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Biphasic pressor responses to norepinephrine in humans

K Sato1, M Sawada, M Kojima

  • 1Second Department of Internal Medicine, Nagoya City University Medical School, Japan.

Clinical Pharmacology and Therapeutics
|November 1, 1995
PubMed
Summary

Norepinephrine causes a biphasic pressor response, with the late phase mediated by calcium influx via nicardipine-sensitive channels. Alpha-blockers like phentolamine and prazosin affect both phases.

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Area of Science:

  • Pharmacology
  • Cardiovascular Physiology

Background:

  • Norepinephrine is a critical endogenous catecholamine and neurotransmitter.
  • Understanding its pressor effects and mechanisms is vital for cardiovascular research.

Purpose of the Study:

  • To investigate the biphasic pressor response to intravenous norepinephrine bolus infusion.
  • To elucidate the specific roles of alpha-adrenergic receptors and calcium channels in mediating these responses.

Main Methods:

  • Seven healthy volunteers received intravenous bolus infusions of norepinephrine (1, 2, 4 µg/kg).
  • The effects of phentolamine (alpha-blocker), prazosin (selective alpha-1 blocker), and nicardipine (calcium channel blocker) on norepinephrine-induced pressor responses were assessed.

Main Results:

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  • Norepinephrine increased blood pressure dose-dependently and decreased heart rate.
  • A biphasic pressor response (early and late phases) was observed.
  • Phentolamine abolished the pressor response; prazosin inhibited both phases.
  • Nicardipine inhibited only the late pressor response, suggesting involvement of nicardipine-sensitive calcium channels.

Conclusions:

  • Intravenous norepinephrine bolus infusion elicits a biphasic pressor response.
  • The late phase of the pressor response is dependent on vasoconstriction mediated by calcium influx through nicardipine-sensitive calcium channels.