EFFECTS OF 2 WEEKS OF FEED RESTRICTION ON SOME COMMON TOXICOLOGIC PARAMETERS IN SPRAGUE-DAWLEY RATS

This study was intended to identify changes caused by short-term reduc ed feed intake in rats such as may occur with unpalatable feed or othe r forms of anorexia. For 2 wk, groups of rats (10/sex/group) were fed ad libitum (control group) or given 75% (mildly restricted group), 50% (moderately restricted group), or 25% (severely restricted group) of the amount of feed eaten the day before by controls. The control group and mildly restricted group grew steadily, but the terminal body weig hts of the mildly restricted group (both males and females) were only about 80% of controls. The moderately restricted group did not grow du ring the first week but grew slightly during the second week (terminal body weights about 65% of control). The severely restricted group los t weight throughout the study (terminal weight about 40% of control). Restricted groups exhibited hemoconcentration directly related to the degree of feed restriction. White blood cell counts were reduced (prin cipally due to lymphopenia) in severely restricted rats. Platelet coun ts were decreased in all restricted groups. Total serum protein concen tration was reduced (decreased globulins) in all female restricted gro ups and in the severely restricted males. The severely restricted rats had increased serum bilirubin, electrolyte derangements, and (in fema les only) decreased cholesterol. Thymus and liver weights (absolute an d relative) were decreased in the moderately and severely restricted g roups. All the feed-restricted groups had an increased incidence of su perficial gastric erosions. The mildly and moderately restricted group s had slightly decreased hematopoietic tissue in sternal bone marrow, while the severely restricted group had bone marrow necrosis, thymic a trophy, and mild testicular degeneration. Findings in the severely res tricted group were distinct from those in the other groups on the basi s of their severity and were considered adverse. Changes in the mildly and moderately restricted groups were considered adaptive and innocuo us since feed restriction of this degree has historically been associa ted with increased longevity and decreased disease incidence in chroni c studies.