Effects of α-adrenoceptor antagonists and clonidine on the haemodynamic response to acute hypovolaemia in conscious rabbits

Roger G. Evans, Ian P. Hayes, John Ludbrook

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8 Citations (Scopus)


In conscious rabbits an inferior vena caval cuff was progressively inflated so cardiac output fell at a constant ∼ 8% of its baseline value. There was a biphasic haemodynamic response, consisting of an initial compensatory phase during which there was progressive systemic vasoconstriction and tachycardia, followed by a decompensatory phase in which systemic vasoconstriction failed abruptly, blood pressure plummeted and heart rate declined. We tested the effects on the haemodynamic response of prior 4th ventricular, and in some cases intravenous, infusions of saline, yohimbine, clonidine, yohimbine plus clonidine, and bunazosin. From the results we conclude that a yohimbine-sensitive mechanism in the brainstem, possibly α2-adrenoceptor-mediated, may be an essential element of the cardiac receptor-mediated decompensatory phase of acute central hypovolaemia, but does not contribute to the arterial baroreflex-mediated compensatory phase.

Original languageEnglish
Pages (from-to)265-272
Number of pages8
JournalEuropean Journal of Pharmacology
Issue number2
Publication statusPublished - 5 Jun 1992
Externally publishedYes


  • (Rabbit)
  • Baroreceptors
  • Clonidine
  • Haemorrhage
  • Yohimbine
  • α-Adrenoceptors

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