The relative contribution of the direct and indirect pathways to liver glycogen formation was assessed in humans by using a combined tracer-hepatic vein catheterization technique. An oral glucose load (75 g) labelled with 1-14C-glucose was administered to five subjects (control group) and 4.5 h later hepatic glycogen was flushed with glucagon and analysed to determine the randomization of 14C. The specific activity (SA) of the glycogen derived glucose (1-14C-glucose SA+recycled 14C-glucose SA) was 61 +/- 7% of the mean blood glucose SA of the interval 0-180 min after the oral glucose load. The relative values due to 1-14C-glucose and recycled 14C-glucose were 33 +/- 7 and 28 +/- 3%, respectively. The data indicate that the indirect pathway of glycogen formation is not only active in humans but contributes substantially (at least 50%) to liver glycogen formation. In order to investigate whether the basal adrenergic tone plays a role in the maintenance of the indirect pathway, the same protocol was also performed in a second group of subjects (n = 5) who received propranolol before the oral glucose load (propranolol group). The SA of the glycogen-derived glucose was considerably smaller than that of the control group (18 +/- 5 vs. 61 +/- 7%, P < 0.001), suggesting lesser glycogen formation. However, the ratio of 1-14C to recycled-14C in the glucose molecule was similar in the control (1.3 +/- 0.4) and propranolol group (1.9 +/- 1.2). We conclude that the basal adrenergic tone does not play any role in the operation of the indirect pathway of liver glycogen synthesis.

Indirect pathway of liver glycogen synthesis in humans is predominant and independent of beta-adrenergic mechanisms

Picardi A;
1992-01-01

Abstract

The relative contribution of the direct and indirect pathways to liver glycogen formation was assessed in humans by using a combined tracer-hepatic vein catheterization technique. An oral glucose load (75 g) labelled with 1-14C-glucose was administered to five subjects (control group) and 4.5 h later hepatic glycogen was flushed with glucagon and analysed to determine the randomization of 14C. The specific activity (SA) of the glycogen derived glucose (1-14C-glucose SA+recycled 14C-glucose SA) was 61 +/- 7% of the mean blood glucose SA of the interval 0-180 min after the oral glucose load. The relative values due to 1-14C-glucose and recycled 14C-glucose were 33 +/- 7 and 28 +/- 3%, respectively. The data indicate that the indirect pathway of glycogen formation is not only active in humans but contributes substantially (at least 50%) to liver glycogen formation. In order to investigate whether the basal adrenergic tone plays a role in the maintenance of the indirect pathway, the same protocol was also performed in a second group of subjects (n = 5) who received propranolol before the oral glucose load (propranolol group). The SA of the glycogen-derived glucose was considerably smaller than that of the control group (18 +/- 5 vs. 61 +/- 7%, P < 0.001), suggesting lesser glycogen formation. However, the ratio of 1-14C to recycled-14C in the glucose molecule was similar in the control (1.3 +/- 0.4) and propranolol group (1.9 +/- 1.2). We conclude that the basal adrenergic tone does not play any role in the operation of the indirect pathway of liver glycogen synthesis.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/20.500.12610/2201
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