ANGIOTENSIN-II NEUROTRANSMITTER ACTIONS IN PARAVENTRICULAR NUCLEUS ARE POTENTIATED BY A NITRIC-OXIDE SYNTHASE INHIBITOR

There is increasing evidence that nitric oxide (NO) plays a role withi n the central nervous system as a novel messenger. Neuronal culture wo rk suggests NO to be involved specifically in mediating actions of ang iotensin II (ANG). The present study examined the potential role of NO within the paraventricular nucleus (PVN), a structure involved in med iating the cardiovascular changes initiated by activation of the subfo rnical organ (SFO). The presser response to stimulation of SFO, which can be divided into a short (SD) and long duration (LD) component was enhanced following administration of an NO synthase inhibitor (L-NAME) (SD control: 101 +/- 4 vs. post L-NAME: 145 +/- 10 mmHg.s (P<0.05); L D control: 387 +/- 167 vs. post L-NAME: 1737 +/- 617 mmHg.s (P<0.05)). This effect was specific to activation of SFO efferents as the blood pressure responses to either, stimulation of PVN, or systemic administ ration of vasopressin were not potentiated by administration of L-NAME . These findings suggest that NO may be acting within PVN to inhibit f urther release of ANG, thereby attenuating the cardiovascular response to stimulation of SFO.