AJP - Lung Cellular and Molecular Physiology, Vol 268, Issue 4 636-L641, Copyright © 1995 by American Physiological Society
Clearance of surfactant protein B from rabbit lungs
T. Ueda, M. Ikegami, M. Henry and A. H. Jobe
Department of Pediatrics, Harbor-University of California, Los Angeles Medical Center, Torrance 90509, USA.
To characterize the metabolism of surfactant protein B (SP-B) in vivo, we
measured the clearance of SP-B from adult rabbit lungs. Purified rabbit
SP-B was radiolabeled with 125I by the Bolton-Hunter method. Trace amounts
of 125I-labeled SP-B mixed with [14C]dipalmitoylphosphatidylcholine (DPPC)
were given intratracheally via a bronchoscope to rabbits 0-16 h before
collection of alveolar washes (AW). Macrophages were recovered from AW, and
lamellar bodies (LB) were isolated from lung tissue by differential
centrifugation. 125I-SP-B was cleared more rapidly from the airspaces and
the total lung (half-life 7 h) than was DPPC (half-life 11 h in the total
lung). There was an approximately threefold accumulation of SP-B relative
to saturated phosphatidylcholine in macrophages at all times. The
proportion of 125I and 14C radioactivities in lamellar bodies was similar
at 2 and 4 h, but there was 14-fold less 125I-SP-B than [14C]DPPC in
lamellar bodies by 16 h. This loss of SP-B from the lamellar body fraction
is consistent with less recycling of SP-B. The results demonstrate
different clearance kinetics of these two components of surfactant and
indicate a significant role of macrophages in the clearance of SP-B.
