Effect of morphine on caloric intake and macronutrient selection in male and female Lou/c/jall rats during ageing

Previous studies have showed a shift of preferences from carbohydrate to fa t in the Lou/c/jall rat with advancing age when they are submitted to a sel f-selection procedure. Protein intake also decreased according to the age, earlier for males (after 16 months) than for females (29 months). The prese nt study aimed at investigating the mechanism underlying these modification s. We analysed the effect of the reference mu agonist, morphine (5 mg/kg su bcutaneous), on the caloric intake, body weight and macronutrient intake of 30 male and 30 female rats divided in four age groups: young adults (10), mature (17), old (24) and senescent rats (29 months). During the experiment , animals had the choice between separate sources of the three pure macronu trients. Morphine injection reduced total daily caloric intake and induced a decrease in body weight. The weight loss was age- and sex-related (males and old rats were more affected by the drugs). The injection of morphine ev oked a triphasic influence on the chronology of the intake. A brief (1 h) h ypophagia was followed by an hyperphagia, (3 h) and a persistent hypophagia (8 h). No modification in the diet composition was observed. These results did not support a clear involvement of the opioid system concerning the mo difications in macronutrient rates in diet previously observed across agein g. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.