Intracarotid norepinephrine infusions inhibit ventilation in goats.

Area of Science:

• Physiology
• Neuroscience
• Respiratory Control

Background:

• Plasma norepinephrine increases during exercise, especially under hypoxic conditions.
• The carotid body (CB) plays a crucial role in mediating ventilatory responses to physiological stimuli.
• Understanding norepinephrine's effect on ventilatory control is essential for respiratory physiology.

Purpose of the Study:

• To investigate the carotid body-mediated effects of norepinephrine on ventilatory control in goats.
• To determine the specific receptors involved in norepinephrine-induced ventilatory changes.
• To differentiate the effects of norepinephrine from baroreceptor feedback and blood pressure changes.

Main Methods:

• Infusion of norepinephrine (NE) into the carotid artery of awake goats, both with intact and denervated carotid bodies.
• Measurements of pulmonary ventilation (VI), arterial blood gases, and blood pressure under normoxic and hypoxic conditions.
• Administration of alpha-adrenergic (phenoxybenzamine), beta-adrenergic (propranolol), and D2-dopamine receptor (domperidone) antagonists.

Main Results:

• NE infusion into the CB-intact carotid artery significantly decreased VI and increased PaCO2 in normoxia, but not in hypoxia.
• NE infusion into the CB-denervated carotid artery did not affect VI or PaCO2, despite increasing blood pressure.
• Ventilatory inhibition by NE was blocked by domperidone and partially blocked by phenoxybenzamine, but unaffected by propranolol.

Conclusions:

• Norepinephrine inhibits ventilation in goats through a mechanism involving carotid chemoreceptors.
• This NE-induced ventilatory inhibition is independent of blood pressure changes and baroreceptor reflexes.
• The effect appears to be mediated by both alpha-adrenergic and D2-dopaminergic receptors on the carotid body.