Enhanced saline intake and decreased heart rate after area postrema ablations in rat

The area postrema (AP) is a circumventricular organ located in the dorsal medulla. Previous studies found that AP lesions lead to increased saline ingestion in the rat. The salt appetite was thought to be a result of primary disruptions in sodium regulation or in cardiovascular regulation. To assess this we measured food and fluid intakes, urinary electrolyte and aldosterone concentration, and blood pressure and heart rates in AP lesioned and control animals during a period of normal sodium intake and during a period of excessive sodium intake. Rats with AP lesions exhibited sodium appetite but not natriuresis. In fact, sodium intake greatly exceeded output. Their urinary aldosterone levels were similar to those of control animals during both periods. The lesioned rats also had lowered heart rates, yet, their blood pressures were similar to control animals. These results are discussed with reference to a possible role of the AP in satiety and in maintaining homeostasis.