Adenosine infusion in patients lacking carotid chemoreceptors elicited hypotension without significant sympatho-excitation, unlike healthy controls who had a 195% increase in sympathetic activity.
Case-Control (n=11)
Does adenosine infusion increase sympathetic nerve activity in patients lacking carotid chemoreceptors compared to healthy controls?
Carotid chemoreceptor activation is essential for the reflex sympathetic excitation that counterbalances the direct vasodilatory effects of adenosine in humans.
The direct vasodilatory and negative chronotropic effects of adenosine in humans are counterbalanced by a reflex increase in sympathetic nerve traffic. A suggested mechanism for this reflex includes peripheral chemoreceptor activation. We, therefore, assessed the contribution of carotid chemoreceptors to sympatho-excitation by adenosine. Muscle sympathetic nerve activity was recorded during adenosine infusion (140 microg.kg(-1).min(-1) for 5 min) in five patients lacking carotid chemoreceptors after bilateral carotid body tumour resection (one male and four female, mean age 51 +/- 11 years) and in six healthy controls (two male and four female, mean age 50 +/- 7 years). Sympathetic responses to sodium nitroprusside injections were assessed to measure baroreceptor-mediated sympathetic activation. In response to adenosine, controls showed no change in blood pressure, an increase in heart rate (+48.2 +/- 13.2%; P<0.003) and an increase in sympathetic nerve activity (+195 +/- 103%; P<0.022). In contrast, patients showed a decrease in blood pressure (-14.6 +/- 4.9/-17.6 +/- 6.0%; P<0.05), an increase in heart rate (+25.3 +/- 8.4%; P<0.032) and no significant change in sympathetic activity. Adenosine-induced hypotension in individual patients elicited less sympathetic activation than equihypotensive sodium nitroprusside injections. In humans lacking carotid chemoreceptors, adenosine infusion elicits hypotension due to the absence of significant sympatho-excitation. Chemoreceptor activation is essential for counterbalancing the direct vasodilation by adenosine. In addition, blunting of the baroreflex sympathetic response to adenosine-induced hypotension may indicate a direct sympatho-inhibitory effect of adenosine.
Timmers et al. (Thu,) conducted a case-control in Bilateral carotid body tumour resection (n=11). Adenosine infusion vs. Healthy controls was evaluated on Change in sympathetic nerve activity. Adenosine infusion in patients lacking carotid chemoreceptors elicited hypotension without significant sympatho-excitation, unlike healthy controls who had a 195% increase in sympathetic activity.