The effect of fasting time on plasma total cholesterol concentration in Mongolian gerbils.

This study investigated the effect of length of fasting time on plasma total cholesterol response of male Mongolian gerbils (Meriones unguiculatus). Plasma cholesterol levels from fed and fasted gerbils were also compared with those reported for humans under similar metabolic states. Plasma total cholesterol response showed a significant quadratic relationship with time over a 15-hour period. Between 6 and 9 hours of fasting (the time during which plasma triglyceride concentration became relatively constant), the average plasma total cholesterol concentration was 178 mg/dl, compared with a zero hour (fed) cholesterol level of 265 mg/dl. The difference in plasma cholesterol levels observed in fed and fasted gerbils is unlike what has been reported for humans. Results from most human studies show no differences in plasma total cholesterol concentrations for fed and fasted subjects. Failure to consider species differences in metabolic responses may have implications when results from animal experiments are extrapolated to humans.

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.

Long-term feeding of casein or soy protein with or without cholesterol in Mongolian gerbils. II. Plasma lipid and liver cholesterol responses.

Male Mongolian gerbils (Meriones unguiculatus) were fed casein or soy protein in the presence and absence of dietary cholesterol for 15 months. Diets resembled the average North American diet in energy contributions from protein, fat and carbohydrate, cholesterol content and fatty acid profile. At month 0, 3, 6, 9, 12 and 15, plasma samples were analyzed for total cholesterol (TC), HDL cholesterol (HDLC) and triglyceride (TG) concentrations. Plasma LDL cholesterol (LDLC) was estimated indirectly. Liver TC was also determined at these time points. Comparisons of protein source and cholesterol level were averaged over the 15 month period. Casein-fed gerbils had significantly higher plasma TC and TG levels and lower HDLC levels (as a percent of TC) compared to soy-fed animals, independent of the presence or absence of dietary cholesterol. LDLC was significantly elevated in casein-fed gerbils only when cholesterol was present in the diet. Elevations in plasma TC levels were reflected by elevations in liver TC. Despite plasma lipid elevations that are consistent with the development of atherosclerosis (AS) and coronary heart disease (CHD) in humans, hyperlipidemic gerbils do not develop AS. Further characterization of gerbil lipid metabolism responses to dietary alterations aimed at the prevention of CHD in humans is necessary to elucidate the mechanism for the gerbil's resistance to AS.