Vol. 273, Issue 4, H1713-H1718, October 1997
-Adrenoceptors in vascular capacitance responses to
unloading of carotid baroreceptors in anesthetized dogs
F.
Karim and
S. M.
Poucher
Department of Physiology, University of Leeds, Leeds LS2 9JT, United
Kingdom
The role of 
- and 
-adrenoceptors in the
total vascular capacitance responses to changing pressure in vascularly
isolated carotid sinuses of anesthetized and atropinized dogs was
investigated. A change in vascular capacitance was determined by
measuring the shift of blood in and out of a reservoir that was
connected to the aorta and maintained at a constant pressure. Changes
in carotid sinus pressure from 135 to 57 mmHg and back to 137 mmHg
resulted in a rapid vascular capacitance response of ~30 ml in the
absence of adrenoceptor antagonists. Administration of a
2-adrenoceptor antagonist
(ICI-118551) caused a significant enhancement of the capacitance
responses to similar decreases and increases in carotid sinus pressure
(~130%). Administration of a
1-adrenoceptor antagonist (CGP-20712A) did not cause any further enhancement of the responses. However, an -blocker (phentolamine) reduced the responses by 75%.
The results suggest that in the presence of a
2-adrenoceptor antagonist
vascular capacitance responses to loading and unloading of
baroreceptors are greatly enhanced and that patients suffering from
orthostatic syncope may benefit from this kind of drug.
-blocker; -blocker
