INTESTINAL HAEMODYNAMICS AND GLUCOSE UPTAKE FOLLOWING HEXOSES ADMINISTRATION IN DOGS

Abstract

An increase in blood glucose levels has been reported to induce a rise in Intestinal Glucose Uptake (IGU) through reduction in Intestinal Vascular Resistance (IVR) and increase in Intestinal Blood Flow (IBF). However, reports on other hexoses are few and inconclusive. The effects of fructose, galactose and glucose on intestinal haemodynamics and glucose uptake were therefore investigated. The roles of adrenergic receptors and Nitric Oxide (NO) were examined. Experiments were carried out on sixty five fasted male anaesthetized Nigerian local dogs. The control (Group 1, n = 5) received normal saline, while groups 2-4 (n= 5) were infused with glucose (1.1mg/kg/min), fructose (1.1mg/kg/min) and galactose (1.1mg/kg/min), groups 5-7 (n=5), groups 8-10 (n= 5) and groups 11-13 (n= 5) were pretreated with prazosin (0.2mg/kg), propranolol (0.5mg/kg) and L-Nitro-Arginine-Methlyl-Ester (L-NAME) (35mg/kg) respectively followed by infusion with either glucose, fructose or galactose. Through a midline laparatomy, the upper jejunum was secured for IBF measurement by collection of effluent from the cannula placed in the jejunal vein for 60 seconds. Blood samples were obtained for determination of arterial and venous blood glucose. Arterial Blood Pressure (ABP) was measured throughout the experiment using a channel recorder. The IVR was calculated from ABP and IBF; IGU was derived from IBF and Arterio –Venous glucose difference. Blood glucose was determined using the glucose oxidase method. Data were analysed using ANOVA and Student’s t-test at P= 0.05. There were no significant changes in the mean ABP for glucose, fructose, and galactose relative to control (90.45±1.78mmHg). However, following L-NAME pretreatment, ABP for glucose (95.67±1.14mmHg), fructose (101.10±0.68mmHg) and galactose (111.17±1.57mmHg) were higher. The mean IBF in the glucose group (14.40±0.93ml/min) only was significantly higher relative to the control (10.60±0.75ml/min). Arterio–Venous glucose differences were higher in glucose (24.20±2.13mg/dl), fructose (30.83±1.83mg/dl) and galactose (15.20±0.86mg/dl) relative to control (3.40±0.68mg/dl). IGU were higher in glucose (342.20-±40.77mg/dl), fructose (244.40±26.53mg/dl) and galactose (166.60±12.98mg/dl) relative to control (36.80±8.26mg/dl). Following L-NAME pretreatment, there was 50% reduction in the IBF; IVR was higher in glucose (29.87±1.67R.U), fructose (27.90±3.13R.U) and galactose (27.18±1.44R.U) relative to control (9.50±0.80R.U), and 200% reduction in IGU induced by the three sugars. The mean ABP were reduced in Prazosin (76.33±1.74mmHg) and propranolol (81.42±0.67mmHg). There were also reductions in IBF while there was no significant change in IVR following pretreatment with the adrenergic blockers. Propranolol also caused 500% (glucose), 450% (fructose) and 150% (galactose) reductions in IGU while prazosin had no effect on glucose and fructose-induced increases in IGU, but produced 160% reduction in IGU for galactose relative to control. The hyperglycaemia and reduced vascular resistance induced by the three hexoses lead to increase in intestinal glucose uptake.Only glucose increased intestinal blood flow while fructose and galactose had no effect. These effects may be mediated in part by nitric oxide and β adrencoceptors.