ACUTE BLOOD-VOLUME EXPANSION DELAYS THE GASTROINTESTINAL TRANSIT OF ACHARCOAL MEAL IN AWAKE RATS

The present study evaluates the effect of blood volume expansion on th e gastrointestinal transit of a charchoal meal(2.5 mi of an aqueous su spension consisting of 5% charcoal and 5% gum arabic) in awake male Wi star rats (200-270 g). On the day before the experiments, the rats wer e anesthetized with ether, submitted to left jugular vein cannulation and fasted with water ad libitum until 2 h before the gastrointestinal transit measurement. Blood volume expansion by iv infusion of 1 ml/mi n Ringer bicarbonate in volumes of 3, 4 or 5% body weight delayed gast rointestinal transit at 10 min after test meal administration by 21.3- 26.7% (P<0.05), but no effect was observed after 1 or 2% body weight e xpansion. The effect of blood volume expansion (up to 5% body weight) on gastrointestinal transit lasted for at least 60 min (P<0.05). Mean arterial pressure increased transiently and central venous pressure in creased and hematocrit decreased (P<0.05). Subdiaphragmatic vagotomy a nd yohimbine (3 mg/kg) prevented the delay caused by expansion on gast rointestinal transit, while atropine (0.5 mg/kg), L-NAME (2 mg/kg), he xamethonium(10 mg/kg), prazosin (1 mg/kg) or propranolol (2 mg/kg) wer e ineffective. These data show that blood volume expansion delays the gastrointestinal transit of a charcoal meal and that vagal and yohimbi ne-sensitive pathways appear to be involved in this phenomenon. The de lay in gastrointestinal transit observed here, taken together with the modifications of gastrointestinal permeability to salt and water repo rted by others, may be part of the mechanisms involved in liquid exces s management.