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Effect of Gender on the Response to a High Fat Diet in Aging Fischer 344 Rats^1,2,

Roger B. McDonald^*,, Kristin Carlson^*,, Carolyn Day^*,, Judith S. Stern^*,, and Barbara A. Horwitz^**,

^* Department of Nutrition ^** Department of Animal Physiology Department of Internal Medicine The Food Intake Laboratory, University of California, Davis, CA 95616

The purpose of this study was to describe the effects of high fat (HF) and low fat (LF) diets in male and female Fischer 344 (F344) rats ages 5, 23 and 27 mo. Rats were fed the diet for 3 mo, and then resting metabolic rate, body composition and adipose tissue cell-ularity were evaluated. Although body mass was greater in rats fed the HF diet, this difference was due to a rapid increase in mass within the first 2 wk. There was no difference in the rate of body mass gain after this period. Resting mass-independent metabolic rate did not significantly differ due to age, diet or gender. In general, percentage fat mass was greater in rats fed the HF diet and in female than in male rats in both diet groups. However, lean body mass (%) was not altered due to diet or age. Cell number of the retroperitoneal depot increased with age and diet between 5 and 23 mo of age in both male and female rats. There was no effect of age, diet or gender on retroperitoneal cell size or gonadal cell number and size. These data suggest that age, gender and diet do not significantly alter the ability of F344 rats to regulate body composition or fat cell proliferation.

KEY WORDS: • adipose tissue • cellularity • body composition • sexual dimorphism • aging • metabolic rate • F344 rats

¹ Supported in part by grants from the National Institutes of Health, AG06665, DK32907 and SS-5P30 DK35747.

² We dedicate this article to the memory of Dr. Lucille S. Hurley, our good friend and esteemed colleague whom we miss dearly.

Manuscript received 25 May 1989. Revision accepted 1 August 1989.