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This Article Full Text Full Text (PDF) All Versions of this Article: 572/3/869    most recent jphysiol.2005.103028v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Fisher, J. P. Articles by White, M. J. Search for Related Content PubMed PubMed Citation Articles by Fisher, J. P. Articles by White, M. J. Related Collections Integrative

¹ School of Sport and Exercise Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
² Department of Integrative Physiology, University of North Texas Health Science Center at Fort Worth, TX 76107, USA
³ Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO 65212, USA
⁴ Copenhagen Muscle Research Center, Department of Anaesthesia, Rigshospitalet, University of Copenhagen, DK-2100, Copenhagen, Denmark

We sought to examine the importance of the cardiac component of the carotid baroreflex (CBR) in control of blood pressure during isometric exercise. Nine subjects performed 4 min of ischaemic isometric calf exercise at 20% of maximum voluntary contraction. Trials were repeated with ß₁-adrenergic blockade (metoprolol, 0.15 ± 0.003 mg kg^–1) or parasympathetic blockade (glycopyrrolate, 13.6 ± 1.5 µg kg^–1). CBR function was determined using rapid pulses of neck pressure and neck suction from +40 to –80 mmHg, while heart rate (HR), mean arterial pressure (MAP) and changes in stroke volume (SV, Modelflow method) were measured. Metoprolol decreased and glycopyrrolate increased HR and cardiac output both at rest and during exercise (P < 0.05), while resting and exercising blood pressure were unchanged. Glycopyrrolate reduced the maximal gain (G_max) of the CBR-HR function curve (–0.58 ± 0.10 to –0.06 ± 0.01 beats min^–1 mmHg^–1, P < 0.05), but had no effect on the G_max of the CBR-MAP function curve. During isometric exercise the CBR-HR curve was shifted upward and rightward in the metoprolol and no drug conditions, while the control of HR was significantly attenuated with glycopyrrolate (P < 0.05). Regardless of drug administration isometric exercise produced an upward and rightward resetting of the CBR control of MAP with no change in G_max. Thus, despite marked reductions in CBR control of HR following parasympathetic blockade, CBR control of blood pressure was well maintained. These data suggest that alterations in vasomotor tone are the primary mechanism by which the CBR modulates blood pressure during low intensity isometric exercise.

(Received 6 December 2005; accepted after revision 28 February 2006; first published online 2 March 2006)
Corresponding author J. Fisher: School of Sport and Exercise Sciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK. Email: j.p.fisher{at}bham.ac.uk

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