Journal of Applied Physiology, Vol 66, Issue 2 727-731, Copyright © 1989 by American Physiological Society
Evaluation of the mechanism of decreased airway responsiveness in lambs
A. Stecenko, K. McNicol and S. Polk
Department of Pediatrics, University of Florida College of Medicine, Gainesville 32610.
In this study we investigated three possible mechanisms for the decreased
airway responsiveness (AR) found in young lambs. To evaluate aerosol
delivery, 6 adult sheep (9 mo-3 yr old) and 12 lambs (4-8 wk old) were
challenged with aerosol (aH) and intravenous histamine (ivH). Awake animals
were intubated and studied in a plethysmograph, which measured dynamic
compliance (Cdyn), resistance of the lung, and functional residual
capacity. AR to histamine was measured by administration of increasing
concentrations of histamine until a significant change in lung mechanics
occurred or until the maximum dose of histamine was given. In all six adult
sheep, the response to both aH and iVH was a decrease in Cdyn. In two lambs
Cdyn was decreased with both aH and ivH, in five lambs with neither, in
three lambs with aH only, and in two lambs with ivH only. To examine the
role of beta-adrenergic activity in determining AR, six adult sheep and six
lambs received ivH and on a separate day ivH with propranolol pretreatment
(p + ivH). The median effective dose of histamine that caused a reduction
in Cdyn to 65% of normal saline control (ED65Cdyn) for the adult sheep
given ivH was 3.60 (range 0.23-4.85) and 0.70 (range 0.49-8.0)
micrograms.kg-1.min-1 for p + ivH (P = NS). The median ED65Cdyn for the six
lambs was 8.0 micrograms.kg-1.min-1 for both ivH alone and p + ivH. To
evaluate the role of airway smooth muscle (SM), AR to aH was quantitated in
six adult sheep and six lambs, and then an open-lung biopsy was
performed.(ABSTRACT TRUNCATED AT 250 WORDS)
