Oxygen consumption and thyroid hormones in germfree mice fed glucose-amino acid liquid diet

Germfree rats and mice fed solid diets have previously been shown to consume less oxygen than their conventional counterparts. Young adult germfree C3H/He mice how serum T3 concentrations comparable to those of conventional mice, but their serum T4 values are 10-15% lower. Fed chemically defined liquid glucose-amino acid diets, germfree C3H mice use 27% more oxygen than comparable germfree mice fed a solid natural ingredient diet, and 12% more than conventional mice fed the solid diet. Like germfree rats, the germfree mice fed natural ingredient diet had smaller hearts and livers than those of conventional mice. However, the chemically defined diet-fed germfree C3H mice showed larger hearts than conventional C3H mice fed solid diets, and livers of comparable size. Serum T3 levels were similar in the two germfree groups at both 3 and 8 months of age, while serum T4 levels were again slightly but significantly higher in the germfree chemically defined diet group at both ages. Both T3 and T4 decline with age in conventional mice, but not in either germfree group, similar to findings in germfree rats. The data suggest that germfree mice fed chemically-defined diet require additional energy expenditure to effectively utilize its major dietary components.