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Methacholine-induced bronchoconstriction in rats: Effects of intravenous vs. aerosol delivery

journal contribution
posted on 1997-01-01, 00:00 authored by F Peták, Z Hantos, A Adamicza, T Asztalos, Peter SlyPeter Sly
To determine the predominant site of action of methacholine (MCh) on lung mechanics, two groups of open-chest Sprague-Dawley rats were studied. Five rats were measured during intravenous infusion of MCh (iv group), with doubling of concentrations from 1 to 16 μg · kg-1 · min-1. Seven rats were measured after aerosol administration of MCh with doses doubled from 1 to 16 mg/ml (ae group). Pulmonary input impedance (ZL) between 0.5 and 21 Hz was determined by using a wave-tube technique. A model containing airway resistance (Raw) and inertance (Iaw) and parenchymal damping (G) and elastance (H) was fitted to the ZL spectra. In the iv group, MCh induced dose-dependent increases in Raw [peak response 270 ± 9 (SE) % of the control level; P < 0.05] and in G (340 ± 150%; P < 0.05), with no increase in Iaw (30 ± 59%) or H (111 ± 9%). In the ae group, the dose-dependent increases in Raw (191 ± 14%; P < 0.05) and G (385 ± 35%; P < 0.05) were associated with a significant increase in H (202 ± 8%; P < 0.05). Measurements with different resident gases [air vs. neon-oxygen mixture as suggested (K. R. Lutchen, Z. Hantos, F. Petak, A. Adamicza, and B. Suki. J. Appl. Physiol. 80: 1841-1849, 1996)] in the control and constricted states in another group of rats suggested that the entire increase seen in G during the iv challenge was due to ventilation inhomogeneity, whereas the ae challenge might also have involved real tissue contractions via selective stimulation of the muscarinic receptors.



Journal of Applied Physiology






1479 - 1487