| Alpha-2 adrenergic transmission and human baroreflex regulation. | |
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MedLine Citation:
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PMID: 15037555 Owner: NLM Status: MEDLINE |
Abstract/OtherAbstract:
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We observed earlier that central alpha-2 adrenoceptor stimulation in mice greatly augments parasympathetic tone. To test the effects in humans, we assessed autonomic vasomotor tone and baroreflex regulation in 9 normal young adults on 2 occasions, once with and once without clonidine. We determined heart rate (HR), beat-by-beat blood pressure (BP), and muscle sympathetic nerve activity. HR variability was analyzed in the time and frequency domain. Pharmacological baroreflex slopes were determined using incremental phenylephrine and nitroprusside infusions. Clonidine lowered resting BP (122+/-4/73+/-3 versus 100+/-7/55+/-3 mm Hg, P<0.01), muscle sympathetic nerve activity (18+/-3 versus 4+/-2 bursts/min, P<0.01), and HR (62+/-3 versus 56+/-3 bpm, P<0.05). The baroreflex heart rate curve was reset to much lower HR values and showed no saturation at low HR. HR variability profoundly increased during clonidine plus phenylephrine (total power: 3224+/-843 versus 8943+/-2329 ms2, P<0.05). High-frequency power was 1451+/-520 at baseline and 6720+/-2475 ms2 during baroreceptor loading (P<0.05). The low-frequency/high-frequency ratio decreased (1.94+/-0.41 versus 0.69+/-0.10, P<0.05). In contrast, clonidine reduced resting sympathetic vasomotor tone and shifted the operating point of the sympathetic baroreflex to a flat part of the sympathetic baroreflex curve. The shift decreased the ability of the baroreflex to withdraw sympathetic vasomotor tone during baroreflex loading. These baroreflex changes were associated with a moderate increase in phenylephrine responsiveness. We conclude that alpha-2 adrenoceptor stimulation has a differential effect on baroreflex HR and vasomotor regulation. alpha-2 Adrenoceptor stimulation greatly augments baroreflex-mediated bradycardia, most likely by parasympathetic activation. |
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Authors:
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Jens Tank; Andre Diedrich; Elke Szczech; Friedrich C Luft; Jens Jordan |
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Publication Detail:
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Type: Journal Article; Research Support, Non-U.S. Gov't Date: 2004-03-22 |
Journal Detail:
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Title: Hypertension Volume: 43 ISSN: 1524-4563 ISO Abbreviation: Hypertension Publication Date: 2004 May |
Date Detail:
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Created Date: 2004-05-06 Completed Date: 2004-10-08 Revised Date: 2008-11-21 |
Medline Journal Info:
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Nlm Unique ID: 7906255 Medline TA: Hypertension Country: United States |
Other Details:
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Languages: eng Pagination: 1035-41 Citation Subset: IM |
Affiliation:
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Department of Nephrology and Hypertension, Franz-Volhard-Clinic, Medical Faculty of the Charité and HELIOS Klinikum, Berlin, Germany. |
Export Citation:
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| MeSH Terms | |
Descriptor/Qualifier:
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Action Potentials
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drug effects Adrenergic alpha-Agonists / pharmacology* Adrenergic beta-Antagonists / pharmacology Adult Antihypertensive Agents / pharmacology* Baroreflex / drug effects*, physiology Blood Pressure / drug effects Bradycardia / chemically induced Cardiotonic Agents / pharmacology Clonidine / pharmacology* Cold Temperature / diagnostic use Drug Interactions Heart Rate / drug effects Humans Male Middle Aged Nitroprusside / pharmacology Parasympathetic Nervous System / drug effects*, physiology Peroneal Nerve / drug effects, physiology Phenylephrine / pharmacology Pressoreceptors / drug effects*, physiology Propranolol / pharmacology Receptors, Adrenergic, alpha-2 / agonists*, physiology Stroke Volume / drug effects Sympathetic Nervous System / drug effects, physiology Vasomotor System / drug effects, physiology |
| Chemical | |
Reg. No./Substance:
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0/Adrenergic alpha-Agonists; 0/Adrenergic beta-Antagonists; 0/Antihypertensive Agents; 0/Cardiotonic Agents; 0/Receptors, Adrenergic, alpha-2; 15078-28-1/Nitroprusside; 4205-90-7/Clonidine; 525-66-6/Propranolol; 59-42-7/Phenylephrine |
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine
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