The effects of chronic administration of naltrexone on appetite and water exchange in rats.

The effects of chronic administration of naltrexone (200 microgram/kg/hr) on appetitive behaviors and renal water and electrolyte excretions were studied in rats. Naltrexone reduced food and water intake, the renal excretions of water and electrolyte excretions were studied in rats. Naltrexone reduced food and water intake, the renal excretions of water and electrolytes, and osmolar clearance. No changes in plasma levels of electrolytes, plasma and urine Na+-K+ ratios, hematocrit ratio, plasma osmolality, the clearances of K+ and Na+, and the reabsorption of solute free water were found. The changes in appetite were compensated for by appropriate changes in renal excretions, resulting in no change in electrolyte balance or water exchange. These observations are discussed in relation to current theories of the role of endorphins in appetite control.