INSULIN RESPONSES TO A FAT MEAL IN HYPOTHALAMIC MICRODIALYSATES AND PLASMA

In a recent microdialysis study in freely-behaving rats, we observed c hanges in immunoreactive insulin (IRI) in hypothalamic dialysates afte r a meal of standard laboratory chow. These changes did not always par allel plasma insulin variations, suggesting a partial independence fro m peripheral insulin. In the present study, we have attempted to asses s the profile of medial hypothalamus (VMH-PVN) extracellular insulin a nd peripheral insulin before and after a fat meal (lard). In contrast to the increase we previously observed with chow meals, hypothalamic e xtracellular IRI decreased during the fat meal and fell to 60% 30 min after the meal. plasma insulin levels did not change. The intake of th e lard meal, provided in unlimited amounts, was much larger in calorie s than the intake of a chow meal under the same conditions. However, w hen rats were offered a meal of chow after they had eaten a meal avera ging 6.7 g of fat (61 calories), they immediately began eating the cho w. Thus, the meal of fat produced no general satiation. On the contrar y, the rats consumed a second chow meal only after a delay of approxim ately 40 min after the first one. The present data, in conjunction wit h our previous observations with chow fed rats, suggest that the level of extracellular hypothalamic IRI may decrease independently of plasm a insulin levels and may, at least partially, account for the observed lack of satiation. (C) 1997 Elsevier Science Inc.