A simple synthesis of 8-(methoxycarbonyl)octyl 3,6-di-O-(alpha-D-mannopyranosyl)-alpha-D-mannopyranoside and derivatives and their use in the preparation of neoglycoconjugates.

8-(Methoxycarbonyl)octyl 3,6-di-O-(alpha-D-mannopyranosyl)-alpha-D-mannopyranoside (10) was synthesized in 54% yield by regioselective diglycosylation of unprotected mannoside 4, employing the trichloroacetimidate donor 1, followed by debenzoylation. Derivatives of compounds 4 and 10 were used to prepare conjugates containing fluorochromes for the study of carbohydrate-lectin interactions, as well as conjugates with phospholipids for the preparation of liposomes.     

Prostaglandin synthesis in isolated glomeruli.

Prostaglandins are thought to play an important role in the local regulation of glomerular blood flow and in the release of renin from the juxtaglomerular apparatus. We therefore examined prostaglandin synthesis by isolated rat glomeruli. Isolated glomeruli were either prelabeled with [14C] arachidonic acid or were incubated with [14C] arachidonic acid for the entire experimental incubation in Krebs buffer. Prostaglandin synthesis was determined by thin layer radio-chromatography of acid extracts of the supernatant solutions. Indomethacin inhibitable synthesis of small amounts of 6-keto-PGF1 alpha, the metabolite of prostacyclin (PGI2,) and larger amounts of PGF2 alpha, and PGE2, and possibly thromboxane B2 (TXB2) by isolated glomeruli could be demonstrated with either prelabeling or direct incubation. These findings support the hypothesis that prostaglandins are produced within the glomerulus where they may affect local glomerular blood flow and function.     

Control of canine kidney cortex slice volume and ion distribution at hypothermia by impermeable anions

Hypothermia induces swelling of dog kidney cortex slices. Swelling of cells during hypothermia is related to a number of factors including the permeability of Cl⁻. By substituting lactobionate for Cl⁻, while maintaining isoosmotic conditions, swelling is prevented. Lactobionate is an impermeable anion and its presence in the suspending fluid prevents swelling of dog kidney cortex slices in salts of Na⁺, K⁺ or combinations of Na⁺ and K⁺ even in the presence of metabolic inhibitors. By maintaining a ratio of 80 mM lactobionate: 60 mM chloride and an appropriate ratio of Na⁺:K⁺ (80 mM:60 mM), both the total tissue H₂O and ratio of intracellular K⁺/Na⁺ are kept within normal ranges during hypothermic incubation of tissue slices. Kidney cortex slices suspended in this medium at 30 °C respire at a rate 30–40% slower than that of control slices suspended in saline. A similar result is obtained by adding ouabain to slices suspended in saline. This suggests that the Na⁺-pump activity is suppressed under these conditions and results in a reduced energy demand on the cell. These results are discussed in relation to utilizing this type of solution for long-term perfusion preservation of kidneys for transplantation.     

Declining viability and lipid degradation during pollen storage

Declining viability of pollen during storage at 24° C in atmospheres of 40% relative humidity (RH) and 75% RH was studied, with special emphasis on lipid changes. Pollens of Papaver rhoeas and Narcissus poeticus, characterized by a high linolenic acid content, were compared with Typha latifolia pollen which has a low linolenic acid content. The rationale behind this was to answer the question of whether lipid peroxidation is involved in the rapid viability loss and reduced membrane integrity of, in particular, the unsaturated-lipid pollen types. Viability and membrane integrity degraded more rapidly at 75% RH than at 40% RH. All pollen species showed deesterification of acyl chains of lipids but no detectable peroxidation at both RH levels. Considerable amounts of lipid-soluble antioxidants were detected that did not degrade during storage. Free fatty acids and lysophospholipids were formed during storage, the effects of which on membranes are discussed. These degradation products were very prominent in the short-lived Papaver pollen. The loss of viability does coincide with phospholipid deesterification. A significant decrease of the phospholipid content occurred at 75% RH, but not at 40% RH. Based on compositional analyses of phospholipids and newly formed free fatty acids, it was concluded that the deesterification of acyl chains from the lipids occurred at random. We suggest that, due to the low water content of the pollen, free radicals rather than unspecific acyl hydrolases are involved in the deesterification process.     

Abrupt rather than gradual hormonal changes induce postpartum blues-like behavior in rats

AimsPostpartum blues is thought to be related to hormonal events accompanying delivery. We investigated whether blues-like symptoms depend on the rate of the decline of hormones, by comparing the behavioral consequences of an abrupt versus a gradual decline of gonadal hormones in an animal model.MethodsFemale rats were treated with estrogen and progesterone for 23 days, administered either by injections or by subcutaneously implanted tubes filled with hormones. A gradual hormone decline was achieved by discontinuation of the injections; and rapid decline by removal of the tubes. Control groups received either a continued treatment or no hormones. In the period following the decline the stress-reactivity was tested with an acoustic startle test on 3 consecutive days, and anxiety behavior with an open-field test on the 2nd day. The Hypothalamus-, Pituitary-, Adrenal-axis (HPA-axis) response to stress was measured by assessing the corticosterone levels and hypothalamic c-fos expression stress-response at the 4th day.Key findingsThe rapid decline of hormones induced an increased startle response lasting for two days, and increased anxiety-like behavior in the open field. This was not found in the gradual-decline and control groups. The HPA-axis response to stress was decreased in all hormone-treated animals.SignificanceThis animal study suggests that: 1) abrupt rather than gradual hormonal changes induce increased stress-reactivity and anxiety-like behavior; 2) postpartum blues may result from differences in the capacity to adapt to the changes of gonadal hormones; 3) Recovery of pregnancy-induced diminished HPA-axis response is independent of the postpartum hormone kinetics.     

Differential effects of pharmacological liver X receptor activation on hepatic and peripheral insulin sensitivity in lean and ob/ob mice

Liver X receptor (LXR) agonists have been proposed to act as anti-diabetic drugs. However, pharmacological LXR activation leads to severe hepatic steatosis, a condition usually associated with insulin resistance and type 2 diabetes mellitus. To address this apparent contradiction, lean and ob/ob mice were treated with the LXR agonist GW-3965 for 10 days. Insulin sensitivity was assessed by hyperinsulinemic-euglycemic clamp studies. Hepatic glucose production (HGP) and metabolic clearance rate (MCR) of glucose were determined with stable isotope techniques. Blood glucose and hepatic and whole body insulin sensitivity remained unaffected upon treatment in lean mice, despite increased hepatic triglyceride contents (61.7 +/- 7.2 vs. 12.1 +/- 2.0 nmol/mg liver, P < 0.05). In ob/ob mice, LXR activation resulted in lower blood glucose levels and significantly improved whole body insulin sensitivity. GW-3965 treatment did not affect HGP under normo- and hyperinsulinemic conditions, despite increased hepatic triglyceride contents (221 +/- 13 vs. 176 +/- 19 nmol/mg liver, P < 0.05). Clamped MCR increased upon GW-3965 treatment (18.2 +/- 1.0 vs. 14.3 +/- 1.4 ml x kg(-1) x min(-1), P = 0.05). LXR activation increased white adipose tissue mRNA levels of Glut4, Acc1 and Fasin ob/ob mice only. In conclusion, LXR-induced blood glucose lowering in ob/ob mice was attributable to increased peripheral glucose uptake and metabolism, physiologically reflected in a slightly improved insulin sensitivity. Remarkably, steatosis associated with LXR activation did not affect hepatic insulin sensitivity.     

The farnesoid X receptor modulates hepatic carbohydrate metabolism during the fasting-refeeding transition

The liver plays a central role in the control of blood glucose homeostasis by maintaining a balance between glucose production and utilization. The farnesoid X receptor (FXR) is a bile acid-activated nuclear receptor. Hepatic FXR expression is regulated by glucose and insulin. Here we identify a role for FXR in the control of hepatic carbohydrate metabolism. When submitted to a controlled fasting-refeeding schedule, FXR(-/-) mice displayed an accelerated response to high carbohydrate refeeding with an accelerated induction of glycolytic and lipogenic genes and a more pronounced repression of gluconeogenic genes. Plasma insulin and glucose levels were lower in FXR(-/-) mice upon refeeding the high-carbohydrate diet. These alterations were paralleled by decreased hepatic glycogen content. Hepatic insulin sensitivity was unchanged in FXR(-/-) mice. Treatment of isolated primary hepatocytes with a synthetic FXR agonist attenuated glucose-induced mRNA expression as well as promoter activity of L-type pyruvate kinase, acetyl-CoA carboxylase 1, and Spot14. Moreover, activated FXR interfered negatively with the carbohydrate response elements regions. These results identify a novel role for FXR as a modulator of hepatic carbohydrate metabolism.     

Acute inhibition of hepatic beta-oxidation in APOE*3Leiden mice does not affect hepatic VLDL secretion or insulin sensitivity

Hepatic VLDL and glucose production is enhanced in type 2 diabetes and associated with hepatic steatosis. Whether the derangements in hepatic metabolism are attributable to steatosis or to the increased availability of FA metabolites is not known. We used methyl palmoxirate (MP), an inhibitor of carnitine palmitoyl transferase I, to acutely inhibit hepatic FA oxidation and investigated whether the FAs were rerouted into VLDL secretion and whether this would affect hepatic glucose production. After an overnight fast, male APOE3*Leiden transgenic mice received an oral dose of 10 mg/kg MP. Administration of MP led to an 83% reduction in plasma beta-hydroxybutyrate (ketone body) levels compared with vehicle-treated mice (0.47 +/- 0.07 vs. 2.81 +/- 0.16 mmol/l, respectively; P < 0.01), indicative of impaired ketogenesis. Plasma FFA levels were increased by 32% and cholesterol and insulin levels were decreased by 17% and 50%, respectively, in MP-treated mice compared with controls. MP treatment led to a 30% increase in liver triglyceride (TG) content. Surprisingly, no effect on hepatic VLDL-TG production was observed between the groups at 8 h after MP administration. In addition, the capacity of insulin to suppress endogenous glucose production was unaffected in MP-treated mice compared with controls. In conclusion, acute inhibition of FA oxidation increases hepatic lipid content but does not stimulate hepatic VLDL secretion or reduce insulin sensitivity.     

The role of transhepatic bile salt flux in the control of hepatic secretion of triacylglycerol-rich lipoproteins in vivo in rodents

Bile salts (BS) have been shown to suppress the secretion of very-low-density lipoprotein-triglyceride (VLDL-TG) in rat and human hepatocytes in vitro. In the present study, we investigated whether the transhepatic BS flux affects VLDL-TG concentration and hepatic VLDL-TG secretion in vivo. In rats, the transhepatic BS flux was quantitatively manipulated by 1-week chronic bile diversion (BD), followed by intraduodenal infusion with taurocholate (TC) or saline for 6 h. In mice, the transhepatic BS flux was manipulated by a 3-week dietary supplementation with TC (0.5 wt.%) or cholestyramine (2 wt.%). In rats, BD followed by saline or TC infusion did not affect plasma triacylglycerol (TG) concentration, hepatic TG production rate or VLDL lipid composition, compared to control rats. In mice supplemented for 3 weeks with TC or cholestyramine, the transhepatic BS flux was increased by 335% and decreased by 48%, respectively, compared to controls. Among the three experimental groups of mice, an inverse relationship between transhepatic BS flux and either plasma TG concentration (R(2)=0.89) or VLDL-TG production rate (R(2)=0.87) was observed, but differences were relatively small. Present data support the concept that BS can reduce VLDL-TG concentration and inhibit hepatic TG secretion in vivo; however, this occurs only at supraphysiological transhepatic BS fluxes in mice.