The Effect of Phenylephrine upon Arterial Pressure, Carotid Sinus Radius and Baroreflex Sensitivity in the Conscious Greyhound

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Abstract
A method for recording carotid sinus diameter in conscious dogs was developed, using an ultrasound transit time technique. The distensibility of the carotid sinus in resting animals was measured, and the effect of injecting the vasoactive drug phenylephrine on the mechanical behavior of the sinus wall was investigated. Baroreflex sensitivity was measured in the dogs by the usual method of relating the slowing of the heart to the transient pressure rise induced by phenylephrine injections. Phenylephrine directly reduces the radius of the carotid sinus during the measurements of baroreflex sensitivity. At a dose of 2-4 .mu.g/kg, phenylephrine has an enhancing effect on the baroreflex response, possibly resulting from a modification of baroreceptor output.