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High Sucrose Diet and Exercise: Effects on Insulin-Receptor Function of 12- and 24-mo-old Sprague-Dawley Rats¹

Kristin C. Eiffert^*,2, Roger B. McDonald^* and Judith S. Stern^*,

^* Department of Nutrition Food Intake Laboratory and Division of Clinical Nutrition, University of California, Davis, CA 95616

The purpose of this study was to evaluate the effect of aging (12 vs. 24 mo) on skeletal muscle insulin receptor function of male Sprague-Dawley rats fed either a 33% sucrose (wt/wt) or sucrose-free diet. The effect of exercise in combination with the sucrose diet was also evaluated by exercising half of the sucrose-fed group on a motorized treadmill. Insulin-receptor function was assessed in vitro by measuring the binding capacity of [¹²⁵I]-insulin to partially purified receptors of the biceps femoris and vastus lateralis. Tyrosine kinase activity was measured as an index of postreceptor function. Insulin-receptor number was significantly decreased in 24-mo-old sucrose-fed rats compared to 12-mo-old rats fed the sucrose or sucrose-free diets. The affinity of insulin for the receptor did not significantly differ among groups. Maximal tyrosine kinase activity in vastus lateralis was significantly decreased in 12-mo-old sucrose-fed rats compared with sedentary 24-mo-old rats fed the sucrose-free diet or 24-mo-old rats fed the sucrose diet in combination with exercise. Exercise prevented the decrease in receptor function in both 12- and 24-mo-old sucrose-fed rats as measured by insulin binding and tyrosine kinase activity. These data suggest that diet and/or exercise rather than aging per se has a greater influence on insulin-receptor function.

KEY WORDS: • aging • insulin binding • insulin resistance • skeletal muscle • rats

¹ Supported in part by grants from the Nora Eccles Tredwell Foundation and National Institutes of Health AG06665, AG00429, DK35747, DK18899, DK07355.

² Supported by the Nestlé Corporation as the Nestlé Fellow in Nutrition and Aging.

Manuscript received 14 June 1990. Revision accepted 14 November 1990.