Effect of oral versus gastric delivery on gastric emptying of corn oil emulsions

Several studies have shown that fluids delivered to the stomach tend to empty more rapidly than when ingested by mouth. To better characterize the ''delivery route effect'' for corn oil, rats received intragastric or intraoral infusions matched for concentration and for the rate and duration of stimulus delivery. We showed, first, that more than twice as much oil emptied by the end of 12-min intragastric versus intraoral infusions but that the emptying curves remained roughly parallel for 1 h after infusion offset. Remaining experiments therefore focused on stimulus parameters of relevance to emptying control during stomach fill. Emptying during intragastric infusions approximately doubled with doublings of oil concentration (25-50%), infusion duration (6-12 and 12-24 min), and infusion rate (0.5-1.0 ml/min). Emptying during intraoral infusions, by contrast, was entirely unaffected by these manipulations. Unlike oil emptying, glucose emptying did not vary as a function of delivery route. The nutrient specificity of the delivery route effect cannot be explained in terms of energy density, as the effect was obtained for oil but not for glucose when their energy densities were equated (50% glucose, 25% corn oil). In discussion, we suggest that the oral influence on corn oil emptying during stomach fill is a gating factor that enables the expression of inhibition derived from postgastric nutrient stimulation.