Examination of medullary α2 receptors in connection with verapamil induced-hypotension

J. R. Holtman, M. T. Piascik

Research output: Contribution to journalArticlepeer-review

Abstract

The interaction of the phenylalkylamine calcium channel blocker, verapamil, at the alpha2 receptor in the cat brain was studied using radioligand binding and physiological techniques. Specific binding for [3H]yohimbine, a probe for the alpha2 receptor, was demonstrated in the medulla. The affinity and density of [3H]yohimbine sites were 1.62 Nm and 47 fmol/mg, respectively. Desmethoxyverapamil and the isomers of verapamil were able to displace specific [3H]yohimbine binding. Affinity estimates were 150 Nm for desmethoxyverapamil, 150 Nm for (-)verapamil and 480 Nm for (+)verapamil. We could not detect the presence of [3H]desmethoxyverapamil binding sites in the medulla. To assess the possible physiological role of binding at the alpha2 receptor in the medulla, verapamil was administered by the intracisternal route in the chloralose/urethane anesthetized cat and the effect on cardiovascular activity was determined. Verapamil (100-1000 nmol) was found to cause hypotension. Pretreatment with yohimbine (100 μg) did not block the verapamil-induced hypotension. The results demonstrate that central administration of verapamil has a hypotensive action. However, this effect does not appear to be due to an interaction at alpha2 receptors.

Original languageEnglish
Pages (from-to)59-66
Number of pages8
JournalNeuroscience Research Communications
Volume16
Issue number1
StatePublished - 1995

Keywords

  • Alpha receptors
  • Blood pressure
  • Calcium channel blockers
  • Cat

ASJC Scopus subject areas

  • Neuroscience (all)

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