close

Вход

Забыли?

вход по аккаунту

?

The postnatal growth of the rat lung II. Autoradiography

код для вставкиСкачать
The Postnatal Growth of the Rat Lung
11. AUTORADIOGRAPHY '
SHIRLEY L. KAUFFMAN,a PETER H. BURR13 AND
EWALD R. WEIBEL3
a Department of Pathology, State University of New York, Downstate
Medical Center, Brooklyn, New York and Department of Anatomy,
University of Berne, Berne, Switzerland
ABSTRACT
Combined morphometric and autoradiographic methods were
used to analyze the postnatal growth of rat lung from 1-21 days after birth.
Each cell population had distinct growth patterns with an increase in the number of fibroblasts and capillary endothelial cells largely determining the increase
in interstitial volume and capillary surface, respectively. The height of proliferation activity in mesodermally-derived cells was concurrent with the outgrowth of
secondary alveolar septa (between days 4 and 13). Analysis of the location of
labeled cells on day 7 showed that the higher labeling index on septal crests
could be ascribed to the proliferative activity of fibroblasts and endothelial cells.
Within the alveolar epithelium only the type I1 alveolar cells had a detectable
labeling index. Over the first week, the number of type I epithelial cells steadily
increased while the number of type I1 cells remained constant. Subsequently the
number of type I1 cells increased rapidly, reached a peak on day 13 and then
decreased, whereas type I cells continued to increase in number. These facts led
us to consider that type I1 epithelial cells may represent the stem cell population of alveolar epithelium. The height of proliferative activity of type I1 cells
on day 7 coincided with the outgrowth of septal crests and was followed by the
steepest increase in number of type I and I1 cells.
Between the 10th and 21st day labeling indices rapidly declined, cell production became undetectable after day 13.Increase in alveolar and capillary surface
area however continued, resulting in a thinning of the interstitial layer and of
the epithelial and endothelial sheets.
The lung of the newborn rat is an immature organ which undergoes major postnatal morphogenetic changes during the
first 21 days of life. Expansion of the air
spaces, formation of the alveolar septa,
thinning of the interstitium and remodeling of the capillary network, all act to
transform the gas exchange apparatus
from its late fetal to near mature form
within these 3 weeks (Burri, '74).
Although no previous studies have been
specifically directed toward examination
of the kinetics of the various cell populations involved in these changes, some data
have been obtained which indicate a decline in 3H-thymidine labeling index in
fetal rat lung as a whole between the 17th
and 19th day of gestation and birth (Kury
et al., '67) followed by a postnatal peak of
cell proliferation (Crocker et al., '70;
ANAT. REC..180: 63-76.
OHare and Townes '70). The present autoradiographic investigation was directed
towards evaluation of the cell kinetics of
the populations involved in the growth and
morphogenesis of the rat lung, and a correlation of this with the morphometric
data described in the first paper of this
series was attempted.
MATERIALS AND METHODS
A. Tissue preparation
CFN-COBS strain rats ( 3 animals per
group) were injected with 3H-thymidine,
1 pc/gram body weight (3.0 Ci/mM,
New England Nuclear) at the following
ages: 24 hours, 4, 7, 10, 13, 21 days. From
Oct. 2. '73. Acceuted Feb. .5, '74.
study was supported by grants from the Council for Tobacco Research U S A . and from the Swiss
National Science Foundation 3.5.68 and 3.682.71.
Received
-.
1 This
63
64
S. L. KAUFFMAN, P. H. BURR1 A N D E. R. WEIBEL
day 4 onwards the injections were made
at the same daily hours, from 8 to 12 AM,
following a strict time-table to avoid possible diurnal variations in cell division
rates. These animals were part of the same
population of rats as that used for the
morphometric study reported i n the companion paper (Burri et al., '74); they were
fixed simultaneously.
Thirty-five minutes after 3H-thymidine
injection, the rats were anesthetized with
HypnormR, the dosage being 0.2 m1/100
gram body eight.^ Following a tracheostomy, a bilateral pneumothorax was induced through the diaphragm via a n
abdominal incision and the lungs immediately instilled with buffered osmium tetroxide through a tracheal cannula, under
a constant instillation pressure of 20 cm
of water (Burri and Weibel, '71). Instillations were done between 50 and 55 minutes after 'H-thymidine injection. The
lungs were removed and fixed in toto for
2 hours i n the same solution. The lungs
were dissected from the mediastinal contents and the lung volume determined by
saline displacement. Multiple 1 m m slices
were then made of the lungs and these
were sectioned into 1 m m cubes.
Ten sample blocks of each animal were
embedded in Epon; of these, 4 blocks were
cut with glass knives to produce 1.5 E".
sections. Blocks were trimmed between sections to obtain 4 well spaced sections of
each block. These were mounted on glass
slides, dipped in NTBz emulsion and exposed in light proof boxes at 4°C for 30
days. After development in Dektol, the
slides were stained with a n alkaline solution of toluidine blue.
B.
Autoradiography
1. Analysis of autoradiographs
Autoradiographs were examined with a
Leitz microscope fitted with a n eye piece
enclosing a test area of 7225
The identity and the number of cells and the proportion of nuclei labeled for each cell type
were determined in 60 test areas from each
animal using the following criteria.
Fibroblasts were identified by their location in the interstitium and their stellate
intracytoplasmic lipid droplets (figs. 1-4).
Capillary endothelial nuclei (fig. 3 ) were
identified by their location, shape and attenuated cytoplasm adjacent to the nucleus, which helped to distinguish them
from the more numerous intravascular
mononuclear cells. Type I1 alveolar cells
(figs. 1, 3 , 4 ) were identified by the combined occurrence of several of the following characteristics : location either on the
alveolar surface or in the interstitium,
presence of strongly osmiophilic, round
cytoplasmic (lamellar) bodies and a fuzzy
surface due to microvilli. The type I alveolar cell (figs. 3 , 4) was distinguished from
the type I1 cell by its elongated nucleus
and slim cytoplasm free of lamellar bodies,
and from the capillary endothelial cell by
its location.
I n this context it must be stressed that,
although the criteria worked out to differentiate the septal cells cannot be easily
demonstrated i n micrographs, it does not
cause too much difficulty for a n experienced investigator to identify the various
cell types in the microscope. Furthermore,
electron microscopic investigations confirmed the correctness of the criteria
worked out above.
2.
Labeling indices
The 3H-thymidine labeling index (percent of nuclei in the DNA synthetic period)
was obtained by counting a minimum of
1000 fibroblast and endothelial nuclei, and
500 type I1 nuclei from each animal, and
recording the total number and the number
labeled. A nucleus covered by 4 or more
grains was considered labeled; the background was less than 2 grains per test area.
3.
Location of labeled cells
To determine whether labeled cells
showed a preferential location on air space
surface during the formation of secondary
septa, the contours of air spaces were
scanned; the identity of each cell encountered and its location was charted on graph
paper. Cells were further characterized as
either labeled or unlabeled and a s being
either on primitive septa or on septal buds.
In each of the three 7 days old animals
four samples of about 500 cells each, i.e.
over 2000 cells per animal were examined.
The labeling index on septal buds, both
4 1 ml of HypnormR contains 0.2 mg Fentanyl and
10 mg Fluanison.
AUTORADIOGRAPHY OF POSTNATAL LUNG GROWTH
65
Fig. 1 Telophase in type I1 alveolar epithelium (Tz);each cell contains large lamellar
bodies. Notice large fibroblasts ( F ) with intracellular lipid. This and following photographs
were taken of autoradiograms made from 1.5 p plastic section. Toluidine blue; oil immersion x 900.
total and by cell type was compared with
the overall labeling index.
C. The total number of nuclei
The number of nuclei per cm3 of lung
tissue (numerical density, Nv) was calculated for each animal using the relation
- Nv = NA/D, where Nv is the number of
nuclei per unit volume, RAthe number of
nuclei per unit section area, and
is the
mean nuclear caliper diameter (DeHoff
and Rhines, '61 ).
The mean caliper diameter of nuclei,
is shape dependent and therefore varies between the cell types. For type I1 epithelial
cells we assumed a spherical shape. In this
case we calculated the true mean nuclear
diameter b from the mean apparent diam-
n,
66
S.
L. KAUFFMAN, P. H. BURR1 AND E. R. WEIBEL
Fig. 2 Septal bud containing labeled fibroblast (LF) adjacent to unlabeled fibroblast (F),
both containing intracytoplasmic lipid.
(a)
eter
of 100 nuclear profiles by the
basic relationship :
D=-d.
-
4
i7
For shape of the fibroblast nuclei we assumed a prolate ellipsoid. Measurement of
axial ratios of profiles revealed that the
long axis was 1.8-2.0 times the small
diameter. D was then calculated from the
measurement of mean random chord
length E on 100 profiles; using the geo-
metric formulae given by Hilliard ('67)
we estimated that
1.7 X
For endothelial and type I epithelial cells we proceeded similarly.
The number of nuclei ( N ) of each cell
type in the whole lung was calculated by
multiplying the numerical density by the
volume of lung parenchyma (i.e. the gas
exchanging parts of the lung) estimated
by light microscopic morphometry (Burri
et al., '74).
a=
r.
AUTORADIOGRAPHY OF POSTNATAL LUNG GROWTH
67
Fig. 3 Base of septal bud with labeled endothelial cell (LE), type I alveolar cell (Ti),
type I1 (Tz)and fibroblast ( F ) also shown.
D.
Estimation of tissue volume
The parenchymal volume of the lungs
and the volume of epithelium, endothelium
and interstitiurn were estimated by light
and electron microscopic morphometry
respectively on the animals used in a companion paper (Burn et al., '74). They were
different animals, but were derived from
the same population, and their lungs were
fixed by instillation of glutaraldehyde instead of osmium tetroxide.
to 13.25 X 10' on day 13 and then decreased si@ficantb to 8.9 lo' On day
21. The total number of fibroblasts
(Nf = Nvf lung Parenchymal
(fig. 5b) increased from 4.3 X 10' at 24
hours to 17.5 x 10' on the 13th day and
then declined to 14.4 X 10' on the 21st
day. The SH-labeling of fibroblasts (LIr)
was 6.8% at 24 hours (fig. sa), increased
and
to a maximum of 14.2% on day
then fell to less than 1% on day 13. No
labeled fibroblasts were found on day 21.
RESULTS
Capillary endothelium
The numerical density of endothelial
nuclei (N",,,) was relatively constant, approximately 11-12 x 10' nuclei per cm'
between days 1 and 10. Between days 10
and 13, there was a significant decrease in
Nvento 8.1 X lo7 on day 13 and 7.1 X lo'
on day 21.
A.
Proliferation pattern of t h e
various cell types
1. Fibroblasts
The numerical density of fibroblast nuclei (Nw) increased significantly over the
growth period from 10.05 X lo' on day 1
2.
68
S.
L. KAUFFMAN, P. H. BURR1 AND E. R. WEIBEL
Fig. 4 Intravascular mitosis in septa1 bud (SB). Fibroblast ( F ) , type I1 (Tz) and type
I (TI)alveolar epithelium are shown.
The number of capillary endothelial
cells (Nen;fig. 6b) in 24 hours rat lung
was approximately equal to the number of
fibroblasts (4.97 X lo7); the subsequent
numerical increase was less, reaching
13.5 X 10‘ on the 10th day and then declining. The labeling index ( L L ) varied
between 8 and 10% over the first 10 days
and then fell rapidly between days 10 and
13 (fig. 6a). Labeled endothelial cells were
not found on the 21st day.
3.
Epithelium
The numerical density of alveolar epithelial nuclei ( N Y e p I + I f ) decreased significantly from 4.3 X lo7to 2.6 X lo7between
days 1 and 4. Numerical density of both
type I and I1 decreased, but the largest
AUTORADIOGRAPHY OF POSTNATAL LUNG GROWTH
69
FIBROBLASTS AND INTERSTITIUM
L'f
I
1 3----.J----j
.20
/
.16
i
\
\
I
"I
I: 24-
2
k
&
.20-
(1:
W
c
-
.16-
LL
0
.12r
3 .080
>
AGE IN DAYS
Fig. 5 a. Labeling index of fibroblast (LIf) and total number of labeled fibroblasts
(NIE)in pulmonary parenchymal interstitium.
b. Total number of fibroblasts (Nr) and morphometrically determined absolute volume
of interstitium (Vi.) (Burri et al., '74). For both figures values are means and brackets
include k 1 standard error.
70
S. L. KAUFFMAN, P. H. BURR1 AND E. R. WEIBEL
EN DOT HELIUM
hen
106
2
/T
/
/
+, ---d
//
z
OO
'\\
71
\
//
B5
YNI,"
\
\
m
6:
\
\
\
2
6 %
\
r
0
m
* v)
F
0-,
.
a
J en
~ e l l sc
cm3 m*
,107
I4
3i
.12--.24
/
W
I
l0
n
z
/
.10 .-.a3
//
/
/
1
-I
\<Nen
\
\.I
__--_
-------e
/
SCV."
/
./A
1
12
0
I-
z
'O
0
71
89
U
s
6 1
m
!-
4 O
P
r
v)
2
b
Fig. 6 a. Labeling index of pulmonary capillary endothelium (Lien) and total number
of labeled endothelial cells (NI~,,).
b. Total number of endothelial cells (N.") and absolute volume of endothelium of pulmonary capillaries (Ve,,).Additionally absolute capillary surface area ( S c ) is shown. (Morphometric results from Burri et al. '74.) For both figures values are means and brackets
include -C 1 standard error.
71
AUTORADIOGRAPHY OF POSTNATAL LUNG GROWTH
component of this decrease was due to the
type I1 alveolar epithelial cells.
The total number of type I1 alveolar
cells (NepI,) remained constant between
days 1 and 7, and then increased rapidly
from 13 X lo6 to 28 X 10' between day 7
and day 13 (fig. 7b).
The number of type I alveolar cells
(NepI ) increased more or less steadily over
the entire period, from 4.3 X lo6 on day
1 to 12.8 X 10' on day 21 (fig. 7b), with
only a slight acceleration between days 7
and 10.
The proportion of labeled type I1 cells
(LLP,,) increased from 0.45% to over
6.0% in the first week, and declined after
the 10th day (fig. 7a). No labeled type I
cells were found in any of the preparations
(fig. 7a), although a total of approximately
two thousands was screened over the
course of the various tissue analyses.
7-12 (120 hours). Type I alveolar cell
population doubled between days 1 and 9,
although no labeled cells were found.
Labeling of cells on
septal buds
The question arises whether the labeled
cells are evenly dispersed throughout the
lung, or whether they occur with greater
frequency on those parts of tissue which
are in the process of forming interalveolar
septa. We have therefore separately recorded the number of labeled cells on the
so-called septal buds and on other parts of
the air space wall.
Lungs of 7 days old animals were
chosen for this analysis because morphometric and electron microscopic studies
showed this point corresponded to the most
intense phase of septal outgrowth. Results
of comparison of overall labeling index
with labeling index of nuclei on septal buds
B. Population doubling times
are shown in table 1.
Over the first 13 days, the population of
I n 10 out of the twelve samples investifibroblasts increased by a factor of 4. The gated the ratio of the labeling index on
first population doubling occurred between buds to the overall labeling index was
days 1 and 6.2 (doubling time 126 hours) larger than 1, with a n average of 1.4. The
and the second between 6.2 and 13 days 95% confidence interval being 0.18 it is
(162 hours). This increase in doubling evident that the labeling index was sigtime can be related to the decline in the nificantly higher on septal buds than in
fraction of labeled cells which began the parenchyma as a whole. Analysis of these
4th day. Capillary endothelial cells in- data with respect to the various cell types
creased by a factor of 3 between days 1 present in the septa, indicated that both
and 10; the initial population doubled be- endothelial cells and fibroblasts were retween days 1 and 8 (168 hours). The type sponsible for the higher labeling indices
I1 alveolar cell population showed no nu- on crests, whereas labeled type I1 epithelial
merical change until after the 7th day, and cells were evenly distributed over primitive
then the population doubled between days septa and crests.
C.
TABLE 1
Comparison of overall septal labeling index w i t h labeling index on septal buds on day 7
Animal
A
B
C
Sample
LI
on septal buds (A)
1
2
3
4
1
2
3
4
1
2
3
4
Overall mean, 1.396; S.E.,
0.130
0.131
0.160
0.185
0.057
0.071
0.107
0.087
0.088
0.146
0.096
0.097
LI
on whole septal wall (B)
0.074
0.090
0.110
0.101
0.061
0.072
0.071
0.073
0.054
0.096
0.075
0.081
0.082; 95% confidence interval, f 0.180.
A
Ratio B
1.757
1.456
1.455
1.832
0.934
0.986
1.507
1.192
1.630
1.521
1.280
1.198
mean
1 S.E.
1.625
20.114
1.155
20.15
1.407
e0.117
72
S.
L. KAUFFMAN, P. H. BURR1 AND E. R. WEIBEL
DISCUSSION
The combined analysis of autoradiographic and morphometric data from neonatal rat lungs suggests that the early
postnatal growth period can be divided
into 3 phases:
Days 1-4: Mobilization of proliferative
cells characterized by a high or rapidly increasing labeling index, an enlargement of
the air space volume by 8 7 % , and only
moderate tissue volume increase;
Days 4-13: Period of intense cell production and outgrowth of secondary alveolar septa characterized by differential cell
proliferation on septa1 buds and concomitant increase in alveolar and capillary surface area;
Days 13-21: Period of differentiation
with rapid decline in labeling index and
cell production, and continued increase in
alveolar and capillary surface area, resulting in a thinning of interstitium and mean
barrier thickness.
This period in which growth and maturation are concurrent, represents the beginning of the phase of equilibrated lung
growth (Burri et al., '74).
One feature of neonatal lung growth
brought out in this study was the distinctly
different proliferative pattern of the 3 main
cell populations, as illustrated by their
labeling indices (fig. 8). Fibroblast labeling index reached its peak on day 4.
Despite the following rapid decline it remained relatively high (over 7% ) during
the period of formation of secondary septa
(days 4-10). Its decline was folIowed by
an actual reduction in total cell number
on day 21. Endothelial labeling index was
high already at 24 hours and remained
at the same level until day 10. There was
a marked increase in the total number of
endothelial cells and in the number of
labeled cells after day 7, which was related to the proliferation of new capillaries
in the forming secondary septa. The labeling index of type I1 alveolar epithelial cells
was low at birth and slowly rose to its peak
on day 7, while type I cells showed no
labeling at all. These patterns of cell production are related to those of growth in
cell number and in volume of the various
tissue components.
Growth of the fibroblast population (Nf)
was directly related to the pattern of
change in the interstitial volume (Vi,,),
as shown in figure 5b. Both curves rose to
a peak on day 13, followed by a decline
towards day 21.
Whilst the highest number of capillary
endothelial nuclei could be counted on day
10, the endothelial cell volume increased
up to day 13 and leveled off until day 21.
The capillary surface area, however, followed the volume increase until day 13,
but then continued to increase steadily
(fig. 6b). This difference between changes
in cell number and volume on the one
hand and surface growth on the other
hand can be explained by a spreading out
and thinning of the endothelial cytoplasm,
as revealed by a decrease in the mean
barrier thickness of endothelium (Burri
et al., '74).
The number of type I epithelial cells
(NepI ) increased slowly from day 1 to 7
and from day 10 to 21 respectively. Its
faster increase between days 7 and 10,
occurred simultaneously with the steepest
augmentation in the number of type I1
cells (NepII;
fig. 7b). The period of days
13-21 showed the largest discrepancy between Sa and Vep on the one hand and
N.,I on the other; this reflected the reduction of epithelial mean thickness,
which was due to spreading out and thinning of the type I cytoplasmic processes.
The changes in the number of type I1
cells (NepII)showed an independent pattern (fig. 7b). Particularly, they could not
be related to either of the morphometric
parameters V,, or S,. There are two reasons which could explain this devious proliferation pattern. On the one hand, the
type I1 cell must be considered the secretory cell of the alveolar epithelium (Buckingham et al., '66; Weibel, '73; Gil and
Reiss, '73); it is therefore not directly related to the formation of a large and thin
Fig. 7 a. Labeling index of alveolar epithelium (LIep11) and total number of labeled epithelial cells (NleP11). Notice that only type I1 alveolar
cells were labeled (LIepII and NlepI I ) , all the
values for type I cells being 0.
b. Number of type I (NepI ) and type I1 cells
(NepI I ) , total cell number in alveolar epithelium
(N, I and N, II), and absolute volume of alveolar epithelium (Vep), The absolute alveolar surface area (Sa) is also deyicted. (Morphometric
results from Burri et al., 74). For both figures
all the values represent group means and the
brackets include -r- 1 standard error.
73
AUTORADIOGRAPHY OF POSTNATAL LUNG GROWTH
Llep
EPITHELIUM
I
Jlep
105
1
14
I2
z
0
71
\
A
/
:j
W
0
10
\
/
pl
%
'
*?J
4
I
.12
2
;;
6
0
rn
r
I-
.08
4 w
1
2
I
. 004 L
a
'
1
vep Sa
JeP
0 3 m2
P.
7'
/
/
/
-.
NepI+Nepl[
---/-
.-.
-0
/
106
35
2
-i
30
z
25
m
73
!O 7
I
15
P
P
r
10
5
I ,
1
b
4
7
10
13
AGE IN DAYS
Figure 7
21
74
S. L. KAUFFMAN, P. H. BURR1 AND E. R. WEIBEL
AGE IN DAYS
Fig. 8 For comparison the labeling indices of the various cell types in the parenchymal
portion of the growing rat lung are shown in one graph. Each cell type displays its own
pattern (see text): fibroblasts (f), endothelial cells ( e n ) and alveolar epithelial cells of
type I1 (ep 11). For endothelium and fibroblasts no labeling could be detected on day 21.
air-blood barrier, the main event of this
growth period ( B d et al., '74; Burri, '74).
On the other hand, this study suggests
that the type I1 cell might represent the
stem cell of the type I epithelial cell, because it showed that type I cells increased
in number without the occurrence of any
3H-thymidinelabeling (DNA synthesis) in
the nuclei of this cell type.
Several independent observations related
to the repair of damaged alveolar epithelium support our hypothesis. Firstly, in
oxygen poisoning the squamous processes
of type I alveolar epithelial ceIls become
damaged and a repair ensues in the form
of a lining of cuboidal cells, which have
all the characteristics of type I1 cells; these
cells are subsequently transformed into
squamous type I cells (Kapanci et al., '69;
Bowden and Adamson, '71; Gould et al.,
'72). Recently it could be shown that this
is a characteristic pattern of alveolar
epithelial repair, irrespective of the type
of damage (Carrington and Green, '70;
Bachofen and Weibel, '74). Secondly,
Evans et al. ('73) have recently demonstrated in an autoradiographic study on
tissue repair after NOz-damage, that only
type I1 cells entered the division cycle by
synthesising DNA, whereas type I cells
did not; they also showed that labeled type
I cells could be found within 48 hours presumably arising from labeled type I1 cells.
The reason for the inability of type I cells
to divide probably lies in their unusually
high level of topological differentiation in
that each cell forms multiple apical cytoplasmic plates (Weibel, '71, '74), a configuration which would make cytoplasmic division difficult. Our observations suggest that
the alveolar epithelial cells of the growing
lung proliferate in a very similar fashion to
the adult epithelium during repair. OHare
and Townes ('70) however found a relatively high incidence of labeled type I cells
in newborn rats in a marker dilution study
and in a daily label index study. In the
marker dilution study postnatal labeling of
AUTORADIOGRAPHY OF POSTNATAL LUNG GROWTH
type I cells was obtained by injecting the
mother with 3H-thymidine on the 16th day
of gestation. Whereas the labeled type I
cells found in this case could well have
been derived from type I1 precursor cells,
the results of the daily label index study,
with labeling indices as high as 7% on
the k s t and 13% on the third postnatal
day are very much in contradiction with
our present findings, This problem certainly needs further investigation, as it
also remains to be proven whether in the
growing lung newly divided type I1 cells
can transform into type I cells.
Another interesting observation with respect to alveolar epithelium deserves to be
discussed in this context. The numerical
density of type I1 nuclei was greatest at 24
hours and decreased by nearly 50% within
4 days. However, over this period of lung
expansion the total number of type I1 cells
remained constant. Several investigators
(Short, '50; Woodside and Dalton, '58;
Klika, '65) have described desquamation
of type I1 alveolar cells in the neonatal
lung and ascribed morphogenetic changes
to this event. Loosli and Baker ('62) however, found no evidence of epithelial desquamation in newborn lung and believed
the apparent decrease in epithelial nuclei
was due to a flattening of alveolar lining
cells. It seems unlikely from the present
study that type I1 cells desquamated, because, in the presence of the low labeling
index, desquamation of type I1 cells would
have resulted in a decline in the number
of cells, whereas the number remained
constant. We must therefore conclude, that
the reduction in numerical density of these
cells is due essentially to an enlargement
of the containing space rather than to a
loss of cells.
The most important morphogenetic
event of the growth period investigated
was the neoformation and outgrowth of
secondary alveolar septa, which was accompanied by considerable transformations in the tissue (Burri, '74). We were
led to ask whether the proliferating cells
were randomly distributed throughout the
tissue, or whether they showed a certain
concentration in the region of the forming
secondary septa. We therefore determined
the labeling indices of the cells located in
and at the base of septal crests at day 7
75
and found that the septal crests had a sigscantly higher labeling index than the
tissue as a whole. This finding suggests
that the formation of secondary septa is
associated with differential proliferation,
and is not simply due to cell migration or
purely mechanical factors as postulated by
Short ('50). Furthermore it appeared that
the labeled type I1 cells were not preferentially located on crests, as was the case
for both endothelium and fibroblasts. The
growth of alveolar epithelium had hence
once more a pattern different from that of
cells of mesodermal origin.
ACKNOWLEDGMENTS
The authors wish to acknowledge the
excellent technical assistance of Mr.
Hiroshi Ozaki, Ms. Wally Wehle and
Ms. Krishna Anand. The charts were
drawn by Ms. Elizabeth Cuzzort and Mr.
Karl Babl; the photomicrographs were
made by Mr. Willy Kratil.
LITERATURE CITED
Bachofen, M., and E. R. Weibel 1974 Basic
pattern of tissue repair in human lungs following unspecific injury. Chest, 65: 14s-19s.
Bowden, D. H., and I. Y. R. Adamson 1971
Reparative change following pulmonary cell
injury. Ultrastructural, cytodynamic and surfactant studies in mice after oxygen exposure.
Arch. Path. 92: 279.
Buckingham, S., H.0. Heinemann, S. C. Sommers
and W. F. McNary 1966 Phopholipid synthesis in the large pulmonary alveolar cells.
Am. J. Pathol., 48: 1027-1041.
Burri, P. H. 1974 The postnatal growth of the
rat lung. 111. Morphology. Anat. Rec., 180: 7798.
Burri, P. H., J. Dbaly and E. R. Weibel 1974
The postnatal growth of the rat lung. Part 1.
Morphometry. Anat. Rec., 178: 711-730.
Burri, P. H., and E. R. Weibel 1971 Morphometric estimation of pulmonary diffusion
capacity. 11. Effect of Poz o n the growing lung.
Adaptation of the growing rat lung to hypoxia
and hyperoxia. Respir. Physiol., I 1 : 247-264.
Carrington, Ch. B., and T. J. Green 1970 Granular pneumocytes in early repair of diffise
alveolar injury. Arch. Intern. Med., 126: 464465.
Crocker, T. T., A Teeter and B. Nielson 1970
Postnatal cellular proliferation in mouse and
hamster lung. Cancer Res., 30: 357-361.
DeHoff, R. T., and F. N. Rhines 1961 Determination of number of particles per unit volume from measurements made on random
plane sections: The general cylinder and the
ellipsoid. Trans. AIME, 221: 975-982.
76
S. L. KAUFFMAN, P. H. BURR1 AND E.
Evans, M. J., L. J. Cabral, R. J. Stephens and
G. Freeman 1973 Renewal of alveolar epithelium in the r a t following exposure to NOS.
h e r . J. Path., 70: 175-198.
Gil, J., and 0. K. Reiss 1973 Isolation and
characterization of lamellar bodies and tubular myelin from rat lung homogenates. J. Cell
Biol., 58: 152-171.
Gould, V. E., R. Tosco, R. F. Wheelis, N. S. Gould
and Y. Kapanci 1972 Oxygen pneumonitis
in man. Ultrastructural observations on the
development of alveolar lesions. Lab. Invest.,
26: 499-508.
HiIliard, J. E. 1967 The calculation of the
mean caliper diameter of a body for use in the
analysis of the number of particles per unit
volume in stereology. Proc. 2nd Internat.
Congress for Stereology, Chicago. New York,
Springer-Verlag, pp. 211-215.
Kapanci, Y., E. R. Weibel and H. P. Kaplan
1969 Pathogenesis and reversibility of the
pulmonary lesions of oxygen toxicity in monkeys. 11. Ultrastructural and morphometric
studies. Lab. Invest., 20: 101-118.
Klika, E. 1965 The electron microscopy and
histochemistry of the lung alveolus. Acta Univ.
Carol. Med. Monograph 20.
R. WEIBEL
Kury, G., J. M.Craig and H. W. Carter 1967
Autoradiography of rat lung before and after
birth. Nature, 213: 619-621.
LOOSE,C. G.,and R. F. Baker 1962 The human
lung: microscopic structure and diffusion. In:
Ciba Symposium on Pulmonary Structure and
Function. A. V. S. de Reuck and M. O’Connor,
eds. Little Brown & Co., Boston, pp. 194-204.
O’Hare, K. H., and P. L. Townes 1970 Morphogenesis of albino rat lung: a n autoradiographic
analysis of the embryological origin of the
type I and I1 pulmonary epithelial cells.
J. Morph., 132: 69-88.
Short, R. H. D. 1950 Alveolar epithelium in
relation to growth of the lung. Phil. Trans.
Roy. SOC. ( B ) , London, 235: 35-86.
Weibel, E. R. 1971 The mystery of “nonnucleated plates” in the alveolar epithelium of
the lung explained. Acta anat., 78: 425-443.
1973 Morphological basis of alveolarcapillary gas exchange. Physiol. Rev., 53: 419495.
1974 A note on differentiation and divisibility of alveolar epithelial cells. Chest, 65:
19s-21s.
Woodside, G. L., and A. J. Dalton 1958 The
ultrastructure of lung tissue from newborn
and embryo mice. J. Ultrastruct. Res., 2. 28-54.
Документ
Категория
Без категории
Просмотров
0
Размер файла
896 Кб
Теги
growth, lung, postnatal, rat, autoradiographic
1/--страниц
Пожаловаться на содержимое документа