Biomedical subjects

D B Lacy

Publications and source records attributed to D B Lacy.

At least 37 records · Page 2Linked to original sources

PubMed1998

Alterations in hepatic gluconeogenic amino acid uptake and gluconeogenesis in the endotoxin treated conscious dog.

We examined the effect of a 240 min intraportal infusion of a nonlethal dose of Escherichia coli endotoxin (.21 g x kg(-1) x min[-1]) on hepatic amino acid and glucose metabolism in chronically catheterized 42 h fasted conscious dogs (n = 8). Hepatic metabolism was assessed using tracer (3-[3H]glucose [U-14C]alanine) and arteriovenous difference techniques. After endotoxin administration net hepatic glucose output increased twofold. Arterial plasma insulin levels decreased by 25%, whereas arterial plasma glucagon and cortisol levels increased 10- and 6-fold, respectively. Arterial lactate levels increased 6.4-fold, whereas net hepatic lactate uptake was not increased. Arterial alanine levels (1.6-fold) and net hepatic alanine uptake (1.3-fold) increased, whereas net hepatic alanine fractional extraction was unaltered. In contrast, the arterial levels of the other gluconeogenic amino acids (glutamine, glycine, serine, and threonine) decreased. Despite this decrease, net uptake of these amino acids by the liver did not decrease, because net hepatic amino acid fractional extraction increased. Total net hepatic gluconeogenic precursor uptake was unaltered (1.1 +/- .1 to 1.3 +/- .3 mg x kg(-1) x min(-1) expressed in glucose equivalents). In summary, gluconeogenesis does not increase after endotoxin administration. Thus, an increase in net hepatic glycogenolysis accounts for the majority of the increase in hepatic glucose production. The lack of an increase in alanine fractional extraction, despite hyperglucagonemia and a rise in the fractional extraction of other gluconeogenic amino acids, suggests that endotoxin specifically impairs hepatic alanine entry in vivo.

Amino Acids↗

PubMed1998

Regulation of hepatic glutamine metabolism during exercise in the dog.

The goal of this study was to determine how liver glutamine (Gln) metabolism adapts to acute exercise in the 18-h-fasted dogs (n = 7) and in dogs that were glycogen depleted by a 42-h fast (n = 8). For this purpose, sampling (carotid artery, portal vein, and hepatic vein) and infusion (vena cava) catheters and Doppler flow probes (portal vein, hepatic artery) were implanted under general anesthesia. At least 16 days later an experiment, consisting of a 120-min equilibration period, a 30-min basal sampling period, and a 150-min exercise period was performed. At the start of the equilibration period, a constant-rate infusion of [5-15N]Gln was initiated. Arterial Gln flux was determined by isotope dilution. Gut and liver Gln release into and uptake from the blood were calculated by combining stable isotopic and arteriovenous difference methods. The results of this study show that 1) in the 18-h-fasted dog, approximately 10% and approximately 35% of the basal Gln appearance in arterial blood is due to Gln release from the gut and liver, respectively, whereas approximately 30% and approximately 25% of the basal Gln disappearance is due to removal by these tissues; 2) extending the fast to 42 h does not affect basal arterial Gln flux or the contribution of the gut to arterial Gln fluxes but decreases hepatic Gln release, causing a greater retention of gluconeogenic carbon by the liver; 3) moderate-intensity exercise increases hepatic Gln removal from the blood regardless of fast duration but does not affect the hepatic release of Gln; and 4) Gln plays an important role in channeling nitrogen into the ureagenic pathway in the basal state, and this role is increased by approximately 80% in response to exercise. These studies illustrate the quantitative importance of the splanchnic bed contribution to arterial Gln flux during exercise and the ability of the liver to acutely adapt to changes in metabolic requirements induced by the combined effects of fasting and exercise.

Animals↗

PubMed1998

Hepatic and muscle glucose metabolism during total parenteral nutrition: impact of infection.

We examined the impact of infection on hepatic and muscle glucose metabolism in dogs adapted to chronic total parenteral nutrition (TPN). Studies were done in five conscious chronically catheterized dogs, in which sampling (artery, portal and hepatic vein, and iliac vein), infusion catheters (inferior vena cava), and Transonic flow probes (hepatic artery, portal vein, and iliac artery) were implanted. Fourteen days after surgery, dogs were placed on TPN. After 5 days of TPN, an infection was induced, and the TPN was continued. The balance of substrates across the liver and limb was assessed on the day before infection (day 0) and 18 (day 1) and 42 h (day 2) after infection. On day 0, the liver was a marked net consumer of glucose (4.3 +/- 0.6 mg. kg-1. min-1) despite near normoglycemia (117 +/- 5 mg/dl) and only mild hyperinsulinemia (16 +/- 2 microU/ml). In addition, the majority (79 +/- 13%) of the glucose taken up by the liver was released as lactate (34 +/- 6 micromol. kg-1. min-1). After infection, net hepatic glucose uptake decreased markedly on day 1 (1.6 +/- 0.9 mg. kg-1. min-1) and remained suppressed on day 2 (2.4 +/- 0.5 mg. kg-1. min-1). Net hepatic lactate output also decreased on days 1 and 2 (15 +/- 5 and 12 +/- 3 micromol. kg-1. min-1, respectively). This occurred despite increases in arterial plasma glucose on days 1 and 2 (135 +/- 9 and 144 +/- 9 mg/dl, respectively) and insulin levels on days 1 and 2 (57 +/- 14 and 34 +/- 9 microU/ml, respectively). In summary, the liver undergoes a profound adaptation to TPN, making it a major site of glucose disposal and conversion to lactate. Infection impairs hepatic glucose uptake, forcing TPN-derived glucose to be removed by peripheral tissues.

Animals↗

PubMed1998

Hepatic production and intestinal uptake of IGF-I: response to infection.

The role of the liver and gut in contributing to the infection-induced fall in circulating insulin-like growth factor I (IGF-I) was examined in chronically catheterized conscious dogs. Two weeks before study, catheters and Doppler flow probes were implanted to assess hepatic and gut balance of IGF-I. To control nutrient intake, dogs were placed on total parenteral nutrition (TPN) as their sole caloric source. After dogs received TPN for 5 days, net hepatic and intestine IGF-I balances were assessed. A hypermetabolic infected state was then induced by the intraperitoneal implantation of a fibrin clot containing Escherichia coli. TPN was continued, and organ IGF-I balance was assessed 24 and 48 h after induction of infection. Arterial IGF-I levels were significantly decreased following infection (111 +/- 18, 62 +/- 10, and 63 +/- 8 ng/ml before and 24 and 48 h after, respectively). Net hepatic IGF-I output decreased markedly (221 +/- 73, to 73 +/- 41 and 41 +/- 17 ng. kg-1. min-1 before and 24 and 48 h after, respectively). The infection-induced decrease in hepatic IGF-I output could not be explained by concomitant alterations in plasma cortisol or insulin levels. The gut demonstrated a net uptake of IGF-I before infection (178 +/- 29 ng. kg-1. min-1). However, after infection, intestinal IGF-I uptake was completely suppressed (-10 +/- 15 and -8 +/- 36 ng. kg-1. min-1). In summary, infection decreases net hepatic IGF-I release 65-80% and completely suppresses net IGF-I uptake by the intestine. As a consequence of these reciprocal changes in IGF-I balance across the liver and intestine, splanchnic production of IGF-I was unchanged by infection. These data suggest that changes in the clearance and/or production of IGF-I by extrasplanchnic tissues contribute to the infection-induced decrease in circulating IGF-I levels.

Animals↗

PubMed1998

Enhanced muscle glucose uptake facilitates nitrogen efflux from exercised muscle.

The hypothesis that glucose ingestion in the postexercise state enhances the synthesis of glutamine and alanine in the skeletal muscle was tested. Glucose was infused intraduodenally for 150 min (44.5 micromol . kg-1 . min-1) beginning 30 min after a 150-min period of exercise (n = 7) or an equivalent duration sedentary period (n = 10) in 18-h-fasted dogs. Prior exercise caused a twofold greater increase in limb glucose uptake during the intraduodenal glucose infusion compared with uptake in sedentary dogs. Arterial glutamine levels fell gradually with the glucose load in both groups. Net hindlimb glutamine efflux increased in response to intraduodenal glucose in exercised but not sedentary dogs (P < 0. 05-0.01). Arterial alanine levels, depleted by 50% with exercise, rose with intraduodenal glucose in exercised but not sedentary dogs (P < 0.05-0.01). Net hindlimb alanine efflux also rose in exercised dogs in response to intraduodenal glucose (P < 0.05-0.01), whereas it was not different from baseline in sedentary controls for the first 90 min of glucose infusion. Beyond this point, it, too, rose significantly. We conclude that oral glucose may facilitate recovery of muscle from prolonged exercise by enhancing the removal of nitrogen in the form of glutamine and alanine.

Alanine↗

PubMed1997

Recombinant expression and purification of the botulinum neurotoxin type A translocation domain.

Botulinum neurotoxin type A in its fully activated form exists as a dichain protein consisting of a 50-kDa light chain and a 100-kDa heavy chain linked by a disulfide bond (B. R. DasGupta and H. Sugiyama, Biochem. Biophys. Res. Commun. 48, 108-112, 1972). The protein can be further subdivided into three functional domains: a catalytic domain corresponding to the light chain, a translocation domain associated with the N-terminal half of the heavy chain, and a binding domain as the C-terminal half. To facilitate further structural and functional studies on the mechanism of toxin translocation, we report here the recombinant Escherichia coli expression and purification of the isolated translocation domain with a yield of 1 mg pure protein per 1 g cell paste. Circular dichroism, enzyme-linked immunosorbent assays, and preliminary crystallization experiments verify proper protein folding. This reagent should serve as a key tool in elucidating the mechanism of translocation and in determining how the catalytic domain, a large 50-kDa metalloprotease, is delivered to the cytosol.

Biological Transport↗

PubMed1997

Sympathetic drive to liver and nonhepatic splanchnic tissue during prolonged exercise is increased in diabetes.

This study was conducted to assess whether nonhepatic splanchnic (NHS) and hepatic tissues contribute to the increase in circulating norepinephrine during prolonged exercise, and to determine whether such a response is exaggerated during exercise in the poorly controlled diabetic when the arterial norepinephrine response is excessive. Chronically catheterized (carotid artery, portal vein, and hepatic vein) and instrumented (Doppler flow probes on hepatic artery and portal vein) normal (n = 6) and alloxan-diabetic (n = 5) dogs were studied during rest (30 minutes) and moderate treadmill exercise (150 minutes). Basal plasma glucose of diabetic dogs was threefold that of control dogs. Since epinephrine is not released by splanchnic tissues, NHS and hepatic epinephrine fractional extraction (FX) can be accurately measured. Because epinephrine FX = norepinephrine FX, norepinephrine spillover can be calculated. NHS and hepatic epinephrine FX remained stable during rest and exercise in both control and diabetic dogs. Although basal NHS norepinephrine spillover was not different between the two groups, basal hepatic norepinephrine spillover was lower in the controls (1.1 +/- 0.3 ng/kg . min) compared with the diabetics (3.6 +/- 1.1 ng/kg . min). Although NHS norepinephrine spillover increased with exercise in the normal dog (3.1 +/- 0.6 ng/kg . min at t = 150 minutes), there was no increase in hepatic norepinephrine spillover (1.1 +/- 0.3 ng/kg . min at t = 150 minutes). In contrast, NHS (8.8 +/- 1.6 ng/kg . min at t = 150 minutes) and hepatic (6.9 +/- 1.8 ng/kg . min at t = 150 minutes) norepinephrine spillover were both markedly increased in the diabetic dog to rates approximately threefold and sixfold higher than in the normal dog. These data show that an increase in NHS but not hepatic norepinephrine spillover is a component of the normal response to prolonged exercise. The exaggerated increase in arterial norepinephrine during exercise in the diabetic state is due, in part, to both increased sympathetic drive to the gut and liver. This increase in sympathetic drive to the splanchnic bed may contribute to the deleterious effects of exercise in poorly controlled diabetes.

Animals↗

PubMed1997

Interaction of exercise, insulin, and hypoglycemia studied using euglycemic and hypoglycemic insulin clamps.

Hyperinsulinemic euglycemic and hypoglycemic clamps were used to study the interaction of exercise, insulin, and hypoglycemia at rest and during exercise in the dog. Sampling (artery and portal, hepatic, and iliac veins) and infusion (vena cava) catheters and a flow probe (external iliac artery) were implanted surgically >16 days before study. After an 18-h fast and an 80-min tracer equilibration period, dogs were studied in the basal state (t = -40 to 0 min) and during a moderate treadmill exercise (t = 0-150 min) period or an equivalent duration sedentary period. Insulin was infused at 1 mU x kg(-1) x min(-1) from t = 0-150 min. In one group of sedentary (n = 7) and one group of exercised (n = 6) dogs, glucose was clamped at basal during the insulin infusion. In another group of sedentary (n = 6) and another group of exercised (n = 6) dogs, arterial glucose was clamped at hypoglycemic levels (approximately 65 mg/dl) during the insulin infusion. Arteriovenous difference and isotopic ([3-(3)H]glucose, [U-(14)C]glucose) techniques were used to assess glucose metabolism. Insulin levels were approximately 40 microU/ml in all groups. Data show that 1) counterregulatory hormone (glucagon, catecholamines, and cortisol) responses to exercise and hypoglycemia combined are synergistically higher than the response to either stimulus alone; 2) exercise-induced increases in insulin action are negated during hypoglycemia by the counterregulatory response; 3) decreased need for exogenous glucose during hypoglycemic compared with euglycemic exercise is due to stimulation of endogenous glucose production, which accounts for approximately 30% of the decrease, and reduction of glucose utilization, which accounts for approximately 70%; and 4) insulin-stimulated nonoxidative glucose metabolism is unaffected by exercise or hypoglycemia, whereas insulin-stimulated oxidative glucose metabolism is selectively increased by exercise and decreased by hypoglycemia. In conclusion, the marked rise in insulin action during exercise is matched, under insulin-induced hypoglycemic conditions, by an equally profound increase in counterregulation. The effectiveness of the potent insulin counterregulatory response may be important in decreasing the magnitude and frequency of exercise-induced hypoglycemia.

Animals↗

PubMed1997

Role of hepatic alpha- and beta-adrenergic receptor stimulation on hepatic glucose production during heavy exercise.

The role of catecholamines in the control of hepatic glucose production was studied during heavy exercise in dogs, using a technique to selectively block hepatic alpha- and beta-adrenergic receptors. Surgery was done > 16 days before the study, at which time catheters were implanted in the carotid artery, portal vein, and hepatic vein for sampling and the portal vein and vena cava for infusions. In addition, flow probes were implanted on the portal vein and hepatic artery. Each study consisted of a 100-min equilibration, a 30-min basal, a 20-min heavy exercise (approximately 85% of maximum heart rate), a 30-min recovery, and a 30-min adrenergic blockade test period. Either saline (control; n = 7) or alpha (phentolamine)- and beta (propranolol)-adrenergic blockers (Blk; n = 6) were infused in the portal vein. In both groups, epinephrine (Epi) and norepinephrine (NE) were infused in the portal vein during the blockade test period to create supraphysiological levels at the liver. Isotope ([3-3H]glucose) dilution and arteriovenous differences were used to assess hepatic function. Arterial Epi, NE, glucagon, and insulin levels were similar during exercise in both groups. Endogenous glucose production (Ra) rose similarly during exercise to 7.9 +/- 1.2 and 7.5 +/- 2.0 mg.kg-1.min-1 in control and Blk groups at time = 20 min. Net hepatic glucose output also rose to a similar rate in control and Blk groups with exercise. During the blockade test period, arterial plasma glucose and Ra rose to 164 +/- 5 mg/dl and 12.0 +/- 1.4 mg.kg-1.min-1, respectively, but were essentially unchanged in Blk. The attenuated response to catecholamine infusion in Blk substantiates the effectiveness of the hepatic adrenergic blockade. In conclusion, these results show that direct hepatic adrenergic stimulation does not participate in the increase in Ra, even during the exaggerated sympathetic response to heavy exercise.

Adrenergic alpha-Antagonists↗

PubMed1997

Effect of physical activity and fasting on gut and liver proteolysis in the dog.

The aim of this study was to determine how gut and liver protein kinetics adapt to acute exercise in the 18-h-fasted dog (n = 7) and in dogs glycogen depleted by a 42-h fast (n = 8). For this purpose, sampling (artery and portal and hepatic veins) and infusion (vena cava) catheters and Doppler flow probes (portal vein and hepatic artery) were implanted with animals under general anesthesia. At least 16 days later, an experiment, consisting of a 120-min equilibration period, a 30-min basal sampling period, and a 150-min exercise period, was performed. At the start of the equilibration period, a constant rate infusion of [1-13C]leucine was initiated. Gut and liver leucine appearance and disappearance rates were calculated in these studies by combining a novel stable isotopic method and arteriovenous difference methods. In the determination of tissue leucine kinetics the tissue inflow of both alpha-[13C]ketoisocaproic acid and [13C]leucine was taken into account. The results of this study show that 1) the splanchnic bed (liver plus gut) contributes approximately 40% to the whole body proteolytic rate in the basal state and during exercise in dogs fasted for either 18 or 42 h, 2) the contributions of the gut and liver to splanchnic bed proteolysis is about equal in the basal state in both 18- and 42-h-fasted dogs, and 3) exercise in the 18-h-fasted dog leads to a greater emphasis on gut proteolysis and a lesser emphasis on hepatic proteolysis. These studies highlight the important contribution of gut and hepatic proteolysis to whole body proteolysis and the ability of the gut to acutely adapt to changes in physical activity.

Animals↗

PubMed1997

Sympathetic drive to liver and nonhepatic splanchnic tissue during heavy exercise.

The contribution of sympathetic drive and vascular catecholamine delivery to the splanchnic bed during heavy exercise was studied in dogs that underwent a laparotomy during which flow probes were implanted onto the portal vein and hepatic artery and catheters were inserted into the carotid artery, portal vein, and hepatic vein. At least 16 days after surgery, dogs completed a 20-min heavy exercise protocol (mean work rate of 5.7 +/- 1 miles/h, 20 +/- 2% grade). Arterial epinephrine (Epi) and norepinephrine (NE) increased by approximately 500 and approximately 900 pg/ml, respectively, after 20 min of heavy exercise. Because Epi is not released from the splanchnic bed and because Epi fractional extraction (FX) = NE FX, NE uptake by splanchnic tissue can be calculated despite simultaneous release of NE. Basal nonhepatic splanchnic (NHS) FX increased from a basal rate of 0.52 +/- 0.09 to a peak of 0.64 +/- 0.05 at 10 min of exercise. Hepatic Epi FX increased from a basal rate of 0.68 +/- 0.10 to 0.81 +/- 0.09 at 20 min of exercise. Even though NHS extraction of Epi reduced portal vein Epi levels by approximately 60%, the release of NE from NHS tissue maintained portal vein NE at levels similar to those in arterial blood. NHS NE spillover increased from a basal rate of 5.7 +/- 1.4 to 11.7 +/- 2.8 ng x kg(-1) x min(-1) at 20 min of exercise. Hepatic NE spillover increased from a basal rate of 5.0 +/- 1.2 ng x kg(-1) x min(-1) to a peak of 14.2 +/- 2.8 ng x kg(-1) x min(-1) at 15 min of exercise. These results show that 1) approximately two- and threefold increases in NHS and hepatic NE spillover occur during heavy exercise, demonstrating that sympathetic drive to these tissues contributes to the increase in circulating NE; 2) the high catecholamine FX by the NHS tissues results in an Epi level at the liver that is considerably lower than that in the arterial blood; and 3) circulating NE delivery to the liver is sustained despite high catecholamine FX due to simultaneous NHS NE release.

Animals↗

PubMed1997

Gut and liver fat metabolism in depancreatized dogs: effects of exercise and acute insulin infusion.

Excessive circulating fat levels are a defining feature of poor metabolic control in diabetes. Splanchnic adipose tissue is a source of free fatty acids (FFA), and the liver is a key site of FFA utilization and the sole source of ketones. Despite the role of splanchnic tissues in fat metabolism, little is known about how these tissues respond to diabetes under divergent metabolic conditions. Therefore, splanchnic fat metabolism was studied in poorly controlled diabetes under two conditions. First, it was studied during exercise, a stimulus that enhances FFA flux. Second, it was studied while insulin was being acutely infused to achieve levels normally present during exercise, a treatment that may be expected to inhibit lipolysis. For this purpose, liver and gut arteriovenous differences were used during rest and 2.5 h of treadmill exercise in insulin-deficient (n = 6) and acutely insulin-infused (n = 4) depancreatized (PX) dogs. The data show that 1) exercise, in insulin-deficient PX dogs, leads to an increase in net FFA release from mesenteric fat that is equal in magnitude to the response in nondiabetic dogs; 2) net hepatic fractional FFA extraction is increased twofold during exercise in both insulin-deficient PX dogs and nondiabetic control dogs; 3) during exercise, approximately 40 and 75% of the FFA consumed by the liver is effectively transferred from fat stores mobilized from splanchnic adipose tissue in insulin-deficient PX and nondiabetic dogs, respectively; 4) hepatic ketogenic efficiency is elevated during rest three- to fourfold in insulin-deficient PX dogs compared with nondiabetic control dogs and remains elevated during exercise; and 5) surprisingly, acute insulin replacement is ineffective in normalizing net gut, hepatic, or splanchnic FFA or ketone body balances in PX dogs.

Adipose Tissue↗

PubMed1996

Effect of prior exercise on the partitioning of an intestinal glucose load between splanchnic bed and skeletal muscle.

Exercise leads to marked increases in muscle insulin sensitivity and glucose effectiveness. Oral glucose tolerance immediately after exercise is generally not improved. The hypothesis tested by these experiments is that after exercise the increased muscle glucose uptake during an intestinal glucose load is counterbalanced by an increase in the efficiency with which glucose enters the circulation and that this occurs due to an increase in intestinal glucose absorption or decrease in hepatic glucose disposal. For this purpose, sampling (artery and portal, hepatic, and femoral veins) and infusion (vena cava, duodenum) catheters and Doppler flow probes (portal vein, hepatic artery, external iliac artery) were implanted 17 d before study. Overnightfasted dogs were studied after 150 min of moderate treadmill exercise or an equal duration rest period. Glucose ([14C]glucose labeled) was infused in the duodenum at 8 mg/kg x min for 150 min beginning 30 min after exercise or rest periods. Values, depending on the specific variable, are the mean +/- SE for six to eight dogs. Measurements are from the last 60 min of the intraduodenal glucose infusion. In response to intraduodenal glucose, arterial plasma glucose rose more in exercised (103 +/- 4 to 154 +/- 6 mg/dl) compared with rested (104 +/- 2 to 139 +/- 3 mg/dl) dogs. The greater increase in glucose occurred even though net limb glucose uptake was elevated after exercise (35 +/- 5 vs. 20 +/- 2 mg/min) as net splanchnic glucose output (5.1 +/- 0.8 vs. 2.1 +/- 0.6 mg/kg x min) and systemic appearance of intraduodenal glucose (8.1 +/- 0.6 vs. 6.3 +/- 0.7 mg/kg x min) were also increased due to a higher net gut glucose output (6.1 +/- 0.7 vs. 3.6 +/- 0.9 mg/kg x min). Adaptations at the muscle led to increased net glycogen deposition after exercise [1.4 +/- 0.3 vs. 0.5 +/- 0.1 mg/(gram of tissue x 150 min)], while no such increase in glycogen storage was seen in liver [3.9 +/- 1.0 vs. 4.1 +/- 1.1 mg/(gram of tissue x 150 min) in exercised and sedentary animals, respectively]. These experiments show that the increase in the ability of previously working muscle to store glycogen is not solely a result of changes at the muscle itself, but is also a result of changes in the splanchnic bed that increase the efficiency with which oral glucose is made available in the systemic circulation.

Animals↗

PubMed1996

Hepatic release of tumor necrosis factor in the endotoxin-treated conscious dog.

The effects of a 4 h intraportal infusion of Escherichia coli lipopolysaccharide (LPS, .21 mu g/kg/min) on the release of tumor necrosis factor (TNF) by hepatic and nonhepatic splanchnic tissues was assessed in the chronically catheterized conscious dog (n = 7) using arteriovenous difference techniques. TNF levels were measured using both a WEHI-164 cytotoxicity assay (WEHI) and a h-TNF-alpha EIA kit (ELISA; Biosource, Camarillo, CA). Using WEHI, arterial TNF levels increased from 10 + or - 6 pg/mL to a peak of 4667 + or - 1442 pg/mL 100 min after LPS and fell to 443 + or - 199 pg/mL by 240 min. Using ELISA, arterial TNF levels increased from 5 + or - 5 pg/mL to a peak of 12,234 + or - 2046 pg/mL at 100 min and fell to 3511 + or - 991 pg/mL by 240 min. WEHI could not be used to assess organ TNF release due to excessive assay variability. Based upon ELISA, net hepatic TNF output increased from undetectable release at basal to 23.0 + or - 10.7 ng/kg/min at 60 min and returned toward basal by 240 min (4.7 + or - 3.8 ng/kg/min). Net release of TNF by the nonhepatic splanchnic bed was not observed. One compartment analysis of the arterial TNF response indicated that net release of TNF by the liver accounted for the majority of the increase in the arterial TNF levels. In summary, after intraportal LPS infusion, it was determined that 1) both assays predict similar qualitative TNF response, while the quantitative response differs, 2) the liver is the major site of TNF production, and 3) the nonhepatic splanchnic bed is not a net producer of TNF.

Animals↗

PubMed1996

Hyperglucagonemia and hepatic glucose metabolism during infection in the conscious dog.

The chronic and acute roles of hyperglucagonemia in sustaining the increased glucose production observed in the conscious infected dog were examined. Three groups of dogs were studied: a sham group (SHAM; n = 10), an infected group (INFXN; n = 11), and a sham group in which the chronic (42-h) increase in glucagon observed in INFXN was simulated (SimGGN; n = 5). INFXN and SimGGN were studied in the presence of hyperglucagonemia. In addition, glucagon was selectively decreased for 180 min in INFXN by use of somatostatin with basal intraportal insulin replacement and in SimGGN by discontinuing the exogenous glucagon infusion. Tracer and arteriovenous difference techniques were used to assess hepatic glucose metabolism and gluconeogenesis. Whereas the rate of glucose appearance (Ra) was increased by 30% (3.3 +/- 0.1 vs. 2.5 +/- 0.1 mg.kg-1.min-1) in INFXN vs. SHAM, Ra did not increase in SimGGN (2.4 +/- 0.2 mg.kg-1.min-1). In addition, the 30% increase in net hepatic gluconeogenic precursor uptake seen in INFXN did not occur in SimGGN despite an augmented net hepatic alanine fractional extraction (0.62 +/- 0.03 vs. 0.47 +/- 0.05, SimGGN vs. INFXN). With acute removal of hyperglucagonemia, endogenous Ra decreased in SimGGN and INFXN by 1.0 +/- 0.2 and 1.4 +/- 0.3 mg.kg-1.min-1, respectively. Net hepatic alanine fractional extraction in INFXN, leading to a greater rise in arterial blood alanine levels. In summary, chronic hyperglucagonemia alone cannot explain the increase in Ra observed during an infection. The marked hyperglucagonemia seen during infection plays an essential role in sustaining normal net hepatic fractional alanine extraction to compensate for an impairment in glucagon-stimulated hepatic amino acid transport activation.

Alanine↗

PubMed1995

Effect of acute glucagon removal on metabolic response to infection in conscious dog.

This study examined the acute role of glucagon in sustaining the increased hepatic gluconeogenesis observed in the conscious infected dog. After a basal sampling period, arterial glucagon levels were selectively decreased for 180 min by a peripheral infusion of somatostatin and basal intraportal infusion of insulin (GGN deficient; n = 6). In a separate protocol (GGN replaced; n = 5) glucagon was also infused intraportally to maintain the glucagon level at that seen during sepsis. Tracer and arteriovenous difference techniques were used to assess hepatic glucose metabolism and gluconeogenesis. In the GGN-deficient group the arterial plasma glucagon level fell from 416 +/- 49 to 88 +/- 21 pg/ml, whereas in the GGN-replaced group it remained elevated throughout (321 +/- 48 to 248 +/- 22 pg/ml). When glucagon was reduced, endogenous glucose production decreased by 1.6 +/- 0.3 mg.kg-1.min-1, and an exogenous glucose infusion was required to maintain euglycemia. Glucose metabolism remained unaltered when glucagon was replaced. When glucagon was deleted, net hepatic gluconeogenic precursor uptake was not altered. In contrast, the efficiency of gluconeogenesis was decreased by 33% compared with the GGN-replaced group. Liver biopsies taken at the end of the experiment indicated that a diversion of gluconeogenic carbon to glycogen accounted for 50% of the fall in gluconeogenic efficiency. In summary, the basal hyperglucagonemia seen during an infection helps sustain glucose production both through its effects on hepatic glycogen metabolism and on gluconeogenic efficiency.

Animals↗

PubMed1995

Carbohydrate metabolism during exercise: influence of circulating fat availability.

To examine the role of circulating fat in the regulation of carbohydrate metabolism, dogs were studied during rest and 90 min of moderate treadmill exercise with nicotinic acid infused to suppress lipolysis with (+Fat; n = 5) or without (-Fat; n = 5) Intralipid. Isotopic and hindlimb arteriovenous methods were used to assess metabolism. Plasma glucose was similar in both protocols during rest and exercise. Differences in insulin, catecholamines, and cortisol between groups were insignificant. Glucagon was approximately 50% greater during rest and exercise in -Fat. The following values represent those at 30 or 40 min of muscular work because peak responses were seen at these times. Arterial free fatty acid levels were 1,129 +/- 253 and 272 +/- 17 mu eq/l at rest and 756 +/- 145 and 269 +/- 51 mu eq/l with exercise in +Fat and -Fat, respectively. Glucose production was 4.2 +/- 0.3 and 5.0 +/- 0.4 mg.kg-1.min-1 at rest and 8.5 +/- 1.3 and 11.4 +/- 0.6 mg.kg-1.min-1 with exercise in +Fat and -Fat, respectively. Glucose utilization was 4.3 +/- 0.3 and 5.3 +/- 0.2 mg.kg-1.min-1 at rest and 9.2 +/- 1.2 and 12.7 +/- 0.8 mg.kg-1.min-1 with exercise in +Fat and -Fat, respectively. Significant glucose flux differences were present during rest and exercise. Limb glucose uptake rose similarly with exercise in +Fat (29 +/- 7 to 82 +/- 22 mumol/min) and -Fat (28 +/- 7 to 88 +/- 16 mumol/min). Arterial blood lactate was 50-100% greater in -Fat compared with that in +Fat.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1995

Effects of an acute increase in epinephrine and cortisol on carbohydrate metabolism during insulin deficiency.

This study was undertaken to investigate the effects of an acute increase in the plasma epinephrine level, with or without an accompanying increase in the plasma cortisol level, during selective insulin deficiency on glycogenolysis and gluconeogenesis in conscious overnight-fasted dogs. Experiments consisted of an 80-min tracer and dye equilibration period, a 40-min basal period, and a 180-min experimental period. In all protocols, selective insulin deficiency was created during the experimental period by infusing somatostatin peripherally (0.8 micrograms.kg-1.min-1) with basal replacement of glucagon intraportally (0.65 ng.kg-1.min-1). In EPI+SAL (n = 6), an additional infusion of epinephrine (0.04 micrograms.kg-1.min-1) was infused during the experimental period along with saline. In EPI+CORT (n = 6), hydrocortisone (3.0 microgram.kg-1.min-1) was infused in addition to epinephrine during the experimental period. In SAL+CORT (n = 5), hydrocortisone was infused during the experimental period. In SALINE (n = 5), neither epinephrine nor cortisol was infused. [3-3H]glucose, [U-14C]alanine, and indocyanine green dye were used to assess glucose production (rate of appearance [Ra]) and gluconeogenesis using tracer and arteriovenous difference techniques. During selective insulin deficiency in SALINE, the arterial plasma glucose level increased from 6.0 +/- 0.1 to 15.8 +/- 1.1 mmol/l; Ra increased from 14.7 +/- 0.7 to 24.9 +/- 1.7 mumol.kg-1.min-1. Gluconeogenic efficiency and the conversion of alanine and lactate to glucose increased to 300 +/- 55 and 355 +/- 67% of basal. In EPI+SAL and EPI+CORT, plasma glucose increased from 6.2 +/- 0.1 to 19.8 +/- 0.9 mmol/l and from 6.3 +/- 0.1 to 19.5 +/- 0.9 mmol/l. In EPI+SAL and EPI+CORT, Ra increased from 16.5 +/- 1.1 to 29.3 +/- 3.2 mumol.kg-1.min-1 and from 15.4 +/- 1.3 to 28.3 +/- 2.5 mumol.kg-1.min-1. The rise in gluconeogenic efficiency was similar to the rise that occurred in SALINE, but gluconeogenic conversion increased 17-fold in each of the two epinephrine groups. During the epinephrine infusion, gluconeogenesis accounted for a maximum of 55% of total glucose production as opposed to 31% during insulin deficiency alone. An increase in cortisol alone during insulin deficiency (SAL+CORT) had no effect on glucose level, glucose production, or gluconeogenesis. These results suggest that small increases in the plasma epinephrine level during insulin deficiency can significantly worsen the resulting hyperglycemia through stimulation of both glycogenolysis and gluconeogenesis.(ABSTRACT TRUNCATED AT 400 WORDS)

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