Central insulin and macronutrient intake in the rat.
Chavez, Mark, Christine A. Riedy, Gertjan Van Dijk, and Stephen C.
Woods.
Departments of Psychology, and Medicine, and Department of Animal
Physiology, University of Washington, Seattle WA, 98195, and
University of Groningen, P.O. Box 14, 9750 AA Haren, The
Netherlands
APStracts 3:0133R, 1996.
When rats are maintained on a standard laboratory diet, the infusion
of low doses of insulin into the cerebroventricular system causes a
reduction of food intake and body weight. It was recently reported
that if rats are maintained on a high-fat diet (56% calories as fat),
they are insensitive to this action of insulin. To investigate
further the effect of dietary composition on responsiveness to
central insulin, we carried out two experiments. In Experiment 1,
rats were maintained on one of four equicaloric diets (providing 7%,
22%, 39% or 54% of calories as fat) before and during a 6-day third
-ventricular infusion (i3vt) of insulin (10 mU/day) or saline. Rats
consuming 7% or 22% of calories as fat had a significant reduction of
both food intake (-17.2 +/- 2.9 and -14.6 +/- 3.3 g, respectively)
and body weight (-50 +/- 5 and -41 +/- 5 g, respectively) from
baseline over the insulin-infusion period. Rats consuming 39% or 54%
calories as fat did not reliably alter food intake (-4.0 +/- 3.9 and
-1.9 +/- 3.7 g, respectively) or body weight (-10 +/- 6 and -6 +/- 4
g, respectively) in response to i3vt of insulin. In Experiment 2,
rats were offered a choice of three macronutrients (carbohydrates,
fats and proteins) in separate jars in their home cages. After they
had adapted to the diets, they were infused i3vt with insulin or
saline. Insulin caused a significant reduction of body weight
relative to saline-infused controls (body weight: -23.+/- 4 g), and a
reduction in food intake which was selective for dietary fat. These
data suggest that the effects of central insulin administration are
highly dependent upon the macronutrient content of the diet as well
as the ability of rats to select their own diets.
Received 19 September 1995; accepted in final form 18 March 1996.
APS Manuscript Number R583-5.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 16 April 96