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Regulation of Arterial Blood Pressure by Aortic Baroreceptors in the Unanesthetized Dog

We studied the effect of section of both carotid sinus nerves on arterial blood pressure in nine unanesthetized dogs. Four to seven recording sessions were conducted on each dog before and after sinus nerve section (SNS). During each session, histograms of mean arterial pressure during each heart cycle and of heart rate were assembled over 75 minutes. Then, responses to rapid aortic injection of nitroglycerin and phenylephrine were studied. Mean blood pressure was 94.86 ± 11.37 mm Hg with arterial baroreceptors intact. After SNS, mean blood pressure was 92.55 ± 9.82 mm Hg. Mean heart rate was 88.64 ± 11.97 beats/min in the intact dog and 86.20 ± 10.24 beats/min after SNS. Differences in mean blood pressure and heart rate were not significant (P > 0.05). The standard deviation of beat-by-beat mean arterial pressure was slightly, but not significantly, greater following SNS. The standard deviation of heart rate was slightly and significantly smaller (P < 0.02) after SNS. Blood pressure decreases following nitroglycerin were identical before and after SNS. There was a greater rise in blood pressure following phenylephrine after SNS. Heart rate changes following phenylephrine and nitroglycerin were smaller after SNS, but significant (P < 0.05) only for nitroglycerin. The dog with carotid sinus nerves sectioned regulates its mean blood pressure at the same level as the intact dog. Aortic baroreceptors reflexly compensate for both increased and decreased arterial pressure.