THE activity of the sympathetic nervous system in the rat is markedly reduced by 2 d of fasting, and this suppression is reversed by feeding 1. Studies of urinary catecholamine excretion in fasting rats have corroborated these findings and in addition have shown that urinary adrenaline and noradrenaline (NA) excretion actually exceed baseline levels on the second and third days of refeeding2. Since dietary intake in these previously fasted animals was greater than baseline during the refeeding period, the possibility arose that overfeeding might be associated with increased sympathetic activity and led to the present investigation. Work by others has provided evidence that supplementation of a standard rat chow diet with sucrose-containing drinking solutions increases total caloric intake of the rat by approximately 20%3. Thus the experimental design for voluntary overfeeding in the rat is based on the addition of sucrose-containing drinking solutions to the animals's; ad libitum access to rat chow and water during the experimental period. In this report we describe increased sympathetic activity in the hearts of overfed animals after 3d of sucrose supplementation. Such an increase in sympathetic activity may contribute to the enhanced thermogenesis associated with overfeeding.
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