Journal of Applied Physiology, Vol 67, Issue 3 1256-1264, Copyright © 1989 by American Physiological Society
Effects of antigen on tracheal circulation and smooth muscle in sheep of different ages
S. E. Webber, R. O. Salonen, M. E. Deffebach and J. G. Widdicombe
Department of Physiology, St. George's Hospital Medical School, London, United Kingdom.
The effects of Ascaris suum antigen on tracheal circulation and tracheal
smooth muscle tone were compared in two groups of sheep: the first group
was 1 yr old (14 sheep) and the second 5 yr old (8 sheep). Cranial tracheal
arteries of anesthetized and paralyzed sheep were perfused at constant flow
with monitoring of perfusion pressure. Tracheal smooth muscle tone was
assessed by measuring changes in the external diameter of the cranial
trachea. Close-arterial injection of antigen (1-20 micrograms) in young
sheep produced dose-dependent vasodilation (6.1-15.5% fall in perfusion
pressure) and smooth muscle contraction (0.06-0.28 mm reduction in tracheal
diam). In old sheep, antigen (1-20 micrograms) produced vasoconstriction
(4.1-16.8%) but no smooth muscle response. The smooth muscle contraction in
young sheep was blocked by mepyramine (2 mg/kg iv) suggesting mediation by
release of histamine. The vasodilation in young sheep and the
vasoconstriction in old sheep were reduced by indomethacin (5 mg/kg iv),
and the residual response was further reduced by FPL 55712 (2 mg/kg iv),
suggesting mediation by both cyclooxygenase products and leukotrienes. Thus
antigen given in the tracheal vasculature releases a mixture of
inflammatory mediators. This mixture of mediators or their actions on the
tracheal vasculature and smooth muscle may depend on the age of the sheep.
