Norepinephrine applied in the paraventricular hypothalamic nucleus stimulates vasopressin release

The present experiments were designed to investigate the effect of norepinephrine (NE) applied directly in the area of the paraventricular nucleus (PVN) of the hypothalamus on arginine-vasopressin (AVP) release and blood pressure. A microinjection of 0.4 micrograms NE in the PNV produced a plasma AVP level of 26.3 +/- 5.3 pg/ml compared to 5.3 +/- 0.6 pg/ml in controls receiving dextrose (P less than 0.001). This rise was associated with blood pressure elevations varying between 10 and 13 mm Hg, lasting for about 5 min. Systemic injection of an antivasopressor AVP antagonist reversed or prevented the blood pressure rise induced by NE microinjection. The data suggest that locally applied NE in vasopressinergic neurons of the hypothalamus stimulates the release of AVP and induces an AVP-dependent rise in blood pressure.