Contribution of body weight and growth to risk of anterior pituitary gland tumors of the rat.

The dietary and growth histories of noninbred male Charles River COBS rats permitted freedom of dietary choice throughout life were analyzed to determine the conditions associated with the spontaneous occurrence of anterior pituitary gland tumors (PT). The animals were allowed to regulate their protein intake apart from energy intake. Multivariable models were derived distinguishing rats that develop PT from those remaining free of tumors throughout life. Conventional fixed diet studies suggested that the quantity and quality of the diet consumed would be the best explanatory variables. However, body weight-related variables were found to be more important. The interacting, time-related conditions conductive to a high probability of PT occurrence included an unusually high growth rate associated with a high level of conversion of the food consumed into body mass during early life and a high intake of protein relative to body weight during early adult life. The accuracy in identifying rats with PT was even greater if mature body weight was included as an explanatory variable.