title: Caffeine and theophylline attenuate adenosine-induced vasodilation in humans.
abstract: In this study the local vasoactive effects of adenosine were explored in the human forearm. Adenosine (15 micrograms/100 ml forearm/min) infused into the brachial artery (n = 6) increased forearm blood flow by 572% +/- 140%, versus - 0.5% +/- 5.8% during placebo infusion (p less than 0.01). Lower adenosine infusion rates (5 micrograms/100 ml forearm/min, three times) induced forearm blood flow increments to 330% +/- 94%, 339% +/- 67% and 330% +/- 79%, respectively (n = 8). These forearm blood flow responses were reduced (p = 0.02) during concomitant intra-arterial infusion of two doses of caffeine (30 and 90 micrograms/100 ml forearm/min) to 150% +/- 45% and 98% +/- 28%, respectively. Theophylline (30 micrograms/100 ml forearm/min; n = 6) also significantly attenuated the adenosine-induced increase in forearm blood flow. Enprofylline (30 micrograms/100 ml forearm/min), a related xanthine with a low affinity to adenosine receptors in vitro, did not change the response to adenosine. Nonspecific vasodilation by sodium nitroprusside infusion (50 ng/100 ml forearm/min) was not inhibited by caffeine compared with placebo (forearm blood flow responses were 202% +/- 21% versus 216% +/- 40%; n = 6). This study demonstrated that caffeine and theophylline specifically reduce adenosine-induced vasodilation in humans, supporting the existence of functional human vascular adenosine receptors.
authors.affiliation: Department of Medicine, St. Radboud University Hospital, Nijmegen, The Netherlands.
authors.forename: P
authors.initials: P
authors.lastname: Smits
authors.forename: J W
authors.initials: JW
authors.lastname: Lenders
authors.forename: T
authors.initials: T
authors.lastname: Thien
mesh_terms: D000241:Adenosine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D000293:Adolescent; D000328:Adult; D001993:Bronchodilator Agents / Q000097:blood / Q000494:pharmacology; D002110:Caffeine / Q000097:blood / Q000494:pharmacology*; D005260:Female; D005542:Forearm / Q000098:blood supply; D006801:Humans; D007261:Infusions, Intra-Arterial; D008297:Male; D012039:Regional Blood Flow / Q000187:drug effects; D013806:Theophylline / Q000097:blood / Q000494:pharmacology*; D014664:Vasodilation / Q000187:drug effects*; D014970:Xanthines / Q000097:blood / Q000494:pharmacology
chemical_list: D001993:Bronchodilator Agents; D014970:Xanthines; D002110:Caffeine; D013806:Theophylline; C034347:enprofylline; D000241:Adenosine