title: The effects of clonidine on cardiovascular responses to standing in healthy volunteers.
abstract: This study assessed the effects of clonidine on blood pressure (BP) and heart rate responses to active standing, recorded continuously using a Finapres monitor. Ten subjects were given a placebo infusion over 1 h, followed by clonidine hydrochloride 1.5 micrograms/kg over 2 h. During placebo and at 1, 3 and 19 h following the clonidine infusion, heart rate and blood pressure were recorded during the second half of supine rest for 10 min, active standing and quiet standing for 7 min. Clonidine did not alter the size of immediate drop in BP on standing, although the nadir was lower. BP recovery was impaired, with a loss of the usual BP overshoot in most subjects and with delays in reaching supine levels of diastolic BP (6.1 versus 9.6 s; p < 0.01) and systolic BP (8.1 versus 12.3 s; p < 0.05). The compensatory initial heart rate rise was significantly increased from 47 to 53 beats/min (p < 0.05), although the peak rate reached was reduced from 114 to 104 beats/min (p < 0.05). These results demonstrate that impairment of central sympathetic vasomotor drive leads to a delay in BP recovery and loss of initial BP overshoot immediately after standing, together with impaired maintenance of early steady-state BP.
authors.affiliation: PsychoPharmacology Unit, University of Bristol, UK.
authors.forename: N J
authors.initials: NJ
authors.lastname: Coupland
authors.forename: J E
authors.initials: JE
authors.lastname: Bailey
authors.forename: S J
authors.initials: SJ
authors.lastname: Wilson
authors.forename: R
authors.initials: R
authors.lastname: Horvath
authors.forename: D
authors.initials: D
authors.lastname: Nutt
mesh_terms: D000328:Adult; D001794:Blood Pressure / Q000187:drug effects*; D003000:Clonidine / Q000494:pharmacology*; D005260:Female; D006339:Heart Rate / Q000187:drug effects*; D006706:Homeostasis; D006801:Humans; D008297:Male; D008991:Monitoring, Physiologic; D011187:Posture; D012016:Reference Values; D016683:Supine Position; D013997:Time Factors
chemical_list: D003000:Clonidine