Pregastric food-contingent stimulation elicits drinking in the absence of systemic dehydration in the rat

Adult male Sprague-Dawley rats surgically fitted with a stainless steel gastric cannula were prepared following 24-h food deprivation for sham feeding liquid diet with open gastric fistula. Sham feeding (pregastric food-contingent stimulation) of 5, 10, 20 or 40 ml of liquid diet elicited water intake that was not in proportion to volume of liquid diet sham fed. Rats sham feeding between 1 and 68 ml of sweetened milk showed no evidence of cellular or extracellular dehydration as measured by plasma osmolality and hematocrit, respectively. Subcutaneous injection of 100 mg/kg captopril, a dose sufficient to block conversion of angiotensin I to angiotensin II in brain and periphery, inhibited drinking elicited by sham feeding without effect on sham feeding. These results demonstrate that pregastric food-contingent stimulation elicits water intake that is not in proportion to amount of liquid diet sham fed and that occurs in the apparent absence of systemic dehydration. That such drinking could depend upon endogenous angiotensin II provokes consideration of a role for angiotensin II in the mediation of a pregastric (perhaps histaminergic) mechanism that initiates drinking in advance of postprandial dehydration.