Inhibition of aortic chemoreceptor discharge by pressor response to muscular contraction

We have examined the effect of static contraction of the hindlimb muscles on the discharge of aortic chemoreceptors in chloralose-anesthetized cats. The responses of the chemoreceptors to contraction were dependent on the arterial pressure response to this maneuver. When contraction reflexly evoked a pressor response of at least 20 mmHg, the discharge of 26 chemoreceptors was reduced from control levels by 53% (P less than 0.01). The contraction-induced inhibition of chemoreceptor discharge was prevented by phentolamine, an alpha-adrenergic antagonist that also attenuated the contraction-induced pressor response. In addition, the inhibition evoked by contraction was simulated by injection of phenylephrine and inflation of an aortic balloon, both of which evoked pressor responses. However, when contraction failed to significantly change arterial pressure, the discharge of 20 aortic chemoreceptors was not significantly changed from control levels. We conclude that the reflex pressor response to static contraction inhibits the discharge of aortic chemoreceptors. This inhibition of discharge needs to be considered when interpreting the effects of aortic barodenervation on the cardiovascular responses to exercise.