PARAVENTRICULAR NUCLEUS HISTAMINE INCREASES BLOOD-PRESSURE BY ADRENOCEPTOR STIMULATION OF VASOPRESSIN RELEASE

The role of adrenoreceptor stimulation and the peripheral mechanism me diating the increase in mean arterial blood pressure (MAP) and heart r ate (HR) during administration of histamine (HA) in the paraventricula r nucleus/anterior hypothalamus (PVN/AH) was evaluated in conscious ra ts. HA administered through microdialysis probes in the PVN/AH region increased MAP (18 +/- 1 mmHg) and HR (81 +/- 10 beats/min). The presso r response was abolished by simultaneous administration of phentolamin e (alpha(1)- and alpha(2)-antagonist) or prazosin (alpha(1)-antagonist ) but not altered by yohimbine (alpha(2)-antagonist). The tachycardia was not effected by any adrenergic antagonist. Furthermore, ganglionic blockade did not reduce the increase in MAP (21 +/- 2 mmHg) during PV N/AH perfusion with HA, while V-1-vasopressin receptor blockade abolis hed the presser response (4 +/- 2 mmHg). These data suggest that HA ad ministered to the PVN/AH increases blood pressure by local release of norepinephrine and alpha(1)-adrenoreceptor stimulation of vasopressin secretion, while the tachycardia is not mediated by alpha-adrenorecept ors.