The effect of chronic underfeeding on organ weights of rats. How to interpret organ weight changes in cases of marked growth retardation in toxicity tests?

Growing male rats were kept on a restricted feed intake. After 13 weeks they reached a final body weight of 250 g in comparison with 366 g of their ad lib. fed controls. The relative weights of the heart, kidneys, spleen, pituitary and prostate/seminal vesicle were not altered by underfeeding. The relative weights of the brain, adrenals and tests were increased by 30 to 40% in the feed-restricted groups, the thyroid by about 20%. The relative weight of the liver was decreased by about 30%. When growth is markedly reduced in a toxicity experiment alterations of this kind in the organ weight: body weight ratios have to be expected as a physiological response of the organism to decreased feed intake. They must be differentiated from organ weight changes resulting from primary toxic influences of the drug tested.