title: The role of carotid chemoreceptors in the sympathetic activation by adenosine in humans.
abstract: 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.
authors.affiliation: Department of General Internal Medicine, University Medical Center Nijmegen, PO Box 9101, 6500 HB Nijmegen, The Netherlands. H.Timmers@aig.umcn.nl
authors.forename: Henri J L M
authors.initials: HJ
authors.lastname: Timmers
authors.forename: Gerard A
authors.initials: GA
authors.lastname: Rongen
authors.forename: John M
authors.initials: JM
authors.lastname: Karemaker
authors.forename: Wouter
authors.initials: W
authors.lastname: Wieling
authors.forename: Henri A M
authors.initials: HA
authors.lastname: Marres
authors.forename: Jacques W M
authors.initials: JW
authors.lastname: Lenders
mesh_terms: D000241:Adenosine / Q000494:pharmacology*; D000328:Adult; D017704:Baroreflex / Q000187:drug effects / Q000502:physiology; D001794:Blood Pressure / Q000187:drug effects; D002344:Carotid Body / Q000502:physiology*; D002345:Carotid Body Tumor / Q000601:surgery; D002628:Chemoreceptor Cells / Q000502:physiology*; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D008297:Male; D008875:Middle Aged; D009599:Nitroprusside / Q000494:pharmacology; D013564:Sympathetic Nervous System / Q000187:drug effects* / Q000502:physiology; D014665:Vasodilator Agents / Q000494:pharmacology
chemical_list: D014665:Vasodilator Agents; D009599:Nitroprusside; D000241:Adenosine