Joseph Ejiofor

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 μg·kg−1·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·kgα−1·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.

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.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-1before 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.

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.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 μU/ml). In addition, the majority (79 ± 13%) of the glucose taken up by the liver was released as lactate (34 ± 6 μmol ⋅ 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 μmol ⋅ 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 μU/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.

Regulation of glucose production by NEFA and gluconeogenic precursors during chronic glucagon infusion.

We previously reported that simulation of the chronic hyperglucagonemia seen during infection was unable to recreate the infection-induced increase in hepatic glucose production. However, chronic hyperglucagonemia was accompanied by a fall in the arterial levels of gluconeogenic precursors as opposed to a rise as is seen during infection. Thus our aim was to determine whether an infusion of gluconeogenic precursors could increase hepatic glucose production in a setting of hyperglucagonemia. Studies were done in 11 conscious chronically catheterized dogs in which sampling (artery and portal and hepatic veins) and infusion catheters (splenic vein) were implanted 17 days before study. Forty-eight hours before infusion of gluconeogenic (GNG) precursors, a sterile fibrinogen clot was placed into the peritoneal cavity. Glucagon was infused over the subsequent 48-h period to simulate the increased glucagon levels (∼500 pg/ml) seen during infection. On the day of the experiment, somatostatin was infused peripherally, and basal insulin and simulated glucagon were infused intraportally. After a basal period, a two-step increase in lactate and alanine was initiated (120 min/step; n= 5). Lactate (Δ479 ± 25 and Δ1,780 ± 85 μM; expressed as change from basal in periods I and II, respectively) and alanine (Δ94 ± 13 and Δ287 ± 44 μM) levels were increased. Despite increases in net hepatic GNG precursor uptake (Δ0.7 ± 0.3 and Δ1.1 ± 0.4 mg glucose ⋅ kg-1 ⋅ min-1), net hepatic glucose output did not increase. Because nonesterified fatty acid (NEFA) levels fell, in a second series of studies, the fall in NEFA was eliminated. Intralipid and heparin were infused during the two-step substrate infusion to maintain the NEFA levels constant in period I and increase NEFA availability in period II (Δ -29 ± 29 and Δ689 ± 186 μM; n = 6). In the presence of similar increases in net hepatic GNG precursor uptake and despite increases in arterial glucose levels (Δ17 ± 5 and Δ38 ± 12 mg/dl), net hepatic glucose output increased (Δ0.6 ± 0.1 and Δ0.7 ± 0.2 mg ⋅ kg-1 ⋅ min-1). In summary, a chronic increase in glucagon, when combined with an acute increase in gluconeogenic precursor and maintenance of NEFA supply, increases hepatic glucose output as is seen during infection.We previously reported that simulation of the chronic hyperglucagonemia seen during infection was unable to recreate the infection-induced increase in hepatic glucose production. However, chronic hyperglucagonemia was accompanied by a fall in the arterial levels of gluconeogenic precursors as opposed to a rise as is seen during infection. Thus our aim was to determine whether an infusion of gluconeogenic precursors could increase hepatic glucose production in a setting of hyperglucagonemia. Studies were done in 11 conscious chronically catheterized dogs in which sampling (artery and portal and hepatic veins) and infusion catheters (splenic vein) were implanted 17 days before study. Forty-eight hours before infusion of gluconeogenic (GNG) precursors, a sterile fibrinogen clot was placed into the peritoneal cavity. Glucagon was infused over the subsequent 48-h period to simulate the increased glucagon levels (approximately 500 pg/ml) seen during infection. On the day of the experiment, somatostatin was infused peripherally, and basal insulin and simulated glucagon were infused intraportally. After a basal period, a two-step increase in lactate and alanine was initiated (120 min/step; n = 5). Lactate (Delta479 +/- 25 and Delta1, 780 +/- 85 microM; expressed as change from basal in periods I and II, respectively) and alanine (Delta94 +/- 13 and Delta287 +/- 44 microM) levels were increased. Despite increases in net hepatic GNG precursor uptake (Delta0.7 +/- 0.3 and Delta1.1 +/- 0.4 mg glucose . kg-1 . min-1), net hepatic glucose output did not increase. Because nonesterified fatty acid (NEFA) levels fell, in a second series of studies, the fall in NEFA was eliminated. Intralipid and heparin were infused during the two-step substrate infusion to maintain the NEFA levels constant in period I and increase NEFA availability in period II (Delta -29 +/- 29 and Delta689 +/- 186 microM; n = 6). In the presence of similar increases in net hepatic GNG precursor uptake and despite increases in arterial glucose levels (Delta17 +/- 5 and Delta38 +/- 12 mg/dl), net hepatic glucose output increased (Delta0.6 +/- 0.1 and Delta0.7 +/- 0.2 mg . kg-1 . min-1). In summary, a chronic increase in glucagon, when combined with an acute increase in gluconeogenic precursor and maintenance of NEFA supply, increases hepatic glucose output as is seen during infection.

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 iu,g/kg/effects of a 4 h intraportal infusion of Escherichia coli lipopolysaccharide (LPS, .21 iu,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-a EIA kit (ELISA; Biosource, Camarillo, CA). Using WEHI, arterial TNF levels increased from 10 ±6 pg/mL to a peak of 4667 ±1442 pg/mL -100 min after LPS and fell to 443 ±199 pg/mL by 240 min. Using ELISA, arterial TNF levels increased from 5 ±5 pg/mL to a peak of 12,234 ±2046 pg/mLat~ 100 min and fell to 3511 & plusmn;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±10.7 ng/kg/min at 60 min and returned toward basal by 240 min (4.7 ±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. 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-a EIA kit (ELISA; Biosource, Camarillo, CA). Using WEHI, arterial TNF levels increased from 10 ±6 pg/mL to a peak of 4667 ±1442 pg/mL -100 min after LPS and fell to 443 ±119pg/mL by 240 min. Using ELISA, arterial TNF levels increased from 5 ±5 pg/mL to a peak of 12,234 ±2046 pg/mLat~ 100 min and fell to 3511±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 ±10.7 ng/kg/min at 60 min and returned toward basal by 240 min (4.7 ±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 majojgrity 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.