Effects in the rat of environmental temperature, diet dilution and treadmill running on voluntary food intake, body composition and endocrine organ mass: a multiple regression analysis.

The effects upon weight gain, food intake, carcass composition, and weight of pituitary, adrenals, and testes of male rats subjected to three environmental temperatures (T; 16.0 degrees, 23.5 degrees, and 31.0 degrees), five diet dilution rates (D; 0%, 12.5% 25.0%, 37.5%, and 50.0%), and five daily treadmill running periods (E; 10 minutes, 40 minutes, 70 minutes, 100 minutes, and 130 minutes) were studied by multiple regression techniques. Equations describing regression surfaces could contain significant linear and/or quadratic coefficients of the independent variables (T, D, and E) and their first order interactions. Body weight attained was reduced by increased D and T. Total food intake increased linearly with increases in D, but this increase was smaller for the rats in the higher environmental temperature since there was a significant DT interaction. Total food intake was decreased by increases in T. The intake of food minus diluent was maintained until D attained a value of 37.5%; beyond this point the rats at all three temperatures failed to maintain digestible energy intake. The data strongly suggested that the energy intake was not limited by the gastrointestinal tract capacity. E did not significantly affect food intake. Significant regression coefficients were found for the dependent variables of body dry matter, nitrogen, ash, ether extract, and energy and of the weight of depot fat pads, adrenals, and testes, as follows: (1) For D, there was no linear coefficient for body nitrogen. All remaining linear coefficients were negative except for body ash. The only quadratic coefficients (both positive) were for adrenal and testes weights (2) For E, all linear coeffcients were negative except those for body nitrogen, body ash, and adrenal weight. There were not quadratic coefficients for body nitrogen, body ash, adrenal weight, and testes weight. The remaining quadratic coefficients were all positive; (3) For T, there was no quadratic coefficient for body energy. The remaining linear coefficients were positive except those for fat deposit size, body ether extract, and adrenal weight. The remaining quadratic coefficients were negative except those for fat deposit size, body ether extract, and adrenal weight; (4) For the DE interaction, no coefficients were significant; (5) For the DT interaction, there were no significant coefficients for body nitrogen, fat depot size, or adrenal weight. The remaining coefficients were positive except for body ash; (6) For the ET interaction, the only significant coefficients were negative ones for body ether extract and body energy and a positive one for testes weight.