Sl. Bealer, PREOPTIC RECESS ALPHA-ADRENOCEPTORS CONTROL CARDIOVASCULAR-RESPONSES TO HYPEROSMOLALITY, American journal of physiology. Regulatory, integrative and comparative physiology, 41(4), 1997, pp. 1283-1289
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
(alpha(1)- and era-antagonist), yohimbine (alpha(2)-antagonist), or pr
azosin (alpha(1)-antagonist) was perfused through microdialysis probes
in the DBB, AV3V, or lateral ventricle during a 30-min infusion of is
otonic (0.17 M; 0.1 or 1.7 ml.kg(-1).min(-1) iv) or hypertonic (2.5 M;
0.1 ml.kg(-1).min(-1) iv) NaCl. Hypertonic infusion increased blood p
ressure [mean arterial blood pressure (MAP); 17 +/- 2 mmHg] and decrea
sed 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 lat
eral ventricle did not alter either response. Stimulation of AVSV alph
a(1)-adrenoceptors (phenylephrine) decreased HR and MAP, whereas alpha
(2)-adrenoceptor stimulation (clonidine) produced bradycardia but incr
eased MAP. Data suggest that alpha-adrenoceptors in the AV3V, but not
the DBB, regulate cardiovascular responses to hyperosmolality.