title: Yohimbine attenuates baroreflex-mediated bradycardia in humans.
abstract: Alpha-2 adrenoreceptor stimulation profoundly augments baroreflex-mediated bradycardia presumably through parasympathetic activation. We tested the hypothesis that endogenous alpha-2 adrenergic tone mediates a similar response. In 10 healthy men (age: 33+/-3 years; body mass index: 24+/-1.3 kg/m(2)), we determined baroreflex control of heart rate and sympathetic traffic after ingestion of the selective alpha-2 adrenoceptor antagonist yohimbine (20 mg) or placebo. Testing was conducted in a randomized, double-blind, crossover fashion. We measured heart rate, brachial and finger blood pressure, and muscle sympathetic nerve activity. Sympathetic and parasympathetic baroreflex curves were determined using incremental phenylephrine and nitroprusside infusions (0.3, 0.6, 0.9, 1.2, and 1.5 microg/kg per minute). Plasma norepinephrine increased with yohimbine (50+/-38 ng/L; P<0.05) and was unchanged with placebo (2.2+/-7.6 ng/L). Blood pressure increased 13+/-4/8+/-1 mm Hg with yohimbine and 6+/-2/3+/-1 mm Hg with placebo (P<0.01). HR increased 5+/-1 bpm with yohimbine but did not change with placebo (P<0.01). Ninety minutes after drug ingestion, resting muscle sympathetic nerve activity was similar with yohimbine and with placebo. Baroreflex control of heart rate was decreased with yohimbine (6 ms/mm Hg versus 10 ms/mm Hg; P<0.01) and reset to higher blood pressure and heart rate values. In contrast, yohimbine did not alter the sympathetic baroreflex curve. Yohimbine selectively attenuates baroreflex heart rate control in normotensive young men possibly through parasympathetic mechanisms.
authors: Franz Volhard Clinical Research Center, Medical Faculty of the Charité and HELIOS Klinikum, Berlin, Germany.
authors: Jens
authors: J
authors: Tank
authors: Karsten
authors: K
authors: Heusser
authors: André
authors: A
authors: Diedrich
authors: Robert J
authors: RJ
authors: Brychta
authors: Friedrich C
authors: FC
authors: Luft
authors: Jens
authors: J
authors: Jordan
mesh_terms: D058669:Adrenergic alpha-2 Receptor Antagonists; D000328:Adult; D017704:Baroreflex / Q000187:drug effects*; D001794:Blood Pressure / Q000187:drug effects; D001919:Bradycardia / Q000188:drug therapy* / Q000503:physiopathology; D018592:Cross-Over Studies; D004311:Double-Blind Method; D006339:Heart Rate / Q000187:drug effects*; D006801:Humans; D008297:Male; D009638:Norepinephrine / Q000097:blood; D010275:Parasympathetic Nervous System / Q000187:drug effects / Q000503:physiopathology; D012016:Reference Values; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000503:physiopathology; D013997:Time Factors; D015016:Yohimbine / Q000494:pharmacology*
chemical_list: D058669:Adrenergic alpha-2 Receptor Antagonists; D015016:Yohimbine; D009638:Norepinephrine