Genetic influence on nutritional aspects of metabolic regulation I.

Examples of two genetic models of growth and development are described. Mice selected for growth rate from 3 to 6 weeks of age show an increase in mature body size and an increase in tissue cellularity. Manipulation of dietary intake at various ages resulted in different responses in the control and growth strain mice. Futher trials are needed to determine metabolic or endocrine adaptations that are responsible for enhanced growth in these mice. The second model discussed was the genetically obese Zucker rat. When compared to its lean littermates, the obese rat is hyperphagic and metabolically efficient in storing calories as fat, and has impaired development of muscle tissue. The shift in the growth of muscle tissue to the growth of adipose tissue cannot be prevented by dietary manipulation or exercise. Increases in liver lipogenic rate can be prevented by feeding a high fat diet. It appears from the nutritional studies presented hear that many of the metabolic lesions associated with the development of spontaneous obesity in this animal model are secondary to the primary causal event.