Independence of the effects of d-amphetamine and food deprivation or body weight on the food consumption of rats

Two experiments studied the combined effects of absolute doses (milligrams per rat) of d-amphetamine with either food deprivation (Experiment I) or body weight (Experiment II) on the food consumption of rats. In the first experiment, each of 16 rats was tested once under every combination of three levels of food deprivation (0, 12, and 24 h) and three levels of drug (0, 0.33, and 1.0 mg per rat). Food consumption was measured over 2.5-h sessions that began 30 min after injection. Increasing doses of d-amphetamine and decreasing levels of food deprivation both decreased food consumption, but the effects of the two variables were additive with nonsignificant interaction.In the second experiment, four groups of four rats each, differing in age and body weight, were studied. Under 48-h food deprivation, each rat received each of four doses of d-amphetamine (0, 0.27, 0.54, and 0.81 mg). Food consumption was measured over a 2.5-h period that began 30 min after injection. Increasing doses of d-amphetamine and decreased body weights decreased food consumption, and the combined effects of these two variables were additive. The lack of an interaction between dose and differing body weights in these experiments indicates that the generally-accepted mode of administering d-amphetamine, as milligrams per kilograms of body weight, does not equate rats of differing body weights.This reserch was supported by USPHS reserch grant MH-01604 from the National Institutes of Mental Health. We thank Smith, Kline and French Laboratory for supplying the d-amphetamine used in this study. Robert C. MacPhail is now at the Department of Pharmacology, The University of Chicago, Chicago, Illinois 60637.