Carotid chemoreceptor modulation of regional blood flow distribution and vascular conductance during exercise

Abstract

Stimulation of the carotid chemoreceptors (CC) causes increased sympathetic nervous activity. The CC is sensitive to [H+] and norepinephrine, and therefore we hypothesized that the CC may be active during exercise, contributing to the sympathetic restraint of blood flow to working muscle. We examined the effect of transiently inhibiting CC on cardiac output (QT), hind-limb flow (QL), total (ConT) and hindlimb (ConL) conductance and blood pressure (BP) during exercise (2.5 mph, 5% grade) in chronically instrumented dogs. Bolus injections of Dopamine (5–10 μg/kg) or 30 second infusions of hyperoxic lactated Ringers solution (PO2~700mmHg) were administered via a chronically implanted carotid arterial catheter. Within 10 seconds of injection, Dopamine produced a transient (<15 sec) increase in ConT (32%), ConL (49%), QT(11%) and QL(26%), while BP(−16%) was reduced (all data 5 heart-beat change from baseline). Similarly, hyperoxic Ringers resulted in a rapid, transient increase in ConT (13%), ConL (24%), QT(9%) and QL(19%), and reduction in BP(−4%). In constrast, isovolemic control injections of normoxic lactated Ringers elicited no cardiovascular response. Neither Dopamine nor hyperoxic Ringers caused vasodilation at rest. The vasodilatory response to dopamine and hyperoxic Ringers during exercise was virtually abolished with alpha adrenergic blockade, and was absent in animals following carotid body denervation. Our results indicate that the CC are tonically active during exercise, contributing to the sympathetic restraint of exercising muscle blood flow. (Funded by: NHLBI)