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Response of hamster thyroid light cells to plasma calcium.

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Response of Hamster Thyroid Light Cells to
Plasma Calcium '
Department of Anatomy, College of Medicilte,
University of Illinois at the Medical Center,
Chicago, Illinois
Light cells in the hamster thyroid gland were examined by electron microscopy and histochemical methods in control, hypercalcemic and
hypocalcemic animals. Elevation of plasma calcium levels stimulated a marked
depletion of light cell granules as detected by electron microscopy and silver impregnation. In the hypercalcemic state the size and number of light cells did not
differ from that of control animals. Hypocalcemic hamsters showed a significant
increase in light cell numbers with marked hypertrophy and hyperplasia of this
cell type. These observations support the view that the light cell in the hamster
thyroid is associated with thyrocalcitonin secretion.
The discovery of thyrocalcitonin, the hy- have demonstrated a specific binding of
pocalcemic, hypophosphatemic hormone anti-calcitonin within light cells of porcine,
present in mammalian thyroid glands ovine and canine thyroid glands (Bussolati
(Hirsh et al., '63; Foster, MacIntyre and and Pearse, '67; Kracht et al., '68) as well
Pearse, '64) has initiated a search for the as in man (Kalina et al., '70).
The presence of the light cell as a specell type responsible for this product. At
the present, certain data indicate that cific cell type differing in structure from
thyrocalcitonin (TC) is secreted by a cell the follicular cell was first described by
type referred to by a variety of names, the Wissig ('62) and Young and Leblond ('63).
most common terms being, the parafol- Stux et al. ('61) had previously shown that
licular, light or C cell. Changes in certain within an hour after injection of thyroidenzyme systems have been demonstrated stimulating hormone, rat follicular cells
in these cells in thyroid glands of dogs per- acquired large amounts of intracellular
fused with blood having an elevated cal- colloid, whereas, the light cells did not.
cium concentration (Foster, Baghdiantz, Young and Leblond ('63) demonstrated
Kumer, Slack, Saliman and MacIntyre, that in the rat these cells incorporate much
'64). Electron microscope studies indicate less H3-leucine than do follicular cells. In
that the granule content of these cells in several species of animals (Falck et al.,
the rat varies inversely with the concen- '64; Ritzen, '65; Larson et al., '66; Pearse,
tration of plasma calcium; elevated cal- '68; Owman and Sundler, '68) an addicium levels initiating a marked degranu- tional distinguishing characteristic is the
lation (Matsuzawa, '66; Ericson, '68) and marked uptake by the light cell of serotonin
reduced calcium levels producing an ac- precursors and their subsequent conversion
cumulation of granules (Wetzel and to serotonin.
Gittes, '66; Cameron, '68). Pearse ('66),
In an earlier study (Biddulph et al., '70)
Capen and Young ('67), Nunez and Gould we reported the presence and relative con('67) and Young and Capen ('70) have centrations of TC in the thyroid gland of
demonstrated that under certain conditions the hamster, In addition, we found that
changes in granular content may occur in
Received July 15, '71. Accepted Nov. 22, '71.
light cells of some other species also. In1 Supported in part by College of Medicine =ant
creased number of these cells was observed 2-46-3310-3.02
and Graduate College grant 2-41-33-103-13of the Universitv of Illinois a t the Medical Center.
in osteopetrotic mice following treatment Chicago,
with parathyroid extract (Marks and
2 Present address: Department of Anatomv. Bowman
Gray School of Medicine of Wake Forest University,
Walker, '69). Immunofluorescent methods Winston-Salem, North Carolina 27103.
ANAT. REC.,173: 2544.
the thyroid gland in this species, as in the gram of body weight in order to investigate
rat (Hirsch and Munson, '69), could restrict mitotic activity. The tissue was removed
the hypercalcemic response to exoge- one hour later and prepared for autoradiognous parathyroid hormone (PTH) pre- raphy, using the film stripping method of
sumably because of the release of TC. Be- Pelc ('56). Sections, prior to stripping had
cause of these findings and since little been stained for the Feulgen reaction, or
information is available concerning either were stained with 0.1 % toludine blue,
normal morphology of the hamster light through the emulsion after development.
cell or its sensitivity to changes in blood Tissues fixed for electron microscopy were
calcium concentrations, we have conducted dehydrated through ascending concentraa morphological study of this cell type. The tions of ethyl alcohol, transferred to propypurpose, therefore, was twofold: (1) to lene oxide and embedded in Epon. One
determine the normal distribution and micron sections were cut, stained with
morphological properties of these cells in toluidine blue and examined in order to
the hamster and ( 2 ) to examine the mor- localize areas containing light cells. When
phological effects produced during altera- these areas were localized, sections were
tion of plasma calcium levels in vim.
cut at approximately 300 A with a PorterBIum
microtome, mounted on 200 mesh
copper grids and stained with uranyl aceA total of 83 male hamsters weighing tate for examination under an RCA EMU-2
100 to 125 gm were used in this study. electron microscope.
Animals were divided into three groups
consisting of ( 1 ) untreated controls, ( 2 )
parathyroid extract (PTE)-treated and ( 3 )
Control light cells
bilaterally nephrectomized animals. PTE
Light cells were readily identified with
treatment was utilized to induce hypercalcemia which was followed in 23 animals the light microscope in hamster thyroid
during a 51 hour period. PTE was injected glands because of their relatively weak
subcutaneously in three doses of 170 units cytoplasmic staining with either toludine
each at 0, 12, and 24 hours. Forty-two blue or PAS (figs. 1, 2). Intracellular colanimals were bilaterally nephrectomized in loid droplets which were intensely stained
order to induce hypocalcemia which was in follicular cells were lacking in all light
followed over a 51 hour period following cells observed. In most of these cells cytonephrectomy. All blood samples were plasmic RNA, which stains metachromatianalyzed for total plasma calcium by flame cally with toluidine blue and is labile in
ribonuclease was scarcely demonstrable but
Thyroid glands were removed from con- occasionally cells were observed in which
trol animals and from both experimental a polarized network of RNA was promigroups 51 hours following treatment. Tis- nent, usually near the large lightly stainsues from each group were fixed by im- ing nucleus (fig. 3). These cells, consistmersion in 5% glutaraldehyde and post- ently larger than follicular cells, were oval
fixed in osmium tetroxide ( 0,04)for study or pyramidal in shape, and in PAS-toluiby electron microscopy. Other tissues from dine blue preparations, were invariably
each group were impregnated with silver located within the basement membrane of
according to the method of Nonidez ('39) thyroid follicles (figs. 1, 2). Some light
or were fixed in Carnoy's solution and cells occupied an epifollicular position
either stained for ribonucleic acid (RNA) while others were wedged in between folwith 0.1% toludine blue with or without licular cells. Occasionally small groups of
ribonuclease or were stained with a com- light cells appeared to be located in an
bination of toluidine blue and periodic acid interfollicular position. Without exception,
Schiff (PAS) following amylase treatment. however, serial sectioning demonstrated
Five additional animals, 51 hours following these cells to be small outpocketings of
nephrectomy, and four untreated, control light cells maintaining a definite anatomihamsters were injected with 1.24 ,&i of ~3 Eli Lilly Company 100 U.S.P. Units per cm3.
H'-thymidine (S. A. 10,000 mc/mM) per
4 Amersham Searle korporation, Des Plaines, Illinois.
cal position within thyroid follicles. Therefore, no true parafollicular or interfollicular
light cells were observed in the hamster
thyroid gland. In contrast to follicular
cells, the nuclei of these cells were appreciably larger, lighter stained, and contained
two to three discrete Feulgen-positive,
heterochromatin bodies adjacent to the
nuclear membrane (figs. 2, 3 ) .
Following application of Nonidez method
the large expanse of chromophobic light
cell cytoplasm contained numerous, small
argyrophilic granules (fig. 4). These granules were consistently present in numbers
large enough to clearly differentiate the
cytoplasmic boundaries of the light cells,
since cytoplasmic material in follicular
cells was not stained by this procedure
(fig. 4).
Electron microscopy confirmed the presence of numerous membrane-limited granules and the absence of colloid droplets in
the light cell (fig. 5). Electron dense
granules were numerous and measured
approximately 200 my in diameter. In
control animals a random distribution of
granules rather than a polarized arrangement existed in the light cell cytoplasm.
Small numbers of empty vesicles were observed as well as what appeared to be
intermediate stages between empty and
electron dense granules (fig. 6). However,
a polarized network of granular endoplasmic reticulum was usually present near
the nucleus corresponding to its position
observed with the light microscope. Small
numbers of free ribosomes, occasionally in
the form of polysomes, were sparcely scattered in the cytoplasmic matrix. Golgi
membranes were well developed and usually associated with small vesicles containing a material of varying density (fig. 6).
The distribution of light cells in hamster
thyroids was studied in serially sectioned
material. Light cells were observed to be
consistently located within a relatively
small region of each thyroid lobe usually
adjacent to the laterally located parathyroid
gland. The superior third as well as the
extreme inferior portions of the thyroid
were normally lacking in this cell type.
The concentration of light cells in the light
cell rich area was calculated from several
randomly selected fields in each gland in
which, with the aid of a reticulated grid,
all follicle and light cells were counted.
The average light cell concentration as
calculated by this method was 17.3 light
cells/100 cells examined or 17.3% (table
2). A large cystic structure reminiscent of
the ultimobranchial body was usually
found in the central part of the light cell
rich area with follicles containing light
cells scattered around it in a radiating pattern. The cystic exudate of this structure
was PAS-positive and usually contained
cellular debris and extruded nuclei. A
silver positive granular material, absent in
thyroid colloid, was, also, present in
abundant quantities. The epithelium upon
the papillae extending into the cystic
structure varied in thickness from pseudostratified to squamous cells. Rarely could
light cells be detected within its epithelial
Effects of hypercalcenzia
Animals injected with PTE responded
with a moderate elevation in plasma calcium 24 hours following the initial injection (table 1). During the remaining
interval (24 to 51 hours), calcium levels
decreased from the 24 hour value but
remained elevated relative to control
Light cells in this group of hamsters did
not differ significantly in number, size, or
distribution from those in control animals.
However, changes in two cytoplasmic constituents were observed. Light microscopy
revealed a diffuse metachromatic response
in the cytoplasm of these cells when stained
with toluidine blue which was removable
by treatment in ribonuclease. Cells lacked
a polarization of RNA with the entire cytoplasm demonstrating a relatively strong
RNA response. Electron microscopy revealed an abundant and diffuse distribution of ribosomes and endoplasmic reticulum in the majority of these cells (fig. 14)
in contrast to controls (fig. 6) thus confirming observations of these differences
with the light microscope. In addition to
the dispersion of cytoplasmic RNA in these
cells, an obvious reduction in granule
content was present in most light cells
examined. Silver impregnation of these
glands demonstrated an extremely sparce
number of granulated cells (fig. 8) relative
to control glands (fig. 7). Only rarely
Plasma calcium determinations in hamsters
plasma calcium
NO of
concentration and
determrnations standard error
mg per cent
9.70 f0.22
12 hours
24 hours
36 hours
42 hours
48 hours
9.16 f0.31
6.88 & 0.24
7.20 C 0.26
6.16 -C 0.26
5.72 & 0.31
10.71 2 0.30
10.92 k 0.30
51 hours
PTE treated
12 hours
24 hours
36 hours
51 hours
could a light cell be found in which sufficient granules were present to outline its
cytoplasmic boundaries. Electron microscopy confirmed the depletion of granules
in these cells. Most cells observed contained only a few small granules usually
lacking normal density in areas of the
Golgi apparatus (fig. 14). Mature granules
typical of those in control cells (fig. 6)
were markedly reduced. Follicular cells in
this group appeared unchanged from controls in their structural characteristics.
evident. Large masses of light cells were
present which tended to widely separate
normally closely adjacent thyroid follicles
(figs. 9-11). A definite correlation was
noted between increased amounts of silver
granulated cytoplasm and increased light
cell numbers. The concentration of light
cells in the light cell rich area increased
from 17.3% in control glands to 34.8%
(table 2). The mitotic index and n u m k r
of light cell nuclei incorporating H3-thymidine increased approximately seven and
ten fold respectively (table 2 ) indicating
that increased numbers of these cells had
been derived through replication of preexisting light cells. Hypertrophic changes
were also evident in many of these cells
with marked increases occurring in cytoplasmic volume (figs. 12, 13). Ultrastructural characteristics of these cells (figs. 15,
16) resembled that of control light cells
(figs. 5, 6). Polarized networks of granular endoplasmic reticulum and large numbers of membrane-limited granules were
the predominant characteristics observed.
No attempt was made in this study to
quantitate granule density (number of
granules per unit cytoplasm), however,
observations based on both silver and electron microscopic preparations indicated
that granule density in these cells (figs. 9,
15, 16) was at least as great as in control
light cells (figs. 6, 7 ) .
Follicular cells in this group remained
normal in mitotic activity, and in general
Effects of hypocalcemia
The progressive drop in plasma calcium
levels during a 51 hour period following
bilateral nephrectomy is demonstrated for
this group of animals in table 1. By 51
The presence of light cells comparable
hours, post surgery, a 4 mg per cent de- in structural properties to those described
crease in plasma calcium had occurred and in several other mammalian species was
determined in hamster thyroid glands. Lack
tissues were removed for observation.
Changes in both the number and size of intracellular colloid, polarization of cyof light cells in animals of this group were toplasmic RNA, presence of a specific type
E f f e c tof nephrectomy and parathyroid extract on light cells of the hamster thyroid gland
nephrec tomized
Per cent
light cells
No. thyroid glands
e.tam:n-d per -roup
34.8 f8.2
Mitotic ind-x2
Thymidine index 3
0.11 f0.03
0.31 f0.04
0.68 f0.07
2.79k 0.32
1 Average light cell conzentration i n light cell rich area of thyroid
2 Number of mitotic figures per 100 light cells examined.
3 Number of H3-thymidine labeled nuclei per 100 light cells.
Standard error.
of granule, difference in nuclear structure
and distribution within the follicle all distinguish this cell type from the more numerous follicular cells. Similar cytological
characteristics have been observed for this
cell type in the rat (Wissig, '62; Young and
Leblond, '63; Matsuzawa, '66) mouse (Sato
et al., '66; Walker, '66), dog (Foster,
Baghdiantz, Kumer, Sack, Soliman and
MacIntyre, '64; Pearse, '66), pig (Bussolati and Pearse, '67; Young et al., '68),
cow (Capen and Young, '67; Young and
Capen, '70), bat (Nunez and Gould, '67)
and man (Kalina et al., '70).
In the hamster, light cells cluster around
an apparent remnant of the ultimobranchial body and remain relatively localized
in their distribution within the thyroid.
This fact may be of significance since recent experiments (Carvalheira and Pearse,
'68) indicate that the embryonic ultimobranchial in mammals is the source of
these cells. A similar localization has been
reported in mice (Falck et al., '64; Larson
et al., '66; Marks and Walker, '69) whereas, in most other mammals, a random
distribution of light cells occurs throughout
the thyroid gland.
The effect of elevated calcium levels on
the cytochemistry and ultrastructure of
hamster light cells indicates a significant
discharge of granular secretion in response
to hypercalcemia. Loss of both silver and
electron microscopic granules in these cells
suggest that release is stimulated to a
greater extent than resynthesis leading to
depletion of the secretory product. This
phenomenon has been reported to occur
in these cells in the rat (Matsuzawa, '66;
Ericson, '68), dog (Pearse, '66), and cow
(Capen and Young, '67; Young and Capen,
'70) under similar conditions. The dispersion and increase in cytoplasmic RNA
observed in hamster light cells subjected
to hypercalcemia may represent a stage of
recovery of these cells following hypercalcemia necessary for renewing their content
of secretion. Increased amounts of cytoplasmic RNA have been described in hyperactive light cells from cows with parturient
paresis (Capen and Young, '67), and in
canine light cells cultured in a high calcium media (Bussolati et al., '70). Other
cells were observed in the present study
which lacked both granules and an ex-
tensive RNA content. Large numbers of
empty vesicles were present which may
represent an earlier stage following degranulation. Similar vacuolization has
been reported for dog thyroid cells following induced hypercalcemia (Pearse, '66).
The net reduction in stored secretory
granules in the hamster light cell during
hypercalcemia is in accord with the proposed storage of TC within the light cell
granule (Matsuzawa, '66) since Gittes et
al. ('68) have reported as much as 70%
decrease in TC concentration of rat thyroid
glands within two hours after inducing
hypercalcemia by oral calcium administration. While a direct effect of the exogenous
PTH on degranulation cannot be ruled out
in the present study, convincing evidence
exists from both in vivo (Care, '65; Care
et al., '67; Cooper et al., '71) and in vitro
(Feinblatt and Raisz, '71) studies that
hypercalcemia is the primary factor stimulating release of stored TC from the thyroid
gland. We have previously shown (Biddulph et al., '70) that the release of TC
from the thyroid gland of the hamster
could effectively restrict hypercalcemia resulting from the administration of exogenous PTH.
Hypocalcemia had a profound effect on
the hamster light cell. Increased cell numbers (which could be correlated with comparable increases in mitotic activity) and
hypertrophy were the principle effects
noted and resulted in a net increase in
amounts of granulated light cell cytoplasm
within the thyroid gland of this species.
These morphological observations correlate
well with the findings of Gittes et al. ('68)
which demonstrate that the TC content of
rat thyroids exposed to prolonged hypocalcemia is markedly increased. Antithyroid
drugs, known to inhibit TC release (Care
et al., '66) have also been found to increase
granule content of pig thyroid light cells
(Young et al., '68). From these data, it
appears that lowered calcium levels may
suppress the release of TC to a greater
extent than suppression of synthesis thus
leading to a progressive accumulation of
secretion products within the thyroid gland.
This hypothesis is dependent on at least
some secretion occurring in normal cells
at normal plasma calcium concentrations.
Cooper et al. ('71) have recently shown by
radioimmunoassay small circulating levels
of TC in normocalcemic pigs.
Biddulph, D. M., P. F. Hirsch and P. L. Munson
1970 Thyrocalcitonin and parathyroid hormone in the hamster. In: Calcitonin: Proceed.
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Some observations on the light cells of the thy.
Photomicrograph of light cell rich area in control hamster thyroid
gland. Several light cells (arrows) may be distinquished because of
their chromophobic cytoplasm and larger cell size in relation to follicle
cells, Also, note that these cells lie within the basement membranes of
follicles with which they are associated. Toluidine blue-PAS. x 470.
Photomicrograph at a higher power of part of the field in figure 1.
Note that light cell nuclei (arrows) are larger than nuclei of follicular
cells (F). One pole of the light cell rests on the basement membrane
( B M ) while the opposite abuts on a border of the follicular cell cytoplasm. Toluidine blue-PAS. x 1,100.
3 Light cell from a control hamster may be seen i n lower center of the
field (L). Note the lack of cytoplasmic metachromasia with the exception of a polarized network (arrow) visible just above the nucleus.
Staining of this network was prevented by prior treatment with ribonuclease. Toluidine blue. x 1,100.
Photomicrograph of a follicle containing light cells in a control hamster. Tissue, impregnated with silver, demonstrates argyrophilic granules present in the light cells (arrow). Granules are numerous and
specific for the light cell cytoplasm. Nonidez silver impregnation.
x 1,100.
D. M. Biddulph and H. C. Maibenco
Electron micrograph of a light cell ( L ) from a control hamster. These
cells lack colloid droplets ( C ) and the dilated endoglasmic reticulum
(ER) of follicle cells (F). The cytoplasm of the light cell is less electron dense and it contains numerous small electron dense granules.
Glutaraldehyde and osmium fixation. x 3,825.
Electron micrograph of a light cell from a control hamster thyroid
gland. Note numerous membrane-limited granules and paucity of
granular endoplasmic reticulum (ER). Prosecretory type granules
(arrows) may also be observed. Glutaraldehvde and osmium fixation.
x 15,000.
D. M. Biddulph and H. C. Maibenco
7 Light cells (arrows) from a control hamster thyroid gland following
silver impregnation. The cytoplasm of these cells contains many small
argyrophilic granules not present in follicle cells, Granules are heavily
concentrated throughout cytoplasm. Nonidez silver impregnation
x 1,100.
Light cells (arrows) from hamsters exposed to elevated plasma calcium levels. Note that granules are markedly decreased in these cells
in relation to control cells (fig. 7). Nonidez silver impregnation.
x 1,100.
Light cells (arrows) from hamsters rendered hypocalcemic by nephrectomy. Large masses of these densely granulated cells may be observed in amounts exceeding control thyroid glands. Nonidez silver
impregnation. x 1,100.
D. M. Biddulph and H. C. Maibenco
Photomicrographs of thyroid glands of bilaterally nephrectomized
hamsters. Large masses of light cells may be observed. In relation
to control glands (fig. 1) a twofold increase in the number of
these cells occurred. Mitotic activity (arrows) in present and was
seven rimes as frequent as i n controls. Toluidine blue-PAS. x 600,
12 Light cell of bilaterally nephrectomized hamster in mitosis (arrow). Note the hypertrophy and large numbers of argyrophilic granules within the cytoplasm. Nonidez silver impregnation. x 1,300.
13 Light cell from a bilaterally nephrectomized hamster (arrow).
Note the long cytoplasmic processes densely filled with granules
adjacent to the basement membrane (BM). Nonidez silver impregnation. x 1,100.
D. M. Biddulph and H. C. Maibenco
14 Electron micrograph of a light cell from a hypercalcemic hamster.
This particular cell contains a very few granules (arrow), f o r m h g
i n the area of the Golgi apparatus (G). Granular endoglasmic reticulum (ER) is diffuse and increased relative to control cells. (fig. 6).
Glutaraldehyde and osmium fixation. X 20,000.
D. M. Biddulph and H. C. Maibenco
Electron micrograph of portions of three light cells from a nephrectomized hamster. Granules are present i n large numbers filling, the cytoplasm of a cell in the center of the field. Polarized networks of rough
endoplasmic reticulum (arrows) are present in cells at the upper right
and upper left. Glutaraldehyde and osmium fixation. x 5,000.
16 Electron micrograph through a cytoplasmic process of a light cell
from a nephrectomized hamster. In addition to large numbers of
dense granules, some less electron-dense granules (arrows) may be
observed. Ribosomes and endoplasmic reticulum are sparce. Glutaraldehyde and osmium fixation. x 30,000.
D. M. Biddulph and H. C. Maibenco
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hamster, response, light, calcium, thyroid, plasma, cells
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