Beta-adrenoceptors in vascular capacitance responses to unloading of carotid baroreceptors in anesthetized dogs.
The role of beta- and alpha-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 approximately 30 ml in the absence of adrenoceptor antagonists. Administration of a beta2-adrenoceptor antagonist (ICI-118551) caused a significant enhancement of the capacitance responses to similar decreases and increases in carotid sinus pressure (approximately 130%). Administration of a beta1-adrenoceptor antagonist (CGP-20712A) did not cause any further enhancement of the responses. However, an alpha-blocker (phentolamine) reduced the responses by 75%. The results suggest that in the presence of a beta2-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.
Karim
F
F
Department of Physiology, University of Leeds, United Kingdom.
Poucher
S M
SM
D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002339:Carotid Arteries / Q000294:innervation*; D002346:Carotid Sinus / Q000187:drug effects / Q000502:physiology; D004285:Dogs; D006339:Heart Rate / Q000187:drug effects; D007093:Imidazoles / Q000494:pharmacology; D011311:Pressoreceptors / Q000502:physiology*; D011412:Propanolamines / Q000494:pharmacology; D011943:Receptors, Adrenergic, beta / Q000502:physiology*; D018924:Vascular Capacitance / Q000187:drug effects / Q000502:physiology*
D000319:Adrenergic beta-Antagonists; D007093:Imidazoles; D011412:Propanolamines; D011943:Receptors, Adrenergic, beta; C026777:ICI 118551; C049763:CGP 20712A