Metabolic Fate of the Glucose Taken up by the Intestine During Induced Hyperglycaemia in Dogs

S T Shittu, AR A Alada, DD O Oyebola

Abstract


Available data showed that the intestine increases it glucose uptake in response to hyperglycemia induced by any
cause. However, what the intestine does with the glucose is not known. This study investigated the metabolic fate of the
glucose taken up by the intestine during hyperglycaemia in dogs. Experiments were carried out on fasted, male, anaesthetized
mongrel dogs divided into 4 groups. The control (group 1, n=5) received normal saline (0.2 ml/kg) while groups 2-4
(subdivided into two as low or high dose, n=5 each) received adrenaline (1 μg/kg or 5 μg/kg), glucagon (3 ng/kg or 8 ng/kg)
and glucose (10 mg/kg/min or 20 mg/kg/min). Through a midline laparatomy, the upper jejunum was cannulated for Intestinal
Blood Flow (IBF) measurement. Blood glucose and lactate levels were determined using glucose oxidase and lactate
dehydrogenase methods, respectively. Intestinal Glucose/Lactate Uptake (IGU/ILU) was calculated as the product of IBF
and arterio-venous glucose /lactate difference [(A-V) glucose/lactate]. Jejunal tissue samples were obtained for the determination
of Glycogen Content (GC) and activities of Glycogen Synthase (GS), Glycogen Phosphorylase ‘a’ (GPa), hexokinase and
glucose-6-phosphatase. Anthrone method was used to determine GC while activities of GS, GPa, hexokinase and glucose-
6-phosphatase were determined spectrophotometrically. Data were subjected to descriptive statistics and analyzed using
student’s t-test and ANOVA at α0.05. Arterial and venous blood glucose and lactate were increased by adrenaline, glucagon
and glucose. Venous lactate was higher than arterial lactate in all groups. Intestinal blood flow, (A-V) glucose and (A-V)
lactate were increased in all the experimental groups. Intestinal glucose uptake increased by 624% (adrenaline), 705%
(glucagon) and 589% (glucose) while intestinal lactate release increased by 422%, 459% and 272% respectively. Intestinal
GC increased from 138.72 ± 4.58 mg/100 g to 167.17 ± 4.20 mg/100 g (adrenaline), 229.21 ± 6.25 mg/100 g (glucagon) and
165.17 ± 4.20 mg/100 g (glucose). Adrenaline and glucose had no effect on GS activity but it was increased by glucagon;
GPa was decreased while hexokinase activity was increased by adrenaline, glucagon, and glucose. Glucose-6-phosphatase
activity was not affected by adrenaline and glucagon but decreased by glucose. The intestine modulates blood glucose levels
through lactate formation, glycogen formation and most probably conversion of lactate to glucose through gluconeogenesis.

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