Preoptic recess alpha-adrenoceptors control cardiovascular responses to hyperosmolality

Abstract

The roles of alpha-adrenoceptors in the anteroventral third ventricle (AV3V) and diagonal band of Broca (DBB) in cardiovascular responses to peripheral hypertonicity were investigated in conscious rats. Normal artificial cerebrospinal fluid (aCSF) or aCSF containing phentolamine (alpha1- and alpha2-antagonist), yohimbine (alpha2-antagonist), or prazosin (alpha1-antagonist) was perfused through microdialysis probes in the DBB, AV3V, or lateral ventricle during a 30-min infusion of isotonic (0.17 M; 0.1 or 1.7 ml x kg(-1) x min(-1) i.v.) or hypertonic (2.5 M; 0.1 ml x kg(-1) x min(-1) i.v.) NaCl. Hypertonic infusion increased blood pressure [mean arterial blood pressure (MAP); 17 +/- 2 mmHg] and decreased heart rate (HR; 36 +/- 6 beats/min). Both responses were abolished by AV3V administration of phentolamine or yohimbine, whereas prazosin selectively prevented the bradycardia. Phentolamine in the DBB or lateral ventricle did not alter either response. Stimulation of AV3V alpha1-adrenoceptors (phenylephrine) decreased HR and MAP, whereas alpha2-adrenoceptor stimulation (clonidine) produced bradycardia but increased MAP. Data suggest that alpha-adrenoceptors in the AV3V, but not the DBB, regulate cardiovascular responses to hyperosmolality.