Alterations in the structure of the elastic laminae of rat
pulmonary arteries in hypoxic hypertension.
Liu, S. Q.
Biomedical Engineering Department Northwestern University,
Evanston, IL 60208-3107
APStracts 3:0375A, 1996.
The effect of hypoxic hypertension on the remodeling process of the
elastic laminae of the rat hilar pulmonary arteries (PA) was studied
by electron microscopy. Rats were exposed to hypoxia (10% O2) for
periods of 0.5, 2, 6, 12, 48, 96, 144, and 240 hours. The average
tensile stress in the PA wall was estimated on the basis of measured
PA blood pressure, lumen radius and wall thickness, i.e., stress =
radius x pressure / thickness. Changes in the structure and volume of
the PA elastic laminae were examined. The PA blood pressure increased
rapidly within the first several hours of exposure to hypoxia, and
reached a stable level within 2 days. The wall thickness increased
during the initial 6 days and then stabilized relatively, whereas the
lumen radius did not change significantly. As a result, the tensile
stress in the PA wall increased initially due to elevated blood
pressure, then decreased after 48 hours due to PA wall thickening,
and returned to the control level after 4 days. In association with
these mechanical changes, the elastic laminae, which appeared
homogeneous under an electron microscope in normal controls, changed
into structures composed of randomly oriented filaments embedded in
edematous contents within the early 2 days of hypoxia. This change
disappeared gradually and the elastic laminae regained their
homogeneous appearance after 4 days. The volume of the PA elastic
laminae increased rapidly within 12 hours of hypoxia, decreased
afterwards, and returned to the control level after 4 days. The
volumetric change of the elastic laminae was consistent in time
-course and correlated in magnitude with the change in the tensile
stress. These early changes in the structure of the elastic laminae
were associated with a transient decrease in the stiffness of the
PAs. In hypoxic rats administrated with nifedipine, no change was
found in the blood pressure, the tensile stress, as well as the
structure and volume of the elastic laminae of the PAs, in spite of
continuous exposure to hypoxia. These results suggested that altered
tensile stress in the PA wall played a critical role in the
initiation and regulation of structural changes in the elastic
laminae, and these changes might contribute to alterations in the
mechanical properties of the PA in hypoxic hypertension.
Received 15 December 1995; accepted in final form 10 July 1996.
APS Manuscript Number A1316-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 21 August 1996