Drinking decreases the noradrenaline release in the median preoptic area caused by hypovolemia in the rat.

Previous observations have suggested that the noradrenergic system in the median preoptic nucleus (MnPO) is implicated in the regulation of body fluid balance and cardiovascular function. The present study was carried out to investigate whether water intake alters the release of noradrenaline (NA) in the MnPO area caused by hypovolemia in freely moving rats. Nonhypotensive hypovolemia was induced by subcutaneous polyethylene glycol (PEG), and extracellular levels of NA were measured using intracerebral microdialysis techniques. Subcutaneous injections of PEG (30%, 5 ml) significantly enhanced the NA release in the MnPO area. Water ingestion significantly attenuated the elevation in the NA release in the MnPO area induced by the PEG treatment. These results show the involvement of the noradrenergic system in the MnPO in the maintenance of body fluid volume, and suggest that the system may play an important role in the elicitation of hypovolemia-induced dipsogenic response.