Effects of azepexole and clonidine on baroreceptor mediated reflex bradycardia and physiological tremor in man.

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Abstract
The effects of oral administration of azepexole 10 mg, clonidine 300 micrograms and placebo on baroreceptor mediated reflex bradycardia and physiological tremor were investigated in six healthy volunteers. Both azepexole and clonidine reduced (P less than 0.05) systolic (120.5 +/‐ 2.5 to 105.0 +/‐ 3.3 mm Hg; 115.8 +/‐ 2.6 to 104.7 +/‐ 2.8 mm Hg respectively) and diastolic (52.5 +/‐ 2.6 to 47.2 +/‐ 1.4 mmHg; 53.7 +/‐ 1.6 to 49.0 +/‐ 1.5 mmHg respectively) pressure when compared to placebo and to pre‐treatment values. This reduction in pressure was not accompanied by a change in heart rate. Both azepexole and clonidine enhanced (P less than 0.05) baroreflex sensitivity to increases in systolic arterial pressure with phenylephrine. Clonidine facilitated (P less than 0.05) baroreflex sensitivity during the strain phase of the Valsalva manoeuvre, whereas azepexole reduced it (P less than 0.05). Neither clonidine nor azepexole altered finger tremor when compared to placebo or pre‐treatment values. Azepexole produced (P less than 0.05) sedation compared to placebo but not when compared to pre‐treatment values. Clonidine caused significant increases in sedation when compared to both placebo and to pre‐treatment values. The differences between azepexole and clonidine may be due to the greater specificity of azepexole for the alpha 2‐adrenoceptor than clonidine.