Document Detail

Mechanism of the attenuated cardiac response to beta-adrenergic stimulation in chronic hypoxia.
MedLine Citation:
PMID:  649464     Owner:  NLM     Status:  MEDLINE    
A blunting of the chronotropic and inotropic responses of the heart to beta-adrenergic stimulation occurs following chronic exposure to hypobaric hypoxia. To pursue the mechanism(s) involved, observations were made in six intact, conscious goats at sea level and in another six goats maintained in a decompression chamber at 445 Torr (approximately 4,300m) for 10 days (Pao2 = 43 Torr). No significant group differences in cardiac frequency and various indices of myocardial performance (peak dP/dt, time-to-peak dP/dt, Vmax) were demonstrable either before or after cholinergic blockade with intravenous atropine methyl bromide, 1 mg/kg. Following hemodynamic studies, thoracotomies were performed and full-thickness biopsies were obtained from the free wall of each of the cardiac chambers. Neither monoamine oxidase activity nor norepinephrine level of any region of the heart was altered by chronic hypoxia. However, a twofold increase (P less than 0.001) in catechol O-methyltransferase activity above sea-level values was found in both the atria and ventricles of the hypoxic animals. Thus, the attenuation in cardiac responsiveness to beta-adrenoceptor stimulation in chronic hypoxia appears unrelated to the level of vagal activity, but may be attributable to enhanced enzymatic inactivation of catecholamines.
J T Maher; J C Deniiston; D L Wolfe; A Cymerman
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  Journal of applied physiology: respiratory, environmental and exercise physiology     Volume:  44     ISSN:  0161-7567     ISO Abbreviation:  J Appl Physiol Respir Environ Exerc Physiol     Publication Date:  1978 May 
Date Detail:
Created Date:  1978-07-15     Completed Date:  1978-07-15     Revised Date:  2013-09-26    
Medline Journal Info:
Nlm Unique ID:  7801242     Medline TA:  J Appl Physiol Respir Environ Exerc Physiol     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  647-51     Citation Subset:  IM; S    
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MeSH Terms
Atropine / pharmacology
Catechol O-Methyltransferase / metabolism
Heart Rate / drug effects*
Isoproterenol / pharmacology*
Monoamine Oxidase / metabolism
Myocardial Contraction / drug effects*
Myocardium / metabolism
Norepinephrine / metabolism
Parasympathetic Nervous System / drug effects
Stimulation, Chemical
Reg. No./Substance:
51-41-2/Norepinephrine; 51-55-8/Atropine; 7683-59-2/Isoproterenol; EC Oxidase; EC O-Methyltransferase

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