Role for the subfornical organ in vasopressin release.

The effect of subfornical organ (SFO) lesions on plasma vasopressin and drinking was tested in rats given either of two stimuli: subcutaneous injection of hypertonic saline or injection of a single dose of angiotensin II (AII) into the dorsal third cerebral ventricle. Drinking in response to hypertonicity was significantly attenuated, whereas AII-induced drinking was unaffected by the lesions. In contrast, SFO lesions were associated with significantly reduced vasopressin responses following either of these potent stimuli to vasopressin secretion. Partial lesions that damaged structures adjoining the SFO (fornix or septum) had no significant effects. These results demonstrate that, in rats, the SFO is in some way necessary for vasopressin responses to both AII and hypertonicity.