Central exendin-4 infusion reduces body weight without altering plasma leptin in (fa/fa) Zucker rats.

OBJECTIVE: To investigate whether chronic administration of the long-acting glucagon-like peptide-1 receptor agonist exendin-4 can elicit sustained reductions in food intake and body weight and whether its actions require an intact leptin system. RESEARCH METHODS AND PROCEDURES: Male lean and obese Zucker (fa/fa) rats were infused intracerebroventricularly with exendin-4 using osmotic minipumps for 8 days.
RESULTS: Exendin-4 reduced body weight in both lean and obese Zucker rats, maximum suppression being reached on Day 5 in obese (8%) and Day 7 in lean (16%) rats. However, epididymal white adipose tissue weight was not reduced, and only in lean rats was there a reduction in plasma leptin concentration. Food intake was maximally suppressed (by 81%) on Day 3 in obese rats but was reduced by only 18% on Day 8. Similarly, in lean rats food intake was maximally reduced (by 93%) on Day 4 of treatment and by 45% on Day 8. Brown adipose tissue temperature was reduced from Days 2 to 4. Plasma corticosterone was elevated by 76% in lean but by only 28% in obese rats. DISCUSSION: Chronic exendin-4 treatment reduced body weight in both obese and lean Zucker rats by reducing food intake: metabolic rate was apparently suppressed. These effects did not require an intact leptin system. Neither does the absence of an intact leptin system sensitize animals to exendin-4. Partial tolerance to the anorectic effect of exendin-4 in lean rats may have been due to elevated plasma corticosterone and depressed plasma leptin levels, but other counter-regulatory mechanisms seem to play a role in obese Zucker rats.