Adrenergic Vasomotion in the Coronary Microcirculation

  • William M. Chilian

Summary

The goal of this study was to determine the α-adrenergic receptor subtype(s) responsible for constriction at different microvascular levels in the coronary circulation. To accomplish these goals, the epicardial coronary microcirculation of intact beating hearts was viewed through an intravital microscope using stroboscopic epi-illumination. An initial study was designed to establish sites of α-adrenergic constriction to norepinephrine in preparations with intact vasomotor tone. For the primary experimental goal, coronary microvascular responses to selective α1-adrenergic (phenylephrine) or α2-adrenergic (BHT-933) agonists were evaluated, when coronary autoregulatory escape mechanisms were blunted during hypoperfusion. Infusion of norepinephrine decreased diameter of arterial vessels greater than 100μm in diameter, but downstream coronary arterioles dilated significantly, representing autoregulatory escape from adrenergic vasoconstriction. In studies designed to examine the adrenergic receptor subtype (during hypoperfusion), phenylephrine produced modest constriction of vessels throughout the microcirculation (6–9% decrease in diameter), whereas BHT-933 produced marked constriction of small coronary microvessels, those less than 100μm in diameter (24% decrease in diameter). From these results we conclude: 1) norepinephrine infusion causes disparate responses in the coronary microvasculature: constriction occurs in vessels greater than 100μm in diameter, but dilation, via autoregulatory escape, predominates in vessels less than 100μm in diameter; 2) α1-adrenergic receptors are located in coronary arterioles and arteries; and 3) α2-adrenergic receptors are preferentially located in small coronary arterioles. Thus, α1 - and α2-adrenergic activation can produce dissimilar constrictor effects in the coronary microcirculation during hypoperfusion.

Keywords

Ischemia Attenuation Norepinephrine Fluores Epinephrine 

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Copyright information

© Springer-Verlag Berlin Heidelberg 1991

Authors and Affiliations

  • William M. Chilian
    • 1
    • 2
  1. 1.Department of Medical Physiology, Microcirculation Research InstituteTexas A&M UniversityCollege StationUSA
  2. 2.Department of Medical PhysiologyTexas A&M University College of MedicineCollege StationUSA

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