Long-term feeding of casein or soy protein with or without cholesterol in Mongolian gerbils. I. Morphologic effects

This study was designed to determine whether male Mongolian gerbils (Meriones unguiculatus) develop atherosclerosis (AS) during long-term feeding of diets similar to those consumed by humans. Gerbils were fed diets containing 16% casein (C) or soy (S) protein +/- 0.1% cholesterol (CH) for 15 months. The energy contribution from protein, fat and carbohydrate was similar to the energy distribution reported for the average North American (NA) diet and the level of added dietary CH resembled the average NA intake. At mo 0, 3, 6, 9, 12 and 15, animals were killed and tissue sections were prepared for histologic examination. Microscopic observations of cardiovascular tissues did not reveal any evidence of AS in any of the diet groups. Liver fatty infiltration (FI) was evident in the C+CH and C groups at mo 3 and 9, respectively, and continued to occur at all subsequent sampling times. Livers from gerbils fed S+CH also began to exhibit FI at mo 9, while livers from S-fed gerbils did not show any significant morphologic changes. Biochemical liver total lipid results supported the histological liver findings. Other tissues examined did not reveal any morphological changes related to diet. The gerbil may be a useful animal model to study mechanisms which inhibit AS development.