RESUMEN
We previously reported that infection decreases hepatic glucose uptake when glucose is given as a constant peripheral glucose infusion (8 mg. kg(-1) x min(-1)). This impairment persisted despite greater hyperinsulinemia in the infected group. In a normal setting, hepatic glucose uptake can be further enhanced if glucose is given gastrointestinally. Thus the aim of this study was to determine whether hepatic glucose uptake is impaired during an infection when glucose is given gastrointestinally. Thirty-six hours before study, a sham (SH, n = 7) or Escherichia coli-containing (2 x 10(9) organisms/kg; INF; n = 7) fibrin clot was placed in the peritoneal cavity of chronically catheterized dogs. After the 36 h, a glucose bolus (150 mg/kg) followed by a continuous infusion (8 mg. kg(-1). min(-1)) of glucose was given intraduodenally to conscious dogs for 240 min. Tracer ([3-(3)H]glucose and [U-(14)C]glucose) and arterial-venous difference techniques were used to assess hepatic and intestinal glucose metabolism. Infection increased hepatic blood flow (35 +/- 5 vs. 47+/-3 ml x g(-1) x min(-1); SH vs. INF) and basal glucose rate of appearance (2.1+/-0.2 vs. 3.3+/-0.1 mg x kg(-1) x min(-1)). Arterial insulin concentrations increased similarly in SH and INF during the last hour of glucose infusion (38+/-8 vs. 46+/-20 microU/ml), and arterial glucagon concentrations fell (62+/-14 to 30+/-3 vs. 624+/-191 to 208+/-97 pg/ml). Net intestinal glucose absorption was decreased in INF, attenuating the increase in blood glucose caused by the glucose load. Despite this, net hepatic glucose uptake (1.6+/-0.8 vs. 2.4+/- 0.9 mg x kg(-1) x min(-1); SH vs. INF) and consequently tracer-determined glycogen synthesis (1.3+/-0.3 vs. 1.0+/-0.3 mg. kg(-1) x min(-1)) were similar between groups. In summary, infection impairs net glucose absorption, but not net hepatic glucose uptake or glycogen deposition, when glucose is given intraduodenally.
Asunto(s)
Infecciones por Escherichia coli/metabolismo , Glucosa/administración & dosificación , Glucosa/farmacocinética , Hígado/metabolismo , Animales , Glucemia/análisis , Perros , Duodeno , Infecciones por Escherichia coli/fisiopatología , Femenino , Glucagón/sangre , Glucosa/farmacología , Hemodinámica , Inyecciones , Insulina/sangre , Absorción Intestinal , Mucosa Intestinal/metabolismo , Cinética , Circulación Hepática/efectos de los fármacos , Hormonas Pancreáticas/metabolismoRESUMEN
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.