Several changes in response to hormones and other biochemical stimuli have been associated with the aging process. However, in most mammalian species, aging occurs simultaneously with the deposition of body fat and this increase in body fat (increased adiposity and eventually obesity) has itself been associated with alterations in metabolism and response to hormones. Existing animal models have not been standardized enough to separate the effects of aging from those of variable adiposity. It is the goal of the current project to 1) establish and characterize an aging animal model (the rat) in which the degree of adiposity is controlled by dietary regulation; 2) to determine in this model the effects of aging on several morphological parameters, metabolic functions, hormone binding and hormone responsiveness in adipose and other tissues; and 3) to compare in animals of similar age, but differing degrees of adiposity, the alterations in cellularity, morphology, metabolism and hormonal responsiveness of adipose and other tissues in relation to the degree of adiposity. In this fashion, the effects of adiposity alone and aging alone can be analyzed.