alpha 1-adrenoceptor activation can increase heart rate directly or decrease it indirectly through parasympathetic activation

British Journal of Pharmacology
N A Flavahan, J C McGrath

Abstract

1 The chronotropic effects of alpha- and beta-adrenoceptor agonists were investigated in the pithed rat. 2 The beta-adrenoceptor agonist, isoprenaline, produced only a positive chronotropic response. alpha 1-Adrenoceptor agonists, phenylephrine and amidephrine, produced positive and negative chronotropic effects. Part of the response to phenylephrine was beta-mediated. 3 A positive chronotropic response to amidephrine and phenylephrine was mediated directly through cardiac alpha 1-adrenoceptors and had a different time course from beta-adrenoceptor-mediated responses. 4 A negative chronotropic response to alpha-agonists was potentiated by neostigmine and blocked by atropine, tetrodotoxin or hexamethonium as well as by alpha 1-adrenoceptor antagonists. This may indicate alpha 1-adrenoceptors on preganglionic parasympathetic nerves, stimulation of these receptors causing release of acetylcholine. 5 The alpha 2-adrenoceptor agonist, xylazine, produced a direct negative chronotropic effect on the heart, independent of alpha-adrenoceptors. No evidence was found for functional post-junctional alpha 2-adrenoceptors. At high doses xylazine stimulated cardiac alpha 1-adrenoceptors.

References

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Citations

Jun 1, 1985·Naunyn-Schmiedeberg's Archives of Pharmacology·G Gross, I Lues
Nov 1, 1987·Pflügers Archiv : European journal of physiology·P BorgdorffA Cevese
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Nov 5, 2016·Toxicon : Official Journal of the International Society on Toxinology·Lourdes DiasStephen Hyslop
Oct 1, 1989·Medicinal Research Reviews·J C McGrathV G Wilson
Jan 1, 1990·Life Sciences·B G Benfey

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