The present study assessed meal-contingent insulin effects on spontane
ous meal patterns. Rats, trained to lever press for daily food require
ments, showed stable meal patterns and were then implanted with hepati
c-portal catheters. Once again stable in ingestion, animals received e
ither physiological saline or vehicle plus 1 or 2 mU of regular, short
-acting insulin beginning at 10 pellets into each initiated meal (whic
h was the chosen minimum meal size definition). All meals during that
day were then infused with the same solution and comparisons were made
within animals (across days) only. Insulin reduced the size of sponta
neous meals at both 1 mU (p < .01) and 2 mU doses (p < .001). No other
meal parameters were significantly affected. In a complementary study
, rats trained to lever press showed increases in meal size when ''rec
overing from'' a diazeoxide-adulterated diet (diazeoxide has been show
n to limit insulin release). Thus, when insulin is increased during sp
ontaneously taken meals, those meals are reduced in size and drugs whi
ch block insulin release, increase the size of meals; we assert insuli
n is a prandial satiety hormone which likely reduced feeding by increa
sing glucose uptake into peripheral tissue.