The role of the carotid body chemoreceptors and carotid sinus baroreceptors in the control of cerebral blood vessels

We used extracorporeal perfusion of the reversibly isolated carotid sinus region to determine the effects of specific carotid body (CB) chemoreceptor inhibition on eupneic ventilation (V̇i) in the resting, awake, intact dog. Four female spayed dogs were studied during wakefulness when CB was perfused with 1) normoxic, normocapnic blood; and 2) hyperoxic (>500 mmHg), hypocapnic (∼20 mmHg) blood to maximally inhibit the CB tonic activity. We found that CB perfusion per se (normoxic-normocapnic) had no effect on V̇i. CB inhibition caused marked reductions in V̇i (−60%, range 49–80%) and inspiratory flow rate (−58%, range 44–87%) 24–41 s following the onset of CB perfusion. Thereafter, a partial compensatory response was observed, and a steady state in V̇i was reached after 50–76 s following the onset of CB perfusion. This steady-state tidal volume-mediated hypoventilation (∼31%) coincided with a significant reduction in mean diaphragm electromyogram (−24%) and increase in mean arterial pressure (+12 mmHg), which persisted for 7–25 min until CB perfusion was stopped, despite a substantial increase in CO2 retention (+9 Torr, arterial Pco2) and systemic respiratory acidosis. We interpret these data to mean that CB chemoreceptors contribute more than one-half to the total eupneic drive to breathe in the normoxic, intact, awake animal. We speculate that this CB contribution consists of both the normal tonic sensory input from the CB chemoreceptors to medullary respiratory controllers, as well as a strong modulatory effect on central chemoreceptor responsiveness to CO2.

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Dopaminergic efferent inhibition of carotid body chemoreceptors in chronically hypoxic cats

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1984.247.1.r24 ◽

1984 ◽

Vol 247 (1) ◽

pp. R24-R28 ◽

Cited By ~ 6

Author(s):

S. Lahiri ◽

N. Smatresk ◽

M. Pokorski ◽

P. Barnard ◽

A. Mokashi ◽

...

Keyword(s):

Dopamine Receptor ◽

Carotid Body ◽

Carotid Sinus ◽

Dopamine Antagonist ◽

Receptor Blockade ◽

Endogenous Dopamine ◽

Efferent Inhibition ◽

O2 Partial Pressure ◽

Haloperidol Treatment ◽

Carotid Body Chemoreceptors

The observations that the dopamine concentration of the carotid body and efferent inhibition of carotid chemoreceptors are increased during chronic hypoxia led to the hypothesis that the inhibition was due to the effect of an increased dopamine release by the activity of carotid sinus nerve (CSN) efferents. The hypothesis was tested by measuring the effect of dopamine receptor blockade on efferent inhibition of carotid chemosensory responses to graded levels of arterial O2 partial pressure in chronically hypoxic and normoxic cats. Chronically hypoxic cats were prepared by exposing the cats to 10% O2 at sea level for 30–34 days. Carotid chemosensory activity was first measured from a slip of an otherwise intact CSN. The measurements were then repeated after sectioning the remaining nerve trunk. The effect of sectioning the CSN provided the measure of efferent inhibition. In each group of cats the effects of sectioning the CSN with and without dopamine receptor blockade by haloperidol were also studied. CSN section augmented the chemosensory responses in the chronically hypoxic cats. Haloperidol, a dopamine antagonist, augmented the responses further, indicating that a part of the endogenous dopamine effect was independent of the CSN efferents. After haloperidol treatment CSN section did not influence the chemosensory responses. This study confirmed that the efferent inhibition significantly increased in the chronically hypoxic cats and demonstrated that haloperidol blocked the efferent inhibition, suggesting that the mechanism of the augmented inhibition is dopaminergic.

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