Nitric oxide hemoglobin in mice and rats in endotoxic shock.

Mice given ip bacterial endotoxin (LPS) at 10 mg/kg showed a statistically significant decrease in plasma glucose and an increase in hematocrit at 2 h after injection. Glucose was still decreased at 4 h, but the hematocrit had returned to control values. Nitrosylated hemoglobin (HbNO) was detected at 3, but not at 2 h. By 4 h it had increased 5-fold. When N-monomethylarginine (NMMA) at 100 mg/kg, ip was given 2 h after LPS in mice, the HbNO concentration at 4 h was significantly reduced, but the hypoglycemia was worsened because NMMA itself produced a significant hypoglycemia. Rats given iv LPS, 20 mg/kg, showed a fleeting, transient rise in mean arterial pressure (MAP) lasting only a few min. Thereafter, the MAP tended to drift slowly downward over 4 h, but when the MAP at 30 min intervals was compared to the pre-LPS MAP, there were no significant differences. Plasma glucose in unanesthetized rats was significantly elevated at 1 h, back to control at 2 h, and significantly decreased at 3 h. HbNO was detected as early as 1 h after injection. By 2 h the HbNO concentrations exceeded the highest levels found in mice, and they were still increasing as late as 5 h after injection. Unanesthetized rats showed toxic signs and 3/12 rats died within 4 hours of LPS administration. These results are consistent with a model for endotoxic shock in which LPS stimulates an inducible pathway for NO synthesis.     

Hepatic response to the oxidative stress induced by E. coli endotoxin: Glutathione as an index of the acute phase during the endotoxic shock

Reactive oxygen species are important mediators of cellular damage during endotoxic shock. In order to investigate the hepatic response to the oxidative stress induced by endotoxin, hepatic and plasma glutathione (total, GSH and GSSG), GSSG/GSH ratio as well as Mn-superoxide dismutase and catalase activities were determined during the acute and recovery phases of reversible endotoxic shock in the rat. A significant increase in liver and plasma total glutathione content was observed 5 h after endotoxin treatment (acute phase), followed by a diminution of these parameters below control values at 48 h (recovery phase). The significant increases of GSSG levels and GSSG/GSH ratio are indicative of oxidative stress occurring during the acute phase. Liver Mn-SOD activity showed a similar time dependency as the GSSG/GSH ratio; however, a marked decrease in the liver catalase activity was observed during the process. These results indicate the participation of liver glutathione in the response to endotoxin and the possible use of plasma glutathione levels and GSSG/GSH ratio as indicators of the acute phase during the endotoxic process. (Mol Cell Biochem 159: 115-121, 1996)     

Time course of the hepatic adaptation to TPN: interaction with glycogen depletion

In response to chronic (5 days) TPN, the liver becomes a major site of glucose disposal, removing approximately 45% (4.5 mg.kg(-1).min(-1)) of exogenous glucose. Moreover, approximately 70% of glucose is not stored but released as lactate. We aimed to determine in chronically catheterized conscious dogs the time course of adaptation to TPN and the glycogen depletion impact on early time course. After an 18-h (n = 5) fast, TPN was infused into the inferior vena cava for 8 (n = 5) or 24 h (n = 6). A third group, of 42-h-fasted animals (n = 6), was infused with TPN for 8 h. TPN was infused at a rate designed to match the dog's calculated basal energy and nitrogen requirements. NHGU (-2.3 +/- 0.1 to 2.2 +/- 0.7 to 3.9 +/- 0.6 vs. -1.7 +/- 0.3 to 1.1 +/- 0.5 to 2.9 +/- 0.4 mg.kg(-1).min(-1), basal to 4 to 8 h, 18 vs. 42 h) and net hepatic lactate release (0.7 +/- 0.3 to 0.6 +/- 0.1 to 1.4 +/- 0.2 vs. -0.6 +/- 0.1 to 0.1 +/- 0.1 to 0.8 +/- 0.1 mg.kg(-1).min(-1), basal to 4 to 8 h) increased progressively. Net hepatic glycogen repletion and tracer determined that glycogen syntheses were similar. After 24 h of TPN, NHGU (5.4 +/- 0.6 mg.kg(-1).min(-1)) and net hepatic lactate release (2.6 +/- 0.4 mg.kg(-1).min(-1)) increased further. In summary, 1) most hepatic adaptation to TPN occurs within 24 h after initiation of TPN, and 2) prior glycogen depletion does not augment hepatic adaptation rate.     

TRPV1-mediated protection against endotoxin-induced hypotension and mortality in rats

This study was designed to test the hypothesis that the transient receptor potential vanilloid type 1 (TRPV1) channel, expressed primarily in sensory nerves, and substance P (SP), released by sensory nerves, play a protective role against lipopolysaccharide (LPS)-induced hypotension. LPS (10 mg/kg iv) elicited tachycardia and hypotension in anesthetized male Wistar rats, which peaked at 10 min and gradually recovered 1 h after the injection. Blockade of TRPV1 with its selective antagonist capsazepine (CAPZ, 3 mg/kg iv) impaired recovery given that the fall in mean arterial pressure (MAP) was greater 1 h after CAPZ plus LPS injections compared with LPS injection alone (45 +/- 5 vs. 25 +/- 4 mmHg, P < 0.05). Blockade of the neurokinin 1 (NK1) receptor with its selective antagonists RP-67580 (5 mg/kg iv) or L-733,060 (4 mg/kg iv) prevented recovery, considering that falls in MAP were not different 1 h after injections of NK1 antagonists plus LPS from their peak decreases (66 +/- 9 vs. 74 +/- 5 mmHg or 60 +/- 7 vs. 69 +/- 3 mmHg, respectively, P > 0.05). LPS increased plasma SP, norepinephrine (NE), and epinephrine (Epi) levels compared with vehicles, and the increases in plasma SP, NE, and Epi were significantly inhibited by CAPZ or RP-67580. The survival rate at 24 or 48 h after LPS injection (20 mg/kg ip) was lower in conscious rats pretreated with CAPZ or RP-67580 compared with rats treated with LPS alone (P < 0.05). Thus our results show that the TRPV1, possibly via triggering release of SP which activates the NK1 and stimulates the sympathetic axis, plays a protective role against endotoxin-induced hypotension and mortality, suggesting that TRPV1 receptors are essential in protecting vital organ perfusion and survival during the endotoxic condition.     

Route-dependent effect of nutritional support on liver glucose uptake

The liver is a major site of glucose disposal during chronic (5 day) total parenteral (TPN) and enteral (TEN) nutrition. Net hepatic glucose uptake (NHGU) is dependent on the route of delivery when only glucose is delivered acutely; however, the hepatic response to chronic TPN and TEN is very similar. We aimed to determine whether the route of nutrient delivery altered the acute (first 8 h) response of the liver and whether chronic enteral delivery of glucose alone could augment the adaptive response to TPN. Chronically catheterized conscious dogs received either TPN or TEN containing glucose, Intralipid, and Travasol for either 8 h or 5 days. Another group received TPN for 5 days, but approximately 50% of the glucose in the nutrition was given via the enteral route (TPN+EG). Hepatic metabolism was assessed with tracer and arteriovenous difference techniques. In the presence of similar arterial plasma glucose levels (approximately 6 mM), NHGU and net hepatic lactate release increased approximately twofold between 8 h and 5 days in TPN and TEN. NHGU (26 +/- 1 vs. 23 +/- 3 micromol.kg(-1).min(-1)) and net hepatic lactate release (44 +/- 1 vs. 34 +/- 6 micromol.kg(-1).min(-1)) in TPN+EG were similar to results for TPN, despite lower insulin levels (96 +/- 6 vs. 58 +/- 16 pM, TPN vs. TPN+EG). TEN does not acutely enhance NHGU or disposition above that seen with TPN. However, partial delivery of enteral glucose is effective in decreasing the insulin requirement during chronic TPN.     

Effect of cortisol on hepatic gluconeogenesis in the fetal sheep

To determine whether the prenatal surge in cortisol induces the onset of gluconeogenesis in the fetal sheep, we performed studies in eight fetal sheep of 124 +/- 3 days gestational age. Catheters were inserted chronically in the descending aorta, inferior vena cava, and hepatic and umbilical veins, allowing the measurement of substrate flux across the liver and placenta. Cortisol was infused over a 48-h period, raising plasma cortisol concentrations from 3.5 +/- 2.5 ng/ml to 78 +/- 22 ng/ml at 24 h and 111 41 ng/ml at 48 h. At 24 and 48 h, [14C]lactate was infused into the inferior vena cava, and blood samples were obtained to measure plasma concentrations and specific activities of glucose and lactate. Comparison of the cortisol-treated group with an untreated control group of animals revealed no differences in blood gases, haemoglobin concentrations, or glucose and lactate levels. Similarly, there were no differences between groups in liver oxygen consumption, glucose and lactate flux, or gluconeogenesis from lactate. In two animals we demonstrated hepatic glucose production from lactate. One of these was in active labor at the time of study, and one aborted within hours of the study. We conclude that the prenatal cortisol surge alone is not responsible for the onset of hepatic gluconeogenesis in the perinatal period. However, cortisol may have a permissive action, promoting hepatic gluconeogenesis in response to other hormonal stimuli.     

Evaluation of thyrotropin releasing hormone as a therapeutic intervention for endotoxemia

Thyrotropin releasing hormone (TRH) has been reported to reduce endotoxin-induced hypotension and mortality rate in conscious rats. Limited data are available to explain these effects. We evaluated hemodynamic parameters, metabolic function, tissue injury, and survival rate in three groups of instrumented conscious rats following intravenous endotoxin (20 mg/kg, LD/90-24 h) challenge. Pretreatment with TRH (2.0 mg/kg, i.v.) was administered 10 min before endotoxin (n = 10) and control (n = 10) animals were given an equivalent volume of saline. The post-treated group (n = 7) was given TRH at the nadir of the hypotensive response following endotoxin to duplicate published protocols. 5 min after endotoxin blood pressure and cardiac output were significantly higher in the post and pre-treatment groups, respectively, compared to the untreated group. There were no differences at other times. Systemic vascular resistance was not affected by either treatment mode at any time. TRH treatment following endotoxin resulted in transient increases in heart and respiration rates and decreased central venous pressure during the first 30 min. Metabolic function indicated by measurements of glucose, lactate, hematocrit, pH, PO2, and PCO2 at 60 and 240 min after endotoxin was not modified by TRH. The hemorrhagic small intestine characteristic of this model was not improved by either treatment mode. Mortality rates at 4 h after endotoxin were 20% for the untreated, 40% for the pre-treated, and 43% for the post-treated. These results suggest TRH exerts early transient effects on cardiovascular responses evoked by endotoxin in the conscious rat but no lasting beneficial effects were found to support the use of TRH as a mono-therapy for endotoxemia.     

Blood pressure and other physiological responses in awake and anesthetized guinea pigs

The effect of combinations of injectable anesthetics on mean arterial blood pressure, blood gases, heart rate and respiration of the guinea pig (NIH Outbred strain) was investigated. After a 30 minute period in which baseline resting cardiorespiratory measurements were obtained, five groups of six pigmented animals having indwelling carotid cannulas were anesthetized with (a) ketamine hydrochloride (30 mg/kg, im)/xylazine (5 mg/kg, im); (b) sodium pentobarbital (15 mg/kg, ip)/fentanyl-droperidol (0.4 mg/kg, im); (c) diazepam (5mg/kg, ip)/fentanyl citrate (0.32 mg/kg, im); (d) diazepam (5 mg/kg, ip)/alphaxalone-alphadolone acetate (45 mg/kg, im); or (e) 1% alpha-chloralose-40% urethane (0.8 ml/100g, ip). Animals were not respirated artificially and no supplemental doses of anesthetic were given. Resting blood pressure in awake animals was measured over time for as long as cannulas remained patent (109 measurements). Mean resting blood pressure, for this strain of guinea pigs, was determined to be 53.1 +/- 4.2 mmHg. There was no indication that mean arterial blood pressure changed with age in animals varying in weight from 215 g to 550 g. Under diazepam/fentanyl, blood pressure rose significantly above resting level to a mean of 71.1 +/- 6.1 mmHg. With the other four combinations, blood pressure stabilized near, but below pre-anesthesia levels (ketamine/xylazine 47.1 +/- 6.8 mmHg; pentobarbital/fentanyl-droperidol, 46.9 +/- 3.2 mmHg; diazepam/alphaxalone-alphadolone, 47.8 +/- 4.8 mmHg; chloralose-urethane, 51.0 +/- 1.2 mmHg). Under diazepam/alphaxalone-alphadolone and chloralose-urethane, respiration was depressed and blood gas levels deviated from normal to the extent that artificial ventilation would be necessary to maintain an adequate physiological state.     

Endotoxemia stimulates skeletal muscle Na+-K+-ATPase and raises blood lactate under aerobic conditions in humans

We assessed the hypothesis that the epinephrine surge present during sepsis accelerates aerobic glycolysis and lactate production by increasing activity of skeletal muscle Na(+)-K(+)-ATPase. Healthy volunteers received an intravenous bolus of endotoxin or placebo in a randomized order on two different days. Endotoxemia induced a response resembling sepsis. Endotoxemia increased plasma epinephrine to a maximum at t = 2 h of 0.7 +/- 0.1 vs. 0.3 +/- 0.1 nmol/l (P < 0.05, n = 6-7). Endotoxemia reduced plasma K(+) reaching a nadir at t = 5 h of 3.3 +/- 0.1 vs. 3.8 +/- 0.1 mmol/l (P < 0.01, n = 6-7), followed by an increase to placebo level at t = 7-8 h. During the declining plasma K(+), a relative accumulation of K(+) was seen reaching a maximum at t = 6 h of 8.7 +/- 3.8 mmol/leg (P < 0.05). Plasma lactate increased to a maximum at t = 1 h of 2.5 +/- 0.5 vs. 0.9 +/- 0.1 mmol/l (P < 0.05, n = 8) in association with increased release of lactate from the legs. These changes were not associated with hypoperfusion or hypoxia. During the first 24 h after endotoxin infusion, renal K(+) excretion was 27 +/- 7 mmol, i.e., 58% higher than after placebo. Combination of the well-known stimulatory effect of catecholamines on skeletal muscle Na(+)-K(+)-ATPase activity, with the present confirmation of an expected Na(+)-K(+)- ATPase-induced decline in plasma K(+), suggests that the increased lactate release was due to increased Na(+)-K(+)-ATPase activity, supporting our hypothesis. Thus increased lactate levels in acutely and severely ill patients should not be managed only from the point of view that it reflects hypoxia.     

Role of nitric oxide in the regulation of glucose kinetics in response to endotoxin in dogs.

The purpose of the present in vivo study was to determine the role of nitric oxide (NO) in the regulation of glucose metabolism in response to endotoxin by blocking NO synthesis with N(G)-monomethyl-L-arginine (L-NMMA). In five dogs, the appearance and disappearance rates of glucose (by infusion of [6,6-(2)H(2)]glucose), plasma glucose concentration, and plasma hormone concentrations were measured on five different occasions: saline infusion, endotoxin alone (E coli, 1.0 microg/kg i.v.), and endotoxin administration plus three different doses of primed, continuous infusion of L-NMMA. Endotoxin increased rate of appearance of glucose from 13.7 +/- 1.6 to 23.6 +/- 3.3 micromol x kg(-1) x min(-1) (P < 0.05), rate of disappearance of glucose from 13.9 +/- 1.1 to 24.8 +/- 3.1 micromol x kg(-1) x min(-1) (P < 0.001), plasma lactate from 0.5 +/- 0.1 to 1.7 +/- 0.1 mmol/l (P < 0.01), and counterregulatory hormone concentrations. L-NMMA did not affect the rise in rate of appearance and disappearance of glucose, plasma lactate, or the counterregulatory hormone response to endoxin. Plasma glucose levels were not affected by endotoxin with or without L-NMMA. In conclusion, in vivo inhibition of NO synthesis by high doses of L-NMMA does not affect glucose metabolism in response to endotoxin, indicating that NO is not a major mediator of glucose metabolism during endotoxemia in dogs.     

Interference of the PAF-acether antagonist BN 52021 with endotoxin-induced hypotension in the guinea-pig

Because of the potential role of PAF-acether in the pathogenesis of endotoxin shock, we examined the preventive and curative effects of BN 52021, a new PAF-acether antagonist in guinea-pig challenged with S. Typhimurium endotoxin. A biphasic reduction of mean arterial pressure was elicited by i.v. endotoxin (300 micrograms/kg) in control animals, with a rapid drop of blood pressure (maximal decrease within 10 min), partial recovery at 20 min and a second gradual decrease after 30 min. Treatment with BN 52021 injected 15 min prior to endotoxin reduced the initial rapid drop of blood pressure from 38.5 +/- 5 mmHg in vehicle-treated controls (n = 15) to 17 +/- 3 mmHg (p less than 0.01) in animals treated with 1 mg/kg BN 52021(n = 10) and to 9.5 +/- 8 mmHg (p less than 0.01) in guinea-pigs treated with 6 mg/kg BN 52021 (n = 5). The early hypotensive phase was associated with severe thrombocytopenia-leukopenia; only the thrombocytopenia was reduced by BN 52021. The prolonged secondary phase of hypotension was reduced by BN 52021 pretreatment whereas a small increase of hematocrit persisted. The two phases of the arterial pressure profile during endotoxic shock were not observed in animals previously made thrombopenic by rabbit and anti-platelet serum and only the late hypotensive phase persisted. This late hypotension induced by endotoxin in thrombopenic animals was suppressed by BN 52021 pretreatment suggesting that BN 52021 may act via a platelet-independent mechanism. The intravenous injection of BN 52021 during the prolonged secondary phase of shock was followed by an immediate increase of the depressed blood pressure. This increase of blood pressure was dose-dependent, maximum at 6 mg/kg BN 52021, and observed in normal and thrombopenic animals. The interference of BN 52021 with endotoxin shock may be related to its PAF-acether antagonist properties and suggests that PAF-acether is an important participant in endotoxic shock.     

Hepatic lactate uptake versus leg lactate output during exercise in humans.

The exponential rise in blood lactate with exercise intensity may be influenced by hepatic lactate uptake. We compared muscle-derived lactate to the hepatic elimination during 2 h prolonged cycling (62 +/- 4% of maximal O(2) uptake, (.)Vo(2max)) followed by incremental exercise in seven healthy men. Hepatic blood flow was assessed by indocyanine green dye elimination and leg blood flow by thermodilution. During prolonged exercise, the hepatic glucose output was lower than the leg glucose uptake (3.8 +/- 0.5 vs. 6.5 +/- 0.6 mmol/min; mean +/- SE) and at an arterial lactate of 2.0 +/- 0.2 mM, the leg lactate output of 3.0 +/- 1.8 mmol/min was about fourfold higher than the hepatic lactate uptake (0.7 +/- 0.3 mmol/min). During incremental exercise, the hepatic glucose output was about one-third of the leg glucose uptake (2.0 +/- 0.4 vs. 6.2 +/- 1.3 mmol/min) and the arterial lactate reached 6.0 +/- 1.1 mM because the leg lactate output of 8.9 +/- 2.7 mmol/min was markedly higher than the lactate taken up by the liver (1.1 +/- 0.6 mmol/min). Compared with prolonged exercise, the hepatic lactate uptake increased during incremental exercise, but the relative hepatic lactate uptake decreased to about one-tenth of the lactate released by the legs. This drop in relative hepatic lactate extraction may contribute to the increase in arterial lactate during intense exercise.     

Endotoxin-induced liver hypoxia: defective oxygen delivery versus oxygen consumption.

In vivo EPR was used to investigate liver oxygenation in a hemodynamic model of septic shock in mice. Oxygen-sensitive material was introduced either (i) as a slurry of fine particles which localized at the liver sinusoids (pO2 = 44.39 +/- 5.13 mmHg) or (ii) as larger particles implanted directly into liver tissue to measure average pO2 across the lobule (pO2 = 4.56 +/- 1.28 mmHg). Endotoxin caused decreases in pO2 at both sites early (5-15 min) and at late time points (6 h after endotoxin; sinusoid = 11.22 +/- 2.48 mmHg; lobule = 1.16 +/- 0.42 mmHg). The overall pO2 changes observed were similar (74.56% versus 74.72%, respectively). Blood pressures decreased transiently between 5 and 15 min (12.88 +/- 8% decrease) and severely at 6 h (59 +/- 9% decrease) following endotoxin, despite volume replacement with saline. Liver and circulatory nitric oxide was elevated at these times. Liver oxygen extraction decreased from 44% in controls to only 15% following endotoxin, despite severe liver hypoxia. Arterial oxygen saturation, blood flow (hepatic artery), and cardiac output were unaffected. Pretreatment with l-NMMA failed to improve endotoxin-induced oxygen defects at either site, whereas interleukin-13 preserved oxygenation. These site-specific measurements of pO2 provide in vivo evidence that the principal cause of liver hypoxia during hypodynamic sepsis is reduced oxygen supply to the sinusoid and can be alleviated by maintaining sinusoidal perfusion.     

Increased lactate appearance and reduced clearance during hypoxia in dogs

In order to assess the effects of severe hypoxia on whole body glucose and lactate kinetics, nine experiments were performed on anesthetized, ventilated mongrel dogs. [U-13C]glucose and [1-14C]lactate (n = 5), or [6-14C]glucose and [U-13C]lactate (n = 4) were infused using the primed-continuous infusion method. Cardiac output was measured by thermodilution. After a control period with 21% O2, inspired O2 was reduced for 90 minutes. Three of the experiments resulted in unstable hemodynamics and lactate levels, and are excluded from the mean data. Arterial PO2 fell from a control level of 106.8 +/- 11.9 to 24.2 +/- 3.5 mmHg during the last 45 minutes of hypoxia, and O2 transport fell to 52% of normoxic values. Arterial lactate concentration and the rate of appearance increased by 428% and 182%, respectively, from control to hypoxia. The metabolic clearance rate for lactate fell by 34%. Arterial glucose levels did not change significantly with hypoxia, but the rate of glucose disappearance rose by 70%, and the rate of glucose conversion to lactate increased 3-fold. It is concluded that acute severe hypoxia in anesthetized dogs causes 1) a large increase in arterial lactate levels, but no significant change in glycemia, 2) a large increase in the rate of lactate disappearance and only a small increase in the rate of glucose disappearance and 3) a fall in the metabolic clearance rate of lactate.     

Changes to metabolite concentration in fetal sheep subjected to prolonged hypobaric hypoxia

The effect of hypobaric hypoxaemia on the concentration of metabolic substrates in the ovine fetus and pregnant ewe with implanted vascular catheters, was investigated. At 120 to 141 days of gestation sheep were subjected to hypobaria (mean fetal carotid PO2 12.7 +/- 0.7 torr; n = 9) or normobaria (mean fetal carotid PO2 22.7 +/- 0.7 torr; n = 11; P less than 0.001). At 141 days gestation mean fetal weight was 3.46 +/- 0.72 kg in the hypobaric group compared to 4.15 +/- 0.51 in the normobaric group (P less than 0.05). Concentrations of glucose in maternal and fetal plasma and fructose in fetal plasma were similar in hypobaric and normobaric fetuses. The concentration of lactate in fetal plasma rose from 1.68 +/- 1.34 to 8.79 +/- 5.8 mmol/l (P less than 0.001) within 24 h of onset of hypoxia, but fell to 3.36 +/- 1.13 mmol/l by day 3 of treatment, though still significantly above the concentration of lactate in the control fetuses (1.47 +/- 0.47; P less than 0.001). There was no significant effect of hypoxia on the concentration of lactate or alanine in maternal plasma. Alanine concentration in the plasma of fetuses subjected to hypoxia significantly increased within 24 h of exposure (0.28 +/- 0.10 vs 0.58 +/- 0.39 mmol/l; P less than 0.01) and remained elevated for the duration of the study. There was no significant effect of gestational age on the concentration of metabolic substrates in either the control or experimental groups. Hypoxia is associated with a sustained rise in the concentration of plasma lactate and alanine in the fetus.(ABSTRACT TRUNCATED AT 250 WORDS)     

Endotoxin-induced alterations in hepatic glucose-6-phosphatase activity and gene expression

The mechanisms responsible for the glycemic changes associated with endotoxic shock are not fully understood, but are known to involve the ability of the liver to produce glucose. The purpose of the present study was to determine whether endotoxin (LPS) influences the expression and activity of glucose-6-phosphatase (Glu-6-Pase) during the early hyperglycemic phase and the later hypoglycemic phase. Rats were injected with a relatively large dose of LPS (20 mg/kg) or saline (control), and sacrificed at 1 or 5 h post-injection. Both the plasma glucose concentration and glucose production were elevated 1 h post-LPS (2-fold) and both decreased at 5 h postinjection (50%). Compared to time-matched control values, hepatic glucose-6-phosphate and fructose-6-phosphate levels were significantly decreased at both 1 and 5 h. Hepatic Glu-6-Pase activity and mRNA levels were moderately increased, 1 h after injection of LPS. At 5 h, an 88% decrease in mRNA abundance for Glu-6-Pase was associated with a 30% decrease in activity of this enzyme. Plasma insulin concentrations were not different 1 h after LPS and were elevated 2-fold from control values at 5 h. Circulating levels of glucagon and corticosterone were elevated at both time points following LPS. Our data indicate that the LPS-induced hypoglycemia and reduction in hepatic glucose production were accompanied by a depression in Glu-6-Pase activity and gene expression.     

Effect of insulin on gluconeogenesis and the metabolism of lactate in sheep

Owing to the fermentative nature of their digestion, ruminant animals are highly dependent upon gluconeogenesis to meet their glucose needs. The role of hormones in regulating this process is not clear. The purpose of this study was to examine the effect of insulin on the utilization of lactate in glucose synthesis in sheep. The euglycemic model was used in sheep. [U-14C]Lactate and [6-3H]glucose were infused to monitor lactate and glucose fluxes. Hepatic metabolism was measured using radioisotopic and venoarterial concentration difference techniques. Insulin concentrations increased from basal concentrations of 16 +/- 2 to 95 +/- 9 microU/mL. Insulin reduced the net hepatic utilization of lactate (303 +/- 43 vs. 120 +/- 27 mumol/min), hepatic extraction efficiency of lactate (29 +/- 4 vs. 9 +/- 2%), hepatic output of glucose (338 +/- 33 vs. 103 +/- 21 mumol/min), and incorporation of lactate into glucose (90 +/- 5 vs. 46 +/- 8 mumol/min). Insulin at physiological levels can inhibit hepatic gluconeogenesis in ruminants.     

Arginine vasopressin reduces intestinal oxygen supply and mucosal tissue oxygen tension

We investigated intestinal oxygen supply and mucosal tissue PO2 during administration of increasing dosages of continuously infused arginine vasopressin (AVP) in an autoperfused, innervated jejunal segments in anesthetized pigs. Mucosal tissue PO2 was measured by employing two Clark-type surface oxygen electrodes. Oxygen saturation of jejunal microvascular hemoglobin was determined by tissue reflectance spectrophotometry. Microvascular blood flow was assessed by laser-Doppler velocimetry. Systemic hemodynamic variables, mesenteric venous and systemic acid-base and blood gas variables, and lactate measurements were recorded. Measurements were performed at baseline and at 20-min intervals during incremental AVP infusion (n = 8; 0.007, 0.014, 0.029, 0.057, 0.114, and 0.229 IU.kg(-1).h(-1), respectively) or infusion of saline (n=8). AVP infusion led to a significant (P < .05), dose-dependent decrease in cardiac index (from 121 +/- 31 to 77 +/- 27 ml.kg(-1).min(-1) at 0.229 IU.kg(-1).h(-1)) and systemic oxygen delivery (from 14 +/- 3 to 9 +/- 3 ml.kg(-1).min(-1) at 0.229 IU.kg(-1).h(-1)) concomitant with an increase in systemic oxygen extraction ratio (from 31 +/- 4 to 48 +/- 10%). AVP decreased microvascular blood flow (from 133 +/- 47 to 82 +/- 35 perfusion units at 0.114 IU.kg(-1).h(-1)), mucosal tissue PO2 (from 26 +/- 7 to 7 +/- 2 mmHg at 0.229 IU.kg(-1).h(-1)), and microvascular hemoglobin oxygen saturation (from 51 +/- 9 to 26 +/- 12% at 0.229 IU.kg(-1).h(-1)) without a significant increase in mesenteric venous lactate concentration (2.3 +/- 0.8 vs. 3.4 +/- 0.7 mmol/l). We conclude that continuously infused AVP decreases intestinal oxygen supply and mucosal tissue PO2 due to a reduction in microvascular blood flow and due to the special vascular supply in the jejunal mucosa in a dose-dependent manner in pigs.     

Ability of insulin to modulate hepatic glucose production in aging rats is impaired by fat accumulation

Increased total fat mass (FM) and visceral fat (VF) may account in part for age-associated decrease in hepatic insulin action. This study determined whether preventing the changes in body fat distribution abolished this defect throughout aging. We studied the F(1) hybrid of Brown Norway-Fischer 344 rats (n = 29), which we assigned to caloric restriction (CR) or fed ad libitum (AL). CR (55% of the calories consumed by AL) was initiated and used at 2 mo to prevent age-dependent increases in FM and VF. AL rats were studied at 2, 8, and 20 mo; CR rats were studied at 8 and 20 mo. VF and FM remained unchanged throughout aging in CR rats. AL-fed rats at 8 and 20 mo had over fourfold higher FM and VF compared with both CR groups. Insulin clamp studies (3 mU. kg(-1). min(-1) with somatostatin) were performed to assess hepatic insulin sensitivity. Prevention of fat accretion resulted in a marked improvement in insulin action in the suppression of hepatic glucose production (HGP) (6.3 +/- 0.3 and 7.2 +/- 1.2 mg. kg(-1). min(-1) in 8- and 20-mo CR rats vs. 8.3 +/- 0.5 and 10.8 +/- 0.9 mg. kg(-1). min(-1) in 8- and 20-mo AL rats, respectively). The rate of gluconeogenesis (by enrichment of hepatic uridine diphosphate glucose and phosphoenolpyruvate pools by [(14)C]lactate) was unchanged in all groups. The improvement in hepatic insulin action in the CR group was mostly due to effective suppression of glycogenolysis (4.4 +/- 0.3 and 4.9 +/- 0.3 mg. kg(-1). min(-1) in 8- and 20-mo CR rats vs. 5.8 +/- 0.6 and 8.2 +/- 1.0 mg. kg(-1). min(-1) in 8- and 20-mo AL rats, respectively). The results demonstrated the preservation of hepatic insulin action in aging CR rats. Therefore, body fat and its distribution are major determinants of age-associated hepatic insulin resistance.     

Quantitation of gluconeogenesis by (2)H nuclear magnetic resonance analysis of plasma glucose following ingestion of (2)H(2)O

We present a simple (2)H NMR assay of the fractional contribution of gluconeogenesis to hepatic glucose output following ingestion of (2)H(2)O. The assay is based on the measurement of relative deuterium enrichment in hydrogens 2 and 3 of plasma glucose. Plasma glucose was enzymatically converted to gluconate, which displays fully resolved deuterium 2 and 3 resonances in its (2)H NMR spectrum at 14.1 T. The signal intensity of deuterium 3 relative to deuterium 2 in the gluconate derivative as quantitated by (2)H NMR was shown to provide a precise and accurate measurement of glucose enrichment in hydrogen 3 relative to hydrogen 2. This measurement was used to estimate the fractional contribution of gluconeogenesis to hepatic glucose output for two groups of rats; one group was fasted for 7 h and the other was fasted for 29 h. Rats were administered (2)H(2)O to enrich total body water to 5% over the last 4-5 h of each fasting period. For the 7-h fasted group, the hydrogen 3/hydrogen 2 enrichment ratio of plasma glucose was 0.32 +/- 0.09 (n = 7). This indicates that gluconeogenesis contributed 32 +/- 9% of total hepatic glucose output with glycogenolysis contributing the remainder. For the 29-h fasted group, the hydrogen 3/hydrogen 2 enrichment ratio of plasma glucose was 0.81 +/- 0.10 (n = 6), indicating that gluconeogenesis supplied the bulk of hepatic glucose output (81 +/- 10%).