Autonomic control of heart rate by metabolically sensitive skeletal muscle afferents in humans.
Isolated activation of metabolically sensitive skeletal muscle afferents (muscle metaboreflex) using post-exercise ischaemia (PEI) following handgrip partially maintains exercise-induced increases in arterial blood pressure (BP) and muscle sympathetic nerve activity (SNA), while heart rate (HR) declines towards resting values. Although masking of metaboreflex-mediated increases in cardiac SNA by parasympathetic reactivation during PEI has been suggested, this has not been directly tested in humans. In nine male subjects (23 +/- 5 years) the muscle metaboreflex was activated by PEI following moderate (PEI-M) and high (PEI-H) intensity isometric handgrip performed at 25% and 40% maximum voluntary contraction, under control (no drug), parasympathetic blockade (glycopyrrolate) and beta-adrenergic blockade (metoprolol or propranalol) conditions, while beat-to-beat HR and BP were continuously measured. During control PEI-M, HR was slightly elevated from rest (+3 +/- 2 beats min(-1)); however, this HR elevation was abolished with beta-adrenergic blockade (P < 0.05 vs. control) but augmented with parasympathetic blockade (+8 +/- 2 beats min(-1), P < 0.05 vs. control and beta-adrenergic blockade). The HR elevation during control PEI-H (+9 +/- 3 beats min(-1)) was greater than with PEI-M (P < 0.05), and was also attenuated with beta-adrenergic blockade (+4 +/- 2 beats min(-1), P < 0.05 vs. control), but was unchanged with parasympathetic blockade (+9 +/- 2 beats min(-1), P > 0.05 vs. control). BP was similarly increased from rest during PEI-M and further elevated during PEI-H (P < 0.05) in all conditions. Collectively, these findings suggest that the muscle metaboreflex increases cardiac SNA during PEI in humans; however, it requires a robust muscle metaboreflex activation to offset the influence of cardiac parasympathetic reactivation on heart rate.
School of Sport and Exercise Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK. j.p.fisher@bham.ac.uk
James P
JP
Fisher
Thomas
T
Seifert
Doreen
D
Hartwich
Colin N
CN
Young
Niels H
NH
Secher
Paul J
PJ
Fadel
D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000328:Adult; D017704:Baroreflex; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D015444:Exercise; D006024:Glycopyrrolate / Q000494:pharmacology; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D007511:Ischemia / Q000503:physiopathology; D007537:Isometric Contraction / Q000187:drug effects / Q000502:physiology; D008297:Male; D008790:Metoprolol / Q000494:pharmacology; D018482:Muscle, Skeletal / Q000187:drug effects / Q000294:innervation / Q000502:physiology*; D009475:Neurons, Afferent / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D010275:Parasympathetic Nervous System / Q000187:drug effects / Q000502:physiology*; D011433:Propranolol / Q000494:pharmacology; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000502:physiology*; D055815:Young Adult
D000319:Adrenergic beta-Antagonists; D011433:Propranolol; D008790:Metoprolol; D006024:Glycopyrrolate