Angiotensin ii modulates arterial baroreflex function via a central a-1 adrenoceptor mechanism in rabbits. Nishida, Yasuhiro, Kathy L. Ryan, and Vernon S. Bishop. Department of Physiology, The University of Texas Health Science Center, 7703 Floyd Curl Drive, San Antonio, Texas 78284-7756
APStracts 2:0041R, 1995.
To test the hypothesis that angiotensin II (ANG II) modulates arterial baroreflex function via a central [alpha]-1 adrenoceptor mechanism, we examined the effects of intravertebral infusion of ANG II on baroreflex function curves before and after intravertebral administration of the [alpha]-1 adrenoreceptor antagonist, prazosin. Rabbits were chronically instrumented with subclavian and vertebral arterial catheters, venous catheters and aortic and vena caval occluders. Baroreflex curves were obtained by relating heart rate (HR) to mean arterial pressure (MAP) during increases and decreases in arterial pressure. Intravertebral infusions of ANG II (5, 10 and 20 ng/kg/min) produced a dose-dependent shift of the mid range of the curve toward higher pressures (64 +/- 1 to 68 +/- 1, 76 +/- 1, 85 +/- 2 mmHg, respectively). Pretreatment with prazosin (10 [mu]g/kg) via the vertebral artery markedly reduced the shift in the baroreflex curve induced by the highest dose of ANG II (64 +/- 2 to 70 +/- 2 mmHg). These data suggest that ANG II resets the operating point of the HR baroreflex curve to a higher blood pressure and that this effect is mediated via a central [alpha]-1 mechanism. When the effects of vertebral ANG II on the baroreflex control of renal sympathetic nerve activity (RSNA) were examined, intravertebral administration of ANG II, while reducing the gain and the maximum RSNA, did not reset the RSNA baroreflex curve. These data suggests that ANG II acutely resets the HR baroreflex but not the RSNA baroreflex and that the resetting involves an a-1 adrenergic mechanism. 

Received 3 March 1994; accepted in final form 6 February 1995.
APS Manuscript Number R104-4.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 25 February 1995.