Long-term clonidine effects on autonomic function in essential hypertensive man

I. M. Cohen, D. T. O'Connor, R. A. Preston, R. A. Stone

Research output: Contribution to journalArticlepeer-review

15 Scopus citations


Acute studies of clonidine suggest that it lowers blood pressure by central enhancement of baroreflex sensitivity coupled with diminished evidence of sympathetic outflow, but longterm clonidine data have not been conclusive. We examined effects of one month of low dose clonidine (0.4 ± 0.15 mg/day) alone in 13 essential hypertensive men, assessing several biochemical indices of sympathetic function, as well as physiologic parameters, including baroreflex sensitivity, the cold pressor test, and the hypotensive response to alpha adrenergic blockade. Clonidine diminished mean arterial pressure (from 104±5 to 84±3 mmHg;p<0.01), without associated changes in several biochemical parameters of sympathetic outflow (urinary excretion of catecholamines, metanephrines, and vanillylmandelic acid; all p>0.1). Circulatory baroreflex function was not enhanced by clonidine, during either the amylnitrite test or the phenylephrine test, before or after parasympathetic blockade with atropine. The cold pressor test, an index of efferent sympathetic pressor function, was also unaltered. The enhanced mean arterial pressure response to phentolamine during clonidine therapy (from a fall of 14.8±4.3 to 39.4±5.2 mmHg, p<0.01), suggested an increase in alpha adrenergic vascular tone, perhaps mediated by clonidine's alpha agonist properties in vascular smooth muscle. The antihypertensive mechanism of longterm low dose clonidine cannot reliably be ascribed either to baroreflex enhancement or to suppression of sympathetic outflow.

Original languageEnglish (US)
Pages (from-to)25-32
Number of pages8
JournalEuropean Journal of Clinical Pharmacology
Issue number1
StatePublished - Jan 1 1981
Externally publishedYes


  • baroreceptor reflex
  • clonidine
  • hypertension
  • mode of action
  • sympathetic activity
  • urinary catecholamines

ASJC Scopus subject areas

  • Pharmacology, Toxicology and Pharmaceutics(all)
  • Pharmacology (medical)


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