VARIATIONS IN GASTRIC-EMPTYING OF LIQUID ELICITED BY ACUTE BLOOD-VOLUME CHANGES IN AWAKE RATS

We have observed that acute blood volume expansion increases the gastr oduodenal resistance to the flow of liquid in anesthetized dogs, while retraction decreases it (Santos et al. (1991) Acta Physiologica Scand inavica, 143: 261-269). This study evaluates the effect of blood volum e expansion and retraction on the gastric emptying of liquid in awake rats using a modification of the technique of Scarpignato (1980) (Arch ives Internationales de Pharmacodynamie et de Therapie, 246: 286-294). Male Wistar rats (180-200 g) were fasted for 16 h with water ad libit um and 1.5 ml of the test meal (0.5 mg/ml phenol red solution in 5% gl ucose) was delivered to the stomach immediately after random submissio n to one of the following protocols: 1) normo-volemic control (N = 22) , 2) expansion (N = 72) by intravenous infusion (1 ml/min) of Ringer-b icarbonate solution, volumes of 1, 2, 3 or 5% body weight, or 3) retra ction (N = 22) by controlled bleeding (1.5 mV/100 g). Gastric emptying of liquid was inhibited by 19-51.2% (P<0.05) after blood volume expan sion (volumes of 1, 2, 3 or 5% body weight). Blood volume expansion pr oduced a sustained increase in central venous pressure while mean arte rial pressure was transiently increased during expansion (P<0.05). Blo od volume retraction increased gastric emptying by 28.5-49.9% (P<0.05) and decreased central venous pressure and mean arterial pressure (P<0 .05). Infusion of the shed blood 10 min after bleeding reversed the ef fect of retraction on gastric emptying. These findings suggest that ga stric emptying of liquid is subject to modulation by the blood volume.