Pressures were measured with miniature transducers positioned within t
he gastric lumen of six young pigs, 20-40 kg, eating and drinking oper
antly. The pigs were free to move about, lie down, sleep, eat, and dri
nk without disturbance. 1) At the end of 4-5-h fasts (with no drinking
), mean pressure within the stomach was 12 cm H2O, then rose during 22
-min eating bouts to 22 cm H2O. 2) At the end of 16-18-h periods of fo
od and water deprivation, intragastric pressure was 9 cm H2O. When wat
er was drunk, pressures rose only to 13 cm H2O, then fell. When food w
as then eaten, pressures rose during 29-min meals to 22 cm H2O. 3) Dur
ing spontaneous eating and drinking, intermeal pressures were maintain
ed at 22-25 cm H2O, fell by 4-5 cm H2O just as eating or drinking bega
n, then rose slowly, but only to the preingestive pressure level by th
e end of the bout. These results indicate that during spontaneous eati
ng and drinking, gastric distention per se plays a smaller direct role
in causing satiety than it does during meals ingested after a period
of food deprivation.