Catecholamines and serotonin in the area postrema of normal and sodium-depleted dogs

Sodium depletion, a maneuver that is accompanied by a 14-fold elevation of plasma renin activity (PRA), alters the norepinephrine concentration of the canine area postrema (AP), a circumventricular organ of the 4th ventricle known to be sensitive to circulating angiotensin II. The norepinephrine concentration of the AP after 3 weeks of sodium depletion decreased by 43%, whereas the concentration of epinephrine and dopamine and the activity of phenylethanolamine-N-methyltransferase (PNMT) did not change. In the pyramidal tract (PT) and choroid plexus (CP) catecholamines were present in significantly lower amounts than in the AP; their concentrations were unaffected by sodium depletion in the PT, but in the CP the norepinephrine concentration was reduced. Serotonin was present in the AP but its concentration was unaltered by sodium depletion. These findings provide evidence that sodium depletion produced an alteration in the concentration of norepinephrine of the area postrema without any change in the concentration of epinephrine, dopamine or serotonin.