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THE EFFECT OF THE CAROTID SINUS REFLEX ON LARGE CORONARY ARTERY DIAMETER IN ANAESTHETIZED DOGS
Author(s) -
Woodman Owen L.
Publication year - 1987
Publication title -
clinical and experimental pharmacology and physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 103
eISSN - 1440-1681
pISSN - 0305-1870
DOI - 10.1111/j.1440-1681.1987.tb02423.x
Subject(s) - medicine , coronary sinus , phentolamine , cardiology , propranolol , heart rate , blood pressure , artery , reflex , anesthesia , vascular resistance , coronary circulation , blood flow
SUMMARY 1. The diameter of, and blood flow in, the left circumflex coronary artery was measured in anaesthetized dogs and the carotid sinus reflex was stimulated by bilateral occlusion of the carotid arteries (BCO) for 2 min. 2. The effect of BCO on coronary artery diameter and late diastolic coronary resistance was examined: (a) after bilateral vagotomy; (b) after vagotomy plus antagonism of β‐adrenoceptors with propranolol (1 mg/kg, i. v.); and (c) after vagotomy, antagonism of β‐adrenoceptors and antagonism of α‐adrenoceptors with phentolamine (0.5 mg/kg, i.v.). 3. After vagotomy BCO increased mean arterial pressure (Δ= 72 ± 7 mmHg), heart rate (16 ± 3 beats/min), coronary blood flow (37 ± 11 ml/min) and coronary artery diameter (0.14 ± 0.04 mm). Late diastolic coronary resistance initially fell (‐0.26 ± 0.13 mmHg min/ml at 30s) but at the end of the 2 min occlusion it had returned to the baseline level (Δ= 0.04 ± 0.08 mmHg min/ml). 4. In the presence of propranolol BCO increased arterial pressure (28 ± 12 mmHg), but did not alter heart rate (0.6 ± 0.4 beats/min) or coronary blood flow (2 ± 2 ml/min). There was a significant decrease in large artery diameter (‐0.24 ± 0.07 mm) and an increase in late diastolic coronary resistance (0.46 ± 0.12 mmHg min/ml). A mechanical increase in afterload did not affect large coronary artery diameter or coronary resistance 5. Antagonism of α‐adrenoceptors abolished the reflex‐induced constriction of the large coronary artery (Δ= ‐0.02 ± 0.02 mm) and the coronary resistance vessels (ΔLDCR = ‐0.02 ± 0.03 mmHg min ml). 6. In conclusion, in the anaesthetized, vagotomized dog BCO induces vasodilatation of the large coronary artery which is reversed to a vasoconstriction by antagonism of β‐adrenoceptors. Antagonism of α‐adrenoceptors abolishes the BCO‐induced constriction of the large coronary artery and the coronary resistance vessels. These findings suggest that the tone of the large coronary arteries, as well as the coronary resistance vessels, may be regulated by neural reflexes.