Regional vascular influences on tail-cuff measurements of drug-induced changes in systolic pressure

When drug effects are quantified using the tail-cuff method, changes in systemic arterial pressure are extrapolated from those occurring in the caudal artery. The validity of this extrapolation was tested in anesthetized rats by recording drug-induced changes in phasic arterial pressure simultaneously from catheters inserted into the lower abdominal aorta, carotid, and caudal arteries. Pressor responses to norepinephrine or angiotensin were of equal magnitude at all three sites, but phentolamine reduced systolic pressure in the aorta or caudal artery more than that in the carotid artery. Unlike previous discrepancies between carotid and tail-cuff systolic pressures, aortic hypotension caused by injections of phentolamine or pentolinium in awake normotensive or spontaneously hypertensive rats was accurately predicted by the tail-cuff method. Because drug-induced changes in diastolic pressure always varied much less than those in systolic pressure, should indirect measurement of diastolic pressure become technically feasible, it might be preferable for assessing drug effects on blood pressure.