Closing the pylorus decreases the size of large meals in the rat

We previously reported (Davis, J. D.; Smith G. P.; Sayler, J. L. Reduction of intake in the rat due to gastric filling. Am. J. Physiol. 272:R1599-R1605, 1997.) that confining ingested fluid to the stomach by closing the pylorus decreased the intake of solutions that stimulated particularly large intakes. Those solutions differed in the type of orosensory and postoral stimulation so the nature of the control over ingestion was unclear. We report here a study of the role of orosensory stimulation alone in controlling intake in rats with a closed pylorus. Rats were given 30-min intake tests with the pylorus open and closed with 0.2 M glucose, and with 0.2 M glucose + 1.25 mM sodium saccharin, 2.5 mM sodium saccharin and 5.0 mM sodium saccharin. Intake was reduced on the cuff-closed test relative to the cuff-open test with the two highest concentrations of saccharin, but not with the two lowest. When ingesting the glucose solutions with the two highest concentrations of saccharin the initial rate of ingestion was greater and the decline in the rate of ingestion was slower than when the rats ingested the glucose solutions with 1.25 mM saccharin or no saccharin. We showed by means of a meta-analysis of previously published and unpublished data that a high rate of licking at the beginning of a test combined with a relatively slow rate of decline in the rate of licking during it are the characteristics of ingestive behavior on cuff-open tests that will lead to a reduction of intake when ingested fluid is confined to the stomach.