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Related Experiment Videos

Cardiac alpha-adrenoceptors: postjunctional and prejunctional.

M J Rand, L H Tung, W J Louis

    Journal of Molecular and Cellular Cardiology
    |November 1, 1986
    PubMed
    Summary

    Postjunctional alpha-1 adrenoceptors increase heart rate via calcium influx. Prejunctional alpha-1 and alpha-2 adrenoceptors regulate noradrenaline release, impacting drug effects.

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    Area of Science:

    • Pharmacology
    • Cardiovascular Physiology

    Background:

    • Postjunctional alpha-adrenoceptors mediate positive inotropic and chronotropic effects.
    • Alpha-1 adrenoceptor activation leads to positive chronotropic responses when beta-adrenoceptors are blocked.

    Purpose of the Study:

    • To characterize the subtype and mechanism of postjunctional alpha-adrenoceptors mediating chronotropic responses.
    • To investigate the role of prejunctional alpha-adrenoceptors in regulating noradrenaline release.

    Main Methods:

    • Utilized pithed rat and isolated rat atria models.
    • Administered various alpha-adrenoceptor agonists and antagonists.
    • Manipulated calcium concentrations and used calcium channel modulators.

    Main Results:

    • Postjunctional alpha-adrenoceptors were identified as the alpha-1 subtype, with a potency order of adrenaline > noradrenaline > phenylephrine > methoxamine.
    • Alpha-1 adrenoceptor activation increases calcium influx, contributing to positive chronotropic effects.
    • Prejunctional alpha-1 and alpha-2 adrenoceptors modulate noradrenaline release, with prazosin and idazoxan enhancing release.

    Conclusions:

    • Postjunctional alpha-1 adrenoceptors mediate cardiac chronotropy through calcium channel activation.
    • Prejunctional alpha-adrenoceptors play a dual role in regulating noradrenergic neurotransmission.
    • Blockade of postjunctional alpha-1 adrenoceptors may increase noradrenaline release, complicating therapeutic outcomes.

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