Comparison of alpha2 adrenoreceptors on arterial smooth muscle and brain homogenates from spontaneously hypertensive and wistar-kyoto normotensive rats

Robert J. Weiss, R. Clinton Webb, Charles B. Smith

Research output: Contribution to journalArticle

17 Scopus citations

Abstract

Alpha2adrenoreceptors are located on vascular smooth muscle of the rat tail artery. In the present study this receptor was studied in spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats. Adrenergic agonists were used to produce isometric contractions of helically-cut tail artery strips from SHR and WKY. Clonidine and guanabenz, alpha2 agonists, were more potent in the SHR than in the WKY (e.g. clonidine: EC50SHR = 3.5 ± 0.6 × 10-8M; EC50WKY = 17.0 ± 0.2 × 10-8M; P < 0.0005). There was no difference in potency between the alpha! agonists, phenylephrine and methoxamine. Yohimbine, an alpha2antagonist, was more potent in inhibiting the clonidine-induced contraction in the SHR (pA2= 7.66 versus 7.14). To determine the number of alpha2 adrenoreceptors, the specific binding of3H-clonidine to homogenates of tail artery and of five brain areas was also measured. The maximum number of high-affinity sites on the tail artery was threefold greater in SHR than in WKY (31 ± 5 versus 11 ± 3 fmol/mg protein, P < 0.0005). No differences in the number or affinity of alpha2 receptor sites was found in the hypothalamus, hippocampus, locus coeruleus or parietal cortex of the two strains of rat. There was a difference in the amygdala (SHR: 163 ± 16 versus WKY: 108 ± 14, P < 0.05). The larger number of alpha2adrenoreceptors on the vascular smooth muscle in SHR may provide an explanation for the supersensitivity of SHR to adrenergic agonists.

Original languageEnglish (US)
Pages (from-to)249-255
Number of pages7
JournalJournal of hypertension
Volume2
Issue number3
DOIs
StatePublished - Jun 1984

Keywords

  • Clonidine
  • Hypertension
  • Norepinephrine
  • Rat tail artery
  • Yohimbine

ASJC Scopus subject areas

  • Internal Medicine
  • Physiology
  • Cardiology and Cardiovascular Medicine

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