromolecular adduction and peroxide propagation. A third possibility includes a cascade effect with the production of secondary and tertiary products, also toxic in nature, with the ability to produce more widespread damage to intracellular structures. (+info)
Quantitative aspects in the assessment of liver injury.
Liver function data are usually difficult to use in their original form when one wishes to compare the hepatotoxic properties of several chemical substances. However, procedures are available for the conversion of liver function data into quantal responses. These permit the elaboration of dose-response lines for the substances in question, the calculation of median effective doses and the statistical analysis of differences in liver-damaging potency. These same procedures can be utilized for estimating the relative hazard involved if one compares the liver-damaging potency to the median effective dose for some other pharmacologie parameter. Alterations in hepatic triglycerides, lipid peroxidation, and the activities of various hepatic enzymes can also be quantitiated in a dose-related manner. This permits the selection of equitoxic doses required for certain comparative studies and the selection of doses in chemical interaction studies. The quantitative problems involved in low-frequency adverse reactions and the difficulty these present in the detection of liver injury in laboratory animals are discussed. (+info)
Blocking very late antigen-4 integrin decreases leukocyte entry and fatty streak formation in mice fed an atherogenic diet.
Atherosclerotic lesion development is characterized by the recruitment of leukocytes, principally monocytes, to the vessel wall. Considerable interest has been focused on the adhesion molecule(s) involved in leukocyte/endothelial interactions. The goal of the present study was to determine the role of the very late antigen-4 (VLA-4) integrin/ligand interaction in fatty streak development using murine models. Because alpha4 null mice are not viable, a peptidomimetic was used to block VLA-4-mediated leukocyte binding. The ability of a synthetic peptidomimetic of connecting segment-1 (CS-1 peptide) to block the recruitment of leukocytes and the accumulation of lipid in the aortic sinus of either wild-type mice (strain C57BL/6J) or mice with a low-density lipoprotein null mutation (LDLR-/-) maintained on an atherogenic diet was assessed. The active (Ac) CS-1 peptide or scrambled (Sc) CS-1 peptide was delivered subcutaneously into mice using a mini osmotic pump. Mice were exposed to the peptide for 24 to 36 hours before the onset of the atherogenic diet. In C57BL/6J mice, leukocyte entry into the aortic sinus, as assessed by en face preparations, was inhibited by the active peptide (Ac=28+/-4, Sc=54+/-6 monocytes/valve; P=0.004). Additionally, frozen sections stained with Oil Red O were analyzed to assess lipid accumulation in the aortic sinus. C57BL/6J mice that received the (Ac) compound demonstrated significantly reduced lesion areas as compared with mice that received the (Sc) peptide (Ac=4887+/-4438 microm2, Sc=15 009 +/-5619 microm2; P<0.0001). In a separate study, LDLR-/- mice were implanted with pumps containing either the (Ac) or (Sc) peptide before initiation of the atherogenic diet. Because LDLR-/- mice fed a chow diet displayed small lesions at 14 weeks, the effects of the peptide seen in these animals represented a change in early lipid accumulation rather than initiation. By using whole-mount preparations, the (Ac) but not the (Sc) peptide significantly reduced the area of lipid accumulation in the aortic sinus, resulting in an approximate 66% decrease. Plasma analysis from all studies revealed concentrations of peptide to be present at levels previously determined by in vitro analysis to block adhesion. (Ac) CS-1 peptide, which blocks VLA-4 on the leukocyte surface, is effective in reducing leukocyte recruitment and lipid accumulation in the aortic sinus. The present study provides in vivo evidence that the VLA-4 integrin plays an important role in the initiation of the atherosclerotic lesion and lipid accumulation, and it suggests a potential therapeutic strategy for this disease. (+info)
Cardiomegaly in the juvenile visceral steatosis (JVS) mouse is reduced with acute elevation of heart short-chain acyl-carnitine level after L-carnitine injection.
The long-term administration of L-carnitine was very effective in preventing cardiomegaly in juvenile visceral steatosis (JVS) mice, which was confirmed by heart weight as well as the lipid contents in heart tissue. After i.p. injection of L-carnitine, the concentration of free carnitine in heart remained constant, although serum free carnitine level increased up to 80-fold. On the other hand, a significant increase in short-chain acyl-carnitine level in heart was observed. These results suggest that increased levels of short-chain acyl-carnitine, not free carnitine, might be a key compound in the protective effect of L-carnitine administration in JVS mice. (+info)
Further studies on the mechanism of adrenaline-induced lipolysis in lipid micelles.
Lipase [EC 188.8.131.52] depleted lipid micelles, in which lipolysis was not elicited by adrenaline, were prepared from lipid micelles. When these lipase-depleted lipid micelles incubated with adipose tissue extract containing lipase activity, adrenaline-induced lipolysis was restored to almost the same level as that of native lipid micelles. Adrenaline-induced lipolysis was not restored when the lipase-depleted lipid micelles were homogenized or sonicated. Various tissue extracts from kidney, lung, liver, and pancreas, and post-heparin plasma, which contained lipase activity, restored adrenaline-induced lipolysis in lipase-depleted lipid micelles. (+info)
Suppression of atherosclerotic development in Watanabe heritable hyperlipidemic rabbits treated with an oral antiallergic drug, tranilast.
BACKGROUND: Inflammatory and immunological responses of vascular cells have been shown to play a significant role in the progression of atheromatous formation. Tranilast [N-(3,4-dimethoxycinnamoyl) anthranillic acid] inhibits release of cytokines and chemical mediators from various cells, including macrophages, leading to suppression of inflammatory and immunological responses. This study tested whether tranilast may suppress atheromatous formation in Watanabe heritable hyperlipidemic (WHHL) rabbits. METHODS AND RESULTS: WHHL rabbits (2 months old) were given either 300 mg x kg-1 x d-1 of tranilast (Tranilast, n=12) or vehicle (Control, n=13) PO for 6 months. Tranilast treatment was found to suppress the aortic area covered with plaque. Immunohistochemical analysis showed that there was no difference in the percentage of the RAM11-positive macrophage area and the frequency of CD5-positive cells (T cells) in intimal plaques between Tranilast and Control. Major histocompatibility complex (MHC) class II expression in macrophages and interleukin-2 (IL-2) receptor expression in T cells, as markers of the immunological activation in these cells, was suppressed in atheromatous plaque by tranilast treatment. Flow cytometry analysis of isolated human and rabbit peripheral blood mononuclear cells showed that an increase in expression both of MHC class II antigen on monocytes by incubation with interferon-gamma and of IL-2 receptor on T cells by IL-2 was suppressed by the combined incubation with tranilast. CONCLUSIONS: The results indicate that tranilast suppresses atherosclerotic development partly through direct inhibition of immunological activation of monocytes/macrophages and T cells in the atheromatous plaque. (+info)
Genetic evidence for ATP-dependent endoplasmic reticulum-to-Golgi apparatus trafficking of ceramide for sphingomyelin synthesis in Chinese hamster ovary cells.
LY-A strain is a Chinese hamster ovary cell mutant resistant to sphingomyelin (SM)-directed cytolysin and has a defect in de novo SM synthesis. Metabolic labeling experiments with radioactive serine, sphingosine, and choline showed that LY-A cells were defective in synthesis of SM from these precursors, but not syntheses of ceramide (Cer), glycosphingolipids, or phosphatidylcholine, indicating a specific defect in the conversion of Cer to SM in LY-A cells. In vitro experiments showed that the specific defect of SM formation in LY-A cells was not due to alterations in enzymatic activities responsible for SM synthesis or degradation. When cells were treated with brefeldin A, which causes fusion of the Golgi apparatus with the endoplasmic reticulum (ER), de novo SM synthesis in LY-A cells was restored to the wild-type level. Pulse-chase experiments with a fluorescent Cer analogue, N-(4,4-difluoro-5,7-dimethyl-4-bora-3a, 4a-diaza-s-indacene-3-pentanoyl)-D-erythro-sphingosine (C5-DMB-Cer), revealed that in wild-type cells C5-DMB-Cer was redistributed from intracellular membranes to the Golgi apparatus in an intracellular ATP-dependent manner, and that LY-A cells were defective in the energy-dependent redistribution of C5-DMB-Cer. Under ATP-depleted conditions, conversion of C5-DMB-Cer to C5-DMB-SM and of [3H]sphingosine to [3H]SM in wild-type cells decreased to the levels in LY-A cells, which were not affected by ATP depletion. ER-to-Golgi apparatus trafficking of glycosylphosphatidylinositol-anchored or membrane-spanning proteins in LY-A cells appeared to be normal. These results indicate that the predominant pathway of ER-to-Golgi apparatus trafficking of Cer for de novo SM synthesis is ATP dependent and that this pathway is almost completely impaired in LY-A cells. In addition, the specific defect of SM synthesis in LY-A cells suggests different pathways of Cer transport for glycosphingolipids versus SM synthesis. (+info)