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Norepinephrine Accelerates Diaphragm Fatigue In Vitro
Author(s) -
Frye Gregory Scott,
Ferreira Leonardo F.
Publication year - 2013
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.27.1_supplement.942.7
Subject(s) - norepinephrine , medicine , isometric exercise , endocrinology , phenylephrine , chemistry , agonist , diaphragm (acoustics) , adrenergic receptor , adrenergic , blood flow , receptor , blood pressure , physics , loudspeaker , acoustics , dopamine
Sympathetic nervous activity is increased during exercise, chronic diseases, aging, and psychological stress. Muscle sympathetic nerve endings release norepinephrine, which stimulates primarily alpha‐adrenergic receptors, to regulate vascular conductance and blood pressure. However, little is known about norepinephrine effects on skeletal muscle function that are independent of blood flow. To address this issue, we assessed the contractile properties of diaphragm bundles exposed to buffer solution (control; n = 5) norepinephrine (NE, 100 μM; n = 3) for 60 minutes in vitro (i.e., free of blood flow). After the equilibration period, we determined the diaphragm isometric force‐frequency relationship and fatigue characteristics. The relationship between specific force (N/cm 2 ) and stimulus frequency of diaphragm bundles was unchanged by NE. However, NE accelerated fatigue in vitro . Specifically, NE‐treated muscles generated lower forces than control (P< 0.05) from 45 s until the end of the fatigue trial (300 s). The rate of force development and relaxation were also slower in NE‐treated muscles during the fatigue trial. In subsequent studies, we found that the α 1 ‐adrenergic receptor agonist phenylephrine (PE, 100 μM; n = 3) exerted effects nearly identical to those of norepinephrine. Our preliminary studies suggest that norepinephrine accelerates skeletal muscle fatigue through activation of α 1 ‐adrenergic receptors, and these responses are independent of blood flow.