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Regulation of bronchomotor tone in conscious calves
Authors:P. GUSTIN  A. R. DHEM  P. LEKEUX  F. LOMBA  F. J. LANDSER  K. P. VAN DE WOESTIJNE
Affiliation:Centre de Physio-pathologie Animale, Facultéde Médecine Vétérinaire, Universitéde Liège, 45 rue des Vétérinaires, B-1070 Bruxelles, Belgique;*Laboratorium voor Longfunktieonderzoek, Gasthuisberg (K.U.L.), Herestraat, B-3000 Leuven, Belgïe
Abstract:The purpose of this study was to investigate the effects of some a and β sympathomimetic and sympatholytic drugs on respiratory impedance in healthy conscious calves. Ten Friesian calves were investigated in this study. The forced oscillation technique was used to measure the resistance ( R rs) and the reactance ( X rs) of the respiratory system at frequencies ranging from 4 to 26 Hz. Isoprenaline (1 μg/kg i.v.), propranolol (3 μg/kg i.v.), noradrenaline (2 μg/kg i.v.), xylazine (20 μg/kg i.v.) and yohimbine (0.25 mg/kg i.v.) were administered. Isoprenaline induced a significant decrease of R rs. An increase of R rs after administration of propranolol was observed but without any change of the frequency dependence of R rs. A small increase in the resonant frequency was also recorded. A decrease of R rs was recorded after yohimbine injection. Noradrenaline and xylazine administration increased the resistances and the resonant frequency and induced a negative frequency dependence of R rs. These results suggest that (1) the major effects of β adrenergic drugs are on the central airways, (2) the a adrenergic system may play a role on the regulation of bronchomotor tone in calves, (3) the effects of a adrenergic drugs are on both central and peripheral airways and (4) the forced oscillation technique allows the differentiation of calibre changes occurring in small and large airways.
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