ANGIOTENSIN-II PRESSOR ACTIVITY DEPENDS ON MEDIAL AND LATERAL ANTERIOR HYPOTHALAMIC PATHWAYS

The preoptic region of hypothalamus was disconnected from caudal struc tures with two different-size knife cuts in rats to investigate the pa thway responsible for the effects of intracerebroventricular (ICV) and intravenous (IV) angiotensin II (ang II) on blood pressure and argini ne vasopressin (AVP) release. Seven clays after surgery ICV ang II (12 5 ng) in sham-operated (sham) rats increased mean arterial pressure (M AP) (+23 +/-3 mmHg) and decreased heart rate (HR) (-58 +/-5 beats/minu te). However, ICV ang II had no effect on MAP or HR of rats with a lar ge (preoptic-hypothalamic disconnection) cut. Both the presser respons e (+12 +/-2 mmHg) and the bradycardia (-39 +/-6 beats/minute) were sig nificantly reduced by a small (medial preoptic-hypothalamic disconnect ion) cut. The increased plasma AVP to ICV ang II in sham rats (9.8 +/- 3.6 pg/mL) was abolished in large-cut rats and attenuated in small-cut rats (3.2 +/-0.7 pg/mL). IV bolus injection of ang II (125 ng) in sha m rats increased MAP by 43 mmHg, whereas large-cut rats showed a blunt ed (25%) presser response. The presser response to nr infusion of ang II (8 ng/20 mu L/minute for 15 minutes) was diminished in large-cut ra ts (+4 +/-1 mmHg)as compared with that in sham rats (+19 +/-2 mmHg). B oth cuts transected the projection between the periventricular tissue surrounding the anteroventral third ventricle and supraoptic nucleus, but the supraoptic-neurohypophyseal pathway was severed only by the la rge cut. By examining the location of microknife cuts, the authors con clude that the connectivity of the preoptic region with more caudal si tes is necessary for the expression of the central and peripheral pres ser activity of ang II, probably involving a key role of supraoptic nu cleus and its connections.