Temporal changes in meal number and meal size in response to rHu IL-1alpha.

Peripherally infused interleukin-1 reduces food intake. Its temporal and selective effects on meal number and meal size were investigated in seven rats continuously infused for 3 days with recombinant human interleukin-1 alpha (rHu IL-1 alpha; 3 micrograms day-1, i.v.). Food intake decreased significantly during the first two infusion days, and was brought about by first the early reduction of meal number, followed by meal size with a 1 day delay. The primary effect of rHu IL-1 alpha was seen during the dark cycle. After the infusion was stopped, meal number recovered most quickly, followed by a lag in recovery of meal size. We conclude that rHu IL-1 alpha influenced food intake primarily via an effect on meal number, which responds more rapidly than a decrease in meal size, thereby inducing an immediate decrease in food intake.