Clonidine and carotid baroreflex in essential hypertension.
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In man clonidine can exert a pronounced hypotensive effect without potentiating baroreceptor influence on blood pressure, therefore this mechanism does not play a prominent role in the clinical antihypertensive action of the drug.Abstract:
Clonidine is believed to reduce blood pressure by a neural action and animal experiments suggest that this consists in potentiation of baroreflexes. In 16 patients with essential hypertension we studied the effects of alterations in carotid sinus baroreceptor activity (neck chamber technique) on arterial blood pressure (catheter measurements) and heart rate, before and after intravenous administration of 150 microgram and 300 microgram of clonidine. The magnitude of the reflex responses was assessed by the slope of the linear regressions relating applied increase and decrease in tissue pressure at the carotid sinus (and therefore applied decrease and increase in carotid sinus transmural pressure) and resulting changes in mean arterial pressure and R-R interval. Clonidine caused a marked reduction in mean arterial pressure (-26 +/- 3 mm Hg) and a slight but significant reduction in heart rate (-5 +/- 1 b/min). There was no evidence for a potentiation of the baroreceptor influence on blood pressure, although a slight potentiation of the baroreceptor influence on heart rate was observed in few instances. We conclude that in man clonidine can exert a pronounced hypotensive effect without potentiating baroreceptor influence on blood pressure. Therefore this mechanism does not play a prominent role in the clinical antihypertensive action of the drug.read more
Citations
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Journal ArticleDOI
Spontaneous Cardiac Baroreflex in Humans: Comparison With Drug-Induced Responses
TL;DR: The spontaneous barore Flex method provides a reliable, noninvasive assessment of human vagal cardiac baroreflex sensitivity within its physiological operating range.
OtherDOI
Arterial Baroreflexes in Humans
Giuseppe Mancia,Allyn L. Mark +1 more
TL;DR: The sections in this article are: Carotid Sinus Massage, Arterial Baroreceptor Control of Heart Rate, and Modification of Arteria Baroreflexes by Drugs.
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Reflex control of the human cardiovascular system
John T. Shepherd,Giuseppe Mancia +1 more
TL;DR: The surge of knowledge about the autonomic regulation of the human cardiovascular system which commenced in the 1940s was a consequence of many events, including the information gained from animal studies of the various reflexogenic zones which modulate the circulation.
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Modification of arterial baroreflexes by captopril in essential hypertension.
Giuseppe Mancia,Gianfranco Parati,Guido Pomidossi,Guido Grassi,Giovanni Bertinieri,Nunzio Buccino,Alberto U. Ferrari,Luisa Gregorini,L. Rupoli,Alberto Zanchetti +9 more
TL;DR: In eight subjects with untreated essential hypertension, blood pressure was monitored intraarterially and the effects of baroreceptor stimulation or deactivation were assessed, which suggests that this drug may potentiate arterial baroreflexes.
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The antihypertensive mechanism of clonidine in man. Evidence against a generalized reduction of sympathetic activity.
B G Wallin,M Frisk-Holmberg +1 more
TL;DR: It is suggested that the drug influences sympathetic outflow by a combination of central and peripheral effects.
References
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TL;DR: It is concluded that clonidine shares with other sympathomimetic agents the ability to depress the liberation of noradrenaline by an action on α-receptors which may be localized prejunctionally.
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TL;DR: In most animals the infusion of 1 μg/kg 2-(2, 6-dichlorophenylamino)-2-imidazoline-hydrochloride into the verterbral artery reduced the carotid occlusion reflex considerably, probably also via a central mechanism.
Journal Article
Cardiovascular adjustment to somatomotor activation. The elicitation of increments in heart rate, aortic pressure and venomotor tone with the initiation of muscle contraction.
Journal ArticleDOI
The Variable-Pressure Neck-Chamber Method for Studying the Carotid Baroreflex in Man
TL;DR: It is concluded that the variable-pressure neck chamber is a valid method for selectively studying the carotid baroreceptor reflex in man, however, transmission of external pneumatic pressure to theCarotid sinus is imperfect and greater for positive than for negative pressure.