Journal of Applied Physiology, Vol 59, Issue 1 72-77, Copyright © 1985 by American Physiological Society
Relation of prostanoids to strength of hypoxic vasoconstriction in dogs with lobar atelectasis
R. C. Garrett and H. M. Thomas 3rd
In dogs with acute lobar atelectasis, meclofenamate administration
decreases shunt fraction uniformly and moderately without abolishing the
wide variation of strength of hypoxic vasoconstriction and resultant
variability of shunt fraction (J. Appl. Physiol. 54: 284-289, 1983). To
further assess the role of prostanoids, we measured prostanoid metabolites
as well as shunt fraction and pressor response to alveolar hypoxia. In six
intact anesthetized dogs with acute left lower lobe atelectasis, shunt
fraction during normoxia was measured with SF6. Levels of
6-ketoprostaglandin F1 alpha (6-keto-PGF1 alpha) and thromboxane B2 in
arterial, mixed venous, and left lower lobe venous blood were measured with
the double antibody radioimmunoassay technique. Ten percent O2 was
administered to assess pressor response. Twenty-one percent O2 was
restarted, meclofenamate was administered, and measurements were repeated
30 min later. Atelectasis did not elevate levels of prostanoid metabolites.
6-Keto-PGF1 alpha averaged 88 +/- 65 pg/ml prior to atelectasis and 81 +/-
73 pg/ml after atelectasis (F = 0.7, P = NS). Likewise, thromboxane B2
values were normal. No transpulmonary concentration differences were found.
6-Keto-PGF1 alpha did not correlate with shunt values, which ranged from 14
to 35% (mean 21%). Meclofenamate effectively blocked cyclooxygenase, as
demonstrated by decreases in prostanoid metabolite levels. It seems likely
that in dogs with acute atelectasis prostacyclin localized in the pulmonary
vasculature decreases strength of hypoxic vasoconstriction modestly and
uniformly without raising blood levels of prostacyclin metabolite.
