Effects and mechanism of action of terbutaline on diaphragmatic contractility and fatigue
- 1 April 1984
- journal article
- research article
- Published by American Physiological Society in Journal of Applied Physiology
- Vol. 56 (4) , 922-929
- https://doi.org/10.1152/jappl.1984.56.4.922
Abstract
The effects of i.v. administered terbutaline on diaphragmatic force and fatigue during electrical stimulation of the diaphragm was studied in 17 anesthetized dogs. The diaphragm was stimulated indirectly through the phrenic nerves with electrodes placed around the 5th roots and directly with electrodes surgically implanted in the abdominal side of each hemidiaphragm. Transdiaphragmatic pressure (Pdi) during direct or indirect supramaximal 2 s stimulation applied over a freqeuncy range of 10-100 Hz was measured with balloon catheters during tracheal occlusion at functional residual capacity. In 7 dogs the administration of terbutaline (0.5 mg) had no effect on Pdi at any stimulation frequency applied directly or indirectly. The effect of terbutaline (0.5 mg) on diaphragmatic fatigue was then tested in 10 other dogs. Diaphragmatic fatigue was produced by continuous 20 Hz electrical supramaxial stimulation of the phrenic nerves during 30 min. At the end of the fatigue procedure Pdi decreased by 50 .+-. 5 and 30 .+-. 8% of control values at 10 and 100 Hz, respectively, for either direct or indirect stimulation. The decrease in Pdi for low frequencies of stimulation (10 and 20 Hz) lasted 100 .+-. 18 min, whereas it lasted only 40 .+-. 10 min for the high frequencies (50 and 100 Hz). When terbutaline (0.5 mg) was administered after the fatiguing procedure, Pdi increased within 15 min by 20 .+-. 4% at 10 Hz and by 12 .+-. 3% at 100 Hz for either direct or indirect stimulation. The inotropic effect of terbutaline on the fatigued diaphragm was completely abolished by propranolol (1 mg i.v.), a .beta.-receptor antagonist. Terbutaline has no effect on the fresh diaphragm but increases the contractility of the fatigued diaphragm. This inotropic effect is due to a direct action on the diaphragmatic fiber probably mediated via the .beta.-adrenoceptors. This may bear important therapeutic implications in patients [human] who exhibit respiratory muscle fatigue.This publication has 14 references indexed in Scilit:
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