Effects of energy restriction on norepinephrine turnover and serum glucose and fatty acids in lean mice

Abstract

Norepinephrine (NE) turnover rate was determined in several tissues of 5-week-old female mice fed a high carbohydrate diet (58% of energy as carbohydrate, 30% fat) either ad lib or restricted to 34 or 24 kJ/day (36 to 50% restriction) presented as 1 or 2 daily meals. When the restricted intakes were divided into 2 equal meals, daily NE turnover did not differ from that of ad lib-fed mice. When the above restricted amounts were provided as a single daily meal at the beginning of the dark period, NE turnover was 38% and 46% lower, respectively, in the heart only compared to ad lib-fed controls. Serum glucose and total free fatty acids were affected by dietary conditions known to produce sympathetic activation (high carbohydrate and high fat diets) and suppression (high protein diet and energy restriction as a single meal), but the changes were unrelated to fractional NE turnover. Thus, the lower NE turnover seen when food intake is restricted is due to the prolonged overnight fast and not due to the lower energy intake per se, and is not associated with serum concentration of glucose or total free fatty acids.