Portal glucose infusion increases hepatic glycogen deposition in consciousunrestrained rats

It has been demonstrated in the conscious dog that portal glucose infusion creates a signal that increases net hepatic glucose uptake and hepatic glyc ogen deposition. Experiments leading to an understanding of the mechanism b y which this change occurs will be facilitated if this finding can be repro duced in the rat. Rats weighing 275-300 g were implanted with four indwelli ng catheters (one in the portal vein, one in the left carotid artery, and t wo in the light jugular vein) that were externalized between the scapulae. The rats were studied in a conscious, unrestained condition 7 days after su rgery, following a 24-h fast. Each experiment consisted of a 30- to 60-min equilibration, a 30-min baseline, and a 120-min test period. In the test pe riod, a pancreatic clamp was performed by using somatostatin, insulin, and glucagon. Glucose was given simultaneously either through the jugular vein to clamp the arterial blood level at 220 mg/dl (Pe low group) or at 250 mg/ dl (Pe high group), or via the hepatic portal vein (Po group; 6 mp.kg(-1).m in(-1)) and the jugular vein to clamp the arterial blood glucose level to 2 20 mg/dl. In the test period, the arterial plasma glucagon and insulin leve ls were not significantly different in the three groups (36 +/- 2, 33 +/- 2 , and 30 +/- 2 pg/ml and 1.34 +/- 0.08, 1.37 +/- 0.18, and 1.66 +/- 0.11 ng /ml in Po, Pe low; and Pe high groups, respectively). The arterial blood gl ucose levels during the test period were 224 +/- 4 mg/dl for Po, 220 +/- 3 for Pe low and 255 +/- 2 for Pe high group. The Liver glycogen content (mu mol glucose/g liver) in the two Pe groups was not statistically different ( 51 +/- 7 and 65 +/- 8, respectively), whereas the glycogen level in the Po group was significantly greater (93 +/- 9, P < 0.05). Because portal glucos e delivery also augments hepatic glycogen deposition in the rat, as it does in the dogs, mechanistic studies relating to its function can now be under taken in this species.