Starvation reduces norepinephrine activities in both hypothalamus and heart in rats

Norepinephrine (NE) activities in both hypothalamus and heart were simultaneously assessed in rats after food-deprivation for 2 days. The technique of gas chromatography-mass spectrometry was employed for the analysis of NE and its primary neuronal metabolite, 3,4-dehydroxyphenylethylene glycol (DHPG), and the ratio of DHPG to NE was used as an index of NE activity. Hypothalamic DHPG/NE ratio was significantly decreased by fasting and was completely reversed by a single day of refeeding. These changes in hypothalamic DHPG/NE ratio were parallel to those in cardiac DHPG/NE ratio. Supporting the concept in which hypothalamic NE neurons play an important role in modulating the sympathetic outflow, it is suggested the decrease in hypothalamic NE activity contributes to the reduction in cardiac NE activity during fasting.