Sympathetic Activity, Age, Sucrose Preference, and Diet‐Induced Obesity

Abstract

Only half the adult male Sprague‐Dawley rats which are placed on a diet relatively high in calories, fat, and sucrose (HE diet) develop diet‐induced obesity (DIO). The rest are diet‐resistant (DR). Some chowfed rats prone to develop DIO on an HE diet have greater initial food intake of this diet and all have greater glucose‐induced plasma norepinephrine (NE) increases than DR‐prone rats. Here we looked for a relationship of sucrose preference or 24‐hour urinary catecholamine excretion as possible phenotypic markers of the DIO‐ and DR‐prone states before HE diet exposure as a function of age. When begun on an HE diet at 3 months of age, DIO‐prone rats gained 30% more weight over 3 months than DR‐prone rats and had 35% heavier retroperitoneal fat pads. While still on chow, sucrose preferences were similar, but 24 hour urine NE levels were 29% higher in DIO‐than in DR‐prone rats. The slope of the curve of urine NE versus body weight gain after 3 months on HE diet was 4‐fold greater in DIO‐ thaain DR‐prone rats. After 3 months on the HE diet, there was no statistical relationship between 24‐hour urine NE and body weight or prior body weight gain in DIO or DR rats. Six‐month‐old DIO‐prone rats had 126% and 128% more urine NE and gained 112% and 232% more weight after 3 months on HE diet than DR‐prone and chowfed rats, respectively. Only DIO‐prone rats showed a correlation (r=0.879; p=O.OS) between urine NE levels and subsequent weight gain on HE diet. Thus, 3‐ or 6‐ month‐old DIO‐ and DR‐prone rats can be identified by their 24‐hour basal urine NE levels but not sucrose preference prior to HE diet exposure. While this may suggest higher basal sympathetic activity in DIO‐prone rats, other explanations are possible. (OBESITY RESEARCH 1993;1:281–287)