Postingestive inhibitory controls of independent ingestion in 12-day-old rats.

The postingestive inhibitory control of independent ingestion produced by gastric preloads was investigated in 12-day-old Sprague-Dawley rats. Pups received isovolumetric (5% of body weight) preloads of saline (0.9%), glucose (5%, 10%, or 20%) or maltose (5%, 10%, or 20%) 5 min before a 30-min independent ingestion test in which pups licked milk from the floor of the test chamber. All preloads reduced intake significantly compared to the control condition in which pups were intubated, but no preload was administered. The reduction of intake produced by the isovolumetric, isotonic solutions (saline, 5% glucose, and 10% maltose) is consistent with the stimulation of a preabsorptive, inhibitory mechanism sensitive to volume. The significantly larger reduction of intake produced by isovolumetric, hypertonic solutions (20% glucose and 20% maltose) is consistent with the stimulation of an additional postingestive inhibitory mechanism sensitive to the osmotic, saccharidic, or, in the case of 20% glucose, metabolic properties of these solutions. Because preloads were given 5 min prior to the intake tests, it is likely that the site of action of both inhibitory mechanisms was preabsorptive, although a postabsorptive site for part of the inhibitory effect of 20% glucose cannot be excluded.