CHRONIC ADMINISTRATION OF OB PROTEIN DECREASES FOOD-INTAKE BY SELECTIVELY REDUCING MEAL SIZE IN FEMALE RATS

The mechanisms by which OB protein controls food intake and energy bal ance are unknown. Therefore, we investigated the effects of a novel mo dified human recombinant OB protein (Mod-OB) on spontaneous feeding pa tterns, body weight, running wheel activity, and ovarian cycling in fe male rats. Mod-OB or vehicle was injected (4 mg . kg(-1) . day(-1) sc) for 2 ovarian cycles (8 days) using a within-subjects design. Observa tions were continued for five ovarian cycles after injections; treatme nts were then reversed. Mod-OB reduced food intake similar to 20% from injection day I to postinjection day 2. Body weight was reduced from injection day 3 to postinjection day 15 (maximum decrease, 25 +/- 4 g, postinjection days 3 and 4). Food intake was reduced due to decreases in nocturnal meal size, which appeared to be superimposed on the norm al pattern of spontaneous feeding (i.e., reductions in meal size at es trus). Mod-OB did not significantly affect diurnal food intake or meal patterns, failed to alter wheel running, and did not disrupt the rats ' ovarian cycles. We conclude that chronically administered Mod-OB red uces food intake in female rats by selectively affecting the mechanism s controlling meal size.