Baroreflex sensitivity in conscious rats: the influence of recording site

Arterial blood pressures were measured simultaneously in the thoracic and abdominal aortas in the same conscious rats. Intravenous administration of sodium nitroprusside caused a greater fall in systolic blood pressure in the abdominal aorta than in the thoracic aorta, whereas intravenous administration of methoxamine caused a greater rise in systolic blood pressure in the thoracic aorta. Hence baroreflex sensitivities derived from these data (by relating systolic blood pressure to the pulse interval of the succeeding beat) were appreciably different depending on the site of measurement. The changes in diastolic and mean arterial blood pressures induced by the drugs were similar at the two recording sites. It is suggested therefore that cardiac baroreflex sensitivity should be assessed in conscious rats by relating pulse interval to mean arterial blood pressure recorded at a site other than the thoracic aorta since cannulation at that site impairs baroreflex responsiveness.