Epinephrine facilitates neurogenic vasoconstriction in humans

Area of Science:

• Cardiovascular Physiology
• Neuropharmacology
• Human Physiology

Background:

• Previous studies suggest epinephrine may facilitate neural release of norepinephrine (NE).
• Lack of human studies demonstrating the functional significance of epinephrine's action on neurogenic vasoconstriction.

Purpose of the Study:

• To determine if epinephrine facilitates neurogenic vasoconstriction in humans.
• To investigate the role of beta-receptor stimulation in this process.

Main Methods:

• Forearm vasoconstrictor responses to reflex stimulus (lower body negative pressure) and intra-arterial NE were measured before, during, and after epinephrine or isoproterenol infusion.
• Forearm blood flow and intra-arterial pressure were recorded in 23 healthy male volunteers.
• The ratio of vasoconstrictor responses to LBNP/NE served as an index of NE neural release.

Main Results:

• The LBNP/NE response ratio increased during epinephrine and isoproterenol infusions.
• Epinephrine significantly augmented the vasoconstrictor response to LBNP, while the response to NE tended to decrease.
• Isoproterenol did not alter vasoconstrictor responses to LBNP or NE.

Conclusions:

• Epinephrine, but not isoproterenol, is taken up by adrenergic terminals, released during reflex stimulation, and augments NE release.
• These findings provide the first hemodynamic evidence in humans that epinephrine and isoproterenol facilitate neurogenic vasoconstriction.
• The sustained effect of epinephrine suggests neural uptake and subsequent release are key mechanisms.