Hypothalamic levels and utilization of noradrenaline and 5-hydroxytryptamine in the sodium-depleted rat

The present report investigated the time course of hypothalamic noradrenaline (NA) and 5-hydroxytryptamine (5-HT) metabolism in male rats with acute sodium depletion by intraperitoneal dialysis (IPD). The hypothalamic level and utilization of NA start to rise significantly 12 to 24 hrs after IPD. In contrast, 24 hrs after IPD, sodium-depleted rats allowed to drink sodium in a half hour drinking test significantly decreased NA steady state and utilization. Electrochemical stimulation of the pre-limbic cortex 5 hrs after IPD significantly increased the utilization but not the concentration of NA, whereas sodium replenishment decreased both of them. The metabolism of hypothalamic 5-HT was not affected 12-24 hrs after sodium depletion or by electrochemical stimulation, while both the levels of 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) increased significantly in sodium-depleted rats allowed to drink sodium. These results suggest that sodium deficiency promotes an increased hypothalamic NA utilization while failing to affect 5-HT metabolism.