CHAPTER
III
REGULATION OF PARATHYROID GLAND FUNCTION
IN THE PIGEON Columba livia
INTRODUCTION
i
It
Is
known
that
the
secretion
of
the
parathyroid
gland
Is
t
regulated principally by serum calcium concentrations which brings an
elevation under low serum calcium concentrations and inhibition under
high serum calcium concentrations (Roth and Raisz, 1964, 1966; Roth et
al.,
1968;
Murakami,
1970;
Stoeckel
and
Porte,
1973;
Ream
and
Principato, 1981).
Parathyroid morphology has been studied in spontaneous as well as
experimental hypo and hyper calcemia groups in various species.
These
I
studies have disclosed changes in the parenchymal cells of the gland,
interpreted
atrophy
of
to be consistent with functional activity,
the
cells
which
are
mainly
indicated
by
inactivity and
variations
in
cytoplasmic density and cellular organelles, especially those concerned
with hormone synthesis (Capen and Rowland, 1968a, b; Roth et al., 1968;
Capen, 1971; Boquist, 1975).
In reptiles, birds and mammals there are good evidences for the
involvement of the parathyroid gland in calcium and phosphate metabolism
(Clark, 1970, 1983).
in
many
Studies on parathyroid function have been reported
amphibians
parathyroidectomy
and
and
reptiles
by
administering
subjecting
the
parathyroid
parathyroidectomized or intact animals (Peters,
1960,
Cortelyou,
1962;
Clark,
1965,
1968a,
the
animals
extract
to
to
1941; Cortelyou et al.,
1971a,
1972;
Sidky,
1966;
56
Oguro,
1970,
Nadkarni,
1975;
1987a,
Dubewar £t
Matsuda
et
al.,
1975;
al.,
Akbarsha,
1983;
Pathan and
1991). Parathyroidectomy
usually
I
results
in hypocalcemia
and hyperphosphatemia and ultimately leads to
tetanic convulsions with exceptions in turtles (Clark, 19,65).
a
few
studies
have
been
carried
out , to
test
the
In birds,
effect
of
1
parathyroidectomy in chickens, pigeons and ducks (Benoit: et al.,
Riddle
and
Newcomer,
Me
Donald,
1945;
Cherian
and
Cipera,
1968;
1941;
Hurst
1969; Anderson and Consuegra, 1970) and chick embryos
and
(Clark
and Mok, 1982; Mok and Clark, 1985) and most of these have shown'changes
in
serum
constituents
which
hyperphosphatemia and tetany.
excretion of
calcium and
result
Some
phosphate
in
studies have
on
hypocalcemia,
severe
been made on renal
parathyroidectomized
starlings
(Clark and Wideman, 1977) and quail (Clark and Sasayama, 1981).
In
addition
to
the
involvement
of
parathormone as
a
primary
calcium regulating hormone, there are number of factors which alter the
circulating level of calcium and thereby changing the functional status
I
of the parathyroid gland.
Vitamin D^ is an established hypercalcemic factor and it is known
that
1,' 25-
dihydroxycholecalciferol enhances
bone
demineralization
resulting in hypercalcemia and hyperphosphaturea (Schlumberger and Burk,
1953;
Robertson,
1975a,
b;
Dubewar
et al.,
1978;
Akbarsha and Gulam
Mohaideen, 1982) and Vitamin D^ stimulates intestinal calcium absorption
(De
Luca,
1976).
While
the
main
target
organs
for
1,
25-
57
dihydroxycholecalciferol are undoubtedly gut and bone, it appears that
physiological doses of the metabolite may also increase.renal tubular
reabsorption of phosphate and
independent
of
any
calcium,
an effect
which
is
parathyroid hormone action on this
(Omdahl and De Luca, 1973).
The Vitamin
probably
target organ
induced hypercalcemia has
been observed in amphibians, Rana pipiens
(Robertson, 1968a, b), Bufo
melanostictus (Akbarsha and Gulam Mohaideen, 1982), Rana jcyanophlyctis
(Pathan and Nadkarni, 1986), reptiles, Calotes versicolor, (Dubewar and
i
Suryawanshi, 1977), Uromastix hardwickii (Dubewar et al., 1978), Varanus
»
flaviscens (Swarup et al., 1987a; Pandey, 1988, 1991),
I
bird, Psittacula
l
psittacula (Swarup £t al.,
1987b) and mammals,
Suncus murinus, (Swarup
1
ii
and Srivastav, 1979) and rats (Wronski et al., 1986).
Estrogen
is
known
to
metabolism (Simkiss, 1967).
have
marked
,
I
effects
on
avian
calcium
Exogenously administered estrogens evoke a
i
phenomenal rise in total blood calcium in birds.t
(
The effect is greater
in females, but by no means confined to one sex' (Greep, 1963).
well known that in female birds,
It Is
the calcium content of the blood is
conspicuously increased during egg laying season ((Sreep, 1963; Simkiss,
1967;
Dacke,
show
pronounced
parathyroids
1979).
are
During peak reproductive activity, parathyroids
hypertrophy
in
a
state
(Urist,
of
1967).
active
In
the
secretion
laying
(Taylor,
hen
1965;
Nevalainen, 1969).
Exogenous estrogen treatment can promote parathyroid
functions
1967b;
(Clark,
Dubewar and Suryawanshi,
Dessauer,
1970;
1978; Akbarsha,
Ogurofc and
1983,
1985),
Uchiama,
1972;
stimulates the
i
i
58
secretory process in the parathyroid gland related to calcium metabolism
(Emura et al., 1982) and ovariectomy enhances morphological changes in
the parathyroid glands (Emura et al., 1984b).
Ethylene
dxamxne
tetra
,
acetic acid (EDTA) and sodium fluoride
i
(NaF) are the hypocalcemic factors which > decrease the !serum calcium
levels within one hour following administration (Montsko iet al., 1963a,
b; Baker, 1974; Isono et al.,
et
al.,
1985,
1987).
It
1976; Suketa and Kanamoto,j 1983; Monsour
is
reported
that
administration
decreases serum calcium rapidly in frogs, Rana esculent'a
of
EDTA
(Montsko et
i
al.,
1963a, b), R. rugosa (Isono et al., 1976) and the newt, Triturus
pyrrhogastor (Isono and Shoumura, 1973) with return to normalcy between
3 to 18 hours of treatment.
(Baker,
1974;
Administration of sodium fluoride to rats
Larsen et al.,
1981;
Monsour
et
al.,
1985),
rabbits
(Hirasawa and Niwa, 1985; Monsour «xt al., 1985, 1987) and human beings
(Simpson et^ al., 1980) leads to a rapid reduction in the serum calcium.
It
is further been shown that
parathyroids
of
EDTA and
NaF
treated animals had prominent mitochondria, secretory granules and other
cellular organelles and this is
activation of parathyroids
1
I
interpreted as an evidence for the
(Montsko e£ al., il963a, b; Isono et al. ,
1976; Ream and Principato, 1981).
The role of avian parathyroid glands at ultrastrxctural levels
''
i
are well documented in chicks, quail and love birds (Nevalainen, 1969;
i
59
Youshak and Capen, 1970; Gould and Hodges,
1972; Narbaitz,
1972; Fujii,
1970,
1971; Fuji! and Isono,
1975; Chan, 1977; Shoumura, 11974; Isono et
I
al.,
1978;
Wideman,
1980).
However,
elucidate
the
functional
relation
to
calcium regulation
experimentally
induced
experimental
significance
of
is
hypercalcemia
Alteration
to
parathyroid. structure
in
still
has
been
scanty.
Although,
studied
in
various
i
vertebrate classes (Robertson, 1968a, b; Dubewar and Suryjawanshi,
Dubewar et al.,
1978;
Swarup and Srivastav,
1979; Akbar'sha
1977;
and Gulam
Mohaideen, 1982; Wronski et al., 1986; Swarup at al., 1987a, b; Pathan
and
Nadkarni,
1986;
Pandey,
1988),
studies
are
restricted
to
i
ultimobranchial body and calcitonin cells.
Hence, the present study was
aimed to find out the induced hypo and hypercalcemia and their effect on
the parathyroid gland in order to elucidate the functional significance
of the same.
I
The studies were carried out at the level of light and
ultrastructural aspects of the parathyroid glands
Hypercalcemia was
induced
by
Vitamin
and
blood calcium.
in combination with calcium
chloride ( CaC^ ) and estrogen and hypocalcemia by EDTA and NaF.
In addition,
calcium,
at
the
,
parathyroidectomy was performed and |its effect on
level
of blood,
intestine
and
bone
to
explain
the
I
functional role of parathyroid gland in calcium regulation.
MATERIALS AND METHODS
Adult
pigeons,
irrespective
of
sex
were
obtained
i
!
from
local
60
dealer, acclimated to the laboratory condition for a week.
Food and
I
water were provided ad libitum throughout the period of investigation.
i
The experiments were carried out during the months of March to June.
The birds were
animals.
Group I:
divided into six groups, each group consisted of five
For group III only non-ovulating females were used.
The pigeons were given 0.1 ml of olive oil j(i.m.) for 10
l
days and served as controls for groups II & III.
Group II:
The pigeons received 6000 IU of Vitamin
Duphar-Interfran Ltd.,
Bombay,
(Arachitol,
India)/100 g body wt/day
(im) for 10 days in combination with 1% aqueous CaCl
(oral).
Group III:
Adult non-ovulating female pigeons were given 0.5 ml
t
Stilboesterol dipropianate (= 0.5 mg) (Vetostlerol, May and
Baker,
Bombay,
India)/100
g
body wt/day
for
10
days
(Intramuscular administration).
Group IV:
Animals received 0.2 ml of normal saline (im) for 10 days
and served as controls for groups V and VI.
Group V:
Animals received 0.2 ml of aqueous EDTA (im) (5 mg/100 g
body wt/day) for 10 days.
Group VI:
Animals received 0.2 ml of aqueous NaF (im)
(5 mg/100 g
i
61
body wt/day) for 10 days.
Prior
to
experimentation,
respective hyper and hypocalcemia.
pigeons were given mild
ether
the
doses
were
standardized
for
3 hours after the last dose,
anaesthesia
and
blood was
the
drawn in a
!
heparinized
tube
by
cardiac
puncture
for
calcium
estimation.
The
parathyroid glands were quickly excised for light and ultrastructural
studies as described previously.
Parathyroidectomy was performed according to the method of Smith
(1945), described in Zarrow et al. (1964).
with anaesthetic
ether,
The pigeon was anaesthetized
placed on the operation board and restrained
with rubber straps in such a position that its head was nearest to the
operator.
Feathers were plucked from the areas of neck,
the areas were sterilized with alcohol.
An incision was made through
the skin on the left side from the shoulder to sternum.
was separated from the furculum and pushed gently,
Trachea was
pulled
to
the midline with
crop sac and
the
to
The crop sac
the
mid [line.;
retractors and the area
!
posterior to the thyroid was freed so as to expose the carotid .artery
and the jugular vein.
The paired parathyroids were located together at
the region of the carotid bifurcation into external and internal carotid
artery and at the point where the carotid artery crosses the jugular
vein.
The glands were carefully electro-cauterized.
not to damage the blood vessels and vagus nerve.
Due care was.taken
There was a difficulty
i'
'
i
M I
,
I
if, :
62
to
separate
the
ultimobranchial
glands,
because
ofi
its
closer
I
association with the parathyroid glands and also to avoid.the chance of
the
presence
gland,
it
of
accessory
was
ultimobranchial
parathyroid
necessary
glands.
to
tissue
cauterise
Similarly,
in
both
the
the
ultimobranchial
parathyroid
the' right'1 gland
was
and
removed
by
retracting the gullet and trapping the head down on the right side of
the board.
After cauterization, the trachea,
crop sac and the gullet
were placed on their original position and the incisions were closed
1
with silk sutures. Streptomycin powder was sprayed over the area, where
1
the
incisions
were
bilateralectomy
maintained
under
made.
within
By
15
practice,
to
anaesthesia,
it
was
20
minutes,
using
paper
easy
when
cones
to
perform
the .animals
with 1 ether1
the
were
soaked
I
cotton.
Control animals were given similar operative trauma, excepting
-1
that their glands were not cauterized.
transferred to a well ventilated
cage.
After surgery, the animals were
The
animals
i
recovery within 1 to 3 hours after operation.
sh'owed
complete
i
i
The animals were’ not fed
' ' prior to and the entire duration of' the post operation,
i
for 2 days
but
they
were
provided
with
calcium
free
precipitation).
water
(obtained
by
oxalate
j
Blood was collected in a heparinized tube from both|sham operated
controls and parathyroid-ultimobranchialectomized (PTUBX) animals, after
6 hr, 12 hr, 24 hr, 48 hr, 72 hr and 120 hr of post surgery through the
pectoral" vein.
Plasma was separated by centrifugation and kept frozen
I
i
until further analysis.
The small intestine and the right femur were
/
<( DHACU7AQ.
z
I V-
*
63
removed and used for the calcium analysis from every 24 hours upto 120
hours of post surgery.
[
The small intestine of sham operated controls and PTUBX animals
was removed, freed from the luminal contents, washed in hold distilled
I
water
several
homogenized
times,
in
a
blotted
glass
free
homogenizer
of
water
with
centrifuged at 5000 rpm for 30 minutes.
and
cold
weighed.
distilled
It
was
water
and
The supernatant jwas collected
i
and used for calcium estimation.
The femur of sham operated controls and PTUBX birds were removed,
trimmed
weighed.
free
of
surrounding
flesh,
chopped
into
small
pieces
and
They were wet ashed with minimal quantity of nitric acid,
neutralized and diluted to 10 cc with distilled water.
Oj.2 ml of the
i
sample was added to
calcium (Clark, 1965).
1.8 ml
of distilled water
for
thd analysis of
The calcium content of the plasma, jintestine and
bone was determined spectrophotometrically according to the method of
Webster (1962).
Since it was difficult to obtain the urine from these pigeons
even by catheterization, the urinary calcium level could not be carried
out.
64
RESULTS
The
Plasma calcium:
I.
average
pigeon was 11.16 + 0.28 mg/100 ml.
plasma
calcium
of
the
control
Treatment for 10 days of Vitamin D3
in combination with CaC^ and estrogen elevated the plasma calcium into
16.26 + 2.44 mg/100 ml and 77.52 + 7.58 mg/100 ml respectively and EDTA
and NaF decreased to 6.04 + 0.15 mg/100 ml and 5.23 + 0.07 mg/100 ml
respectively.
The results were highly significant
(p < 0.001)
(Table
7).
!I.
Parathyroid morphology:
i)
Light microscopy:
The parathyroid glands of the control pigeons
(both olive oil and saline treated) exhibited the chief cells arranged
as cellular clumps or cords in compact manner.
by
a
thick
capsule
of
connective
tissue.
The gland was enclosed
The
chief
normal with distinct nucleus having one or two nucleoli.
cells
appeared
r
The cytoplasm
contained fine granules (Fig. 51).
The
parathyroid
glands
of Vitamin
+ CaC^ treated pigeons
showed degenerative chief cells with shrunken
was
faintly
stained
(Fig.
52).
pigeons
normal.
The
The cytoplasm
The cell and nuclear diameters ■ were
decreased significantly (Table 7).
appeared
nuclei.
parathyroid
Occasionally some of the chief cells
glands
of
the
estrogen
treated
showed the chief cells arranged as cellular cords with, wide
l
65
intercellular
spaces
and
sinusoids.
The
gland appeared foraminated.
The cytoplasm was faintly stained (Fig. 53).
Administration of EDTA and NaF induced a marked (change in the
parathyroid histology.
hyperactivity.
The
The chief cells of the gland showed the sign of
cell
and
nuclear
diameters
were j significantly
1
increased (Table 7).
The cells were arranged as, compact follicles.
The
cytoplasm contained fine granules (Figs. 54 & 55).
ii)
Ultrastructure:
The
parathyroid chief
pigeon contained glycogen particles,
cells
free ribosomes,
ot
the
control
a few secretory
granules, coated vesicles and lipid droplets dispersed in the cytoplasm,
Plasma membrane between the chief cells run a straight course and in
some places were folded.
was
situated
Mitochondria
at
were
the
Intercellular spaces were narrow ,
centre
scattered
with
patchy
throughout
the
The nucleus
chromati n
materials.
cytoplasm.
Granular
endoplasmic reticulum with parallel cisternae and Golgi apparatus were
distributed in
the
cytoplasm.
Vesicles
were
frequently
encountered
(Figs. 56-59).
The parathyroid glands of estrogen and vitamin
in combination
with CaCl^ treated birds, showed variations in the cytoplasmic cellular
configuration with the sign of relative under activity.
The cellular
i
organelles were Inconspicuous.
■,
Golgi apparatus and granular endoplasmic
|
i
reticulum were sparsely distributed, which were more frequently observed
66
in the cells
of Vitamin D3 + CaCl2
treated pigeons
(Figs.
61-62).
However, some of the chief cells of estrogen treated birds showed well
developed mitochondria and granular endoplasmic reticulum 1(Figs. 63-65).
I
Both the treatments showed a moderate distribution of free ribosomes,
occasional coated vesicles and secretory granules, vacuoles and lipid
droplets.
Intercellular
spaces were relatively wide and the
membrane pursued a straight line (Figs. 60-65).
The
parathyroid
glands of
EDTA
and
plasma
!
NaF
treated
birds
were
characterized by the presence of secretory granules and increased number
of cellular
organelles.
considerably
increased.
mitochondria
were welldeveloped
frequency of occurrence.
The tortuosity
The granular
and
of the
plasmaj membrane
was
endoplasmic reticulum and the
relatively
increased
in
their
The rough endoplasmic reticulum wa!s associated
1
with the nucleus and the mitochondria.
endoplasmic
reticulum were
The cisternae o': the granular
enlarged and arranged in parallel array.
1
1
1
|
Golgi apparatus was
distributed
coated vesicles and
small dense granules were observed in the. Golgi
area.
widely
in
the
i
cytoplasm.
I
Numerous
'
'
The secretory granules appeared closer to the plasma membrane and
freely
in
the perivascular spaces. Vesicles
(Figs.
67-75).
were
frequently observed
One of the striking observation in the
EDTA and NaF
treated pigeons was the occasional occurrence of intranuclear lamellae
in the nucleus ’(Figs. 66 & 72).
t—S>
67
III.
Parathyroidectomy;
A significant hypocalcemia was observed
following
12 hours
PTUBX which remained until 120 hours of observation period.
of
Of the 40
animals ectomlzed, 7 animals showed severe tetanic convulsions after 72
hours, followed by rolling of the body around with head knocked down the
ground.
pigeon
Eyes were kept open.
showed
tetany
after
The birds became kinked and rigid.
96 hours.
Out
of
8
birds] which
One
showed
tetany, 7 birds died within a day.
A significant decrease in the
intestinal calcium (p < 0.001) and a significant elevatiln in the bone
calcium (p < 0.001) were observed 24 hours after
PTUBX and remained
throughout the observation period (Table 8).
DISCUSSION
Calcium
is
the
principal
factor
in
controlling t the
A
decreased
secretory
I
activity
of
the
parathyroid
gland.
serum
calcium
i
concentration stimulates parathyroid hormone secretion and an elevated
concentration has an inhibitory effect.
Both effects are
apparent in
the serum parathormone concentration within minutes after experimental
alteration of the serum calcium concentration
(Sherwood at al.,
1966;
Targovnik et al., 1971; Blum et al., 1974; Habener et al.,! 1977).
The change in the serum calcium level in the present study, i.e.,
hypercalcemia
by
Vitamin
+
CaCl^
and
estrogen
treatment
and
68
hypocalcemia
by
EDTA and
NaF
are
similar
to
the
findings
in
other
vertebrate species (Greep, 1963; Montsko et al., 1963a, b;iClark, 1967b;
Simkiss,
1967; Robertson, 1968a, b; Dessauer, 1970; Oguro' and Uchiama,
1972; Baker, 1974; Isono et al.,
Swarup and Srivastav,
et al., 1985, 1987;
1976;
Dubewar and Suryawanshi,
1979; Akbarsha and Gulam1 Mohaldeen,|1982; Monsour
Swarup et al., 1987a, b; Pandey, 1988; 1991).
.
Vitamin
1977;
D~
induces
hypercalcemia
l
by
enhancing
bone
J
demineralization (Schlumberger
and
Akbarsha and Gulam Mohaideen,
1982),
(De
Luca,
1976)
and renal
tubular
Burk,
1953;
Robertson,
1975a,
b;
intestinal absorbtion of calcium,
resorbtion
(Omdahl and
De
Luca,
1973).
Exogenously
administered estrogen evokes an elevation in total
blood calcium levels in birds.
mg/100 ml
are
not
uncommon
facilitate the formation
of
Peak elevations to
(Greep,
a
1963;
Simkiss,
phospholipo—protein
approximately
1967).
100
Estrogens
(vitellin)
in i the
<
i,
liver of reproductlvely active females which binds calcium avidly and
its presence is
concentration
usually
(Simkiss,
associated with
1967;
Bentley,
an
increased
1976).
p asma
The
calcium
seven
fold
hypercalcemia due to estrogen action in the present studj ,
would have
resulted
complex in
from
the
large
amount
transit from the liver to ovary.
of
phosphoprotein-calcium
69
EDTA and NaF are the well known hypocalcemic substances.
EDTA is
a calcium chealating agent, brings the hypocalcemic by chealation (Isono
I
et al., 1976; Setoguti and Inoue,
1983).
The manner in |which the NaF
causes hypocalcemia is not clearly known.
However, histoljogical studies
I
suggest that the NaF
treatment
results
in necrosis
of 1 cells
in the
proximal tubules of the kidney (Takagi and Shiraki, 1982; Daston et al.,
1985).
With damage in this region one could speculate a reduction in
the kidney's ability to reabsorb calcium with a consequent hypocalcemia.
It is also suggested that fluoride induces hypocalcemia
ay stimulating
bone mineralization (Larsen and Thorsen, 1984; Larsen et al., 1978).
The
results
of
the
present
study
demonstrate
that
the
ultrastructure of the parathyroid chief cells changes due to variation
in the serum calcium concentration.
Parathyroids of dogs revealed that
the parathyroid chief cells respond to
the
alterations
of
the
serum
calcium concentrations within few minutes (Wild and Becker, 1980).
The
first visible changes occurred 15 minutes after incubation m media of
low
or
high
calcium concentration
in
parathyroid glands
of
gerbils
(Boquist, 1977) and ultrastructural changes became obvious as early as 2
to 5 hours after alteration of the serum calcium concentration (Oldham
et al., 1971).
The principal changes occurred m the parathyroid glands of the
pigeon
are
the
hypercalcemia,
suppression
as
revealed
of
the
by
the
parathyroid
sparsely
chief
cells
distributed
during
cellular
, i
70
organelles and wide intercellular spaces and an activation of the chief
cells under hypocalcemia as
revealed
by
the well
developed cellular
I
organelles and secretory granules in most of the chief cells.
The increase in the cytoplasmic volume, floccular Isubstances in
,
i
the intercellular spaces, granular endoplasmic reticulum, jmitochondria,
I’
well developed Golgi apparatus and small dense granules in the Golgi
area indicate a hyperfunction of the parathyroid chief cells
1969;
Furuta,
Jsono et^ al.,
and Raisz,
1971;
1971,
1966;
Youshak and
Capen,
1970;
Fuji! and Isono,,
1976; Iwatsutsumi, 1971; Capen et al
,
i
|
Mazzocchi ert al.,
(Tanaka,
1967; Nevalainen,
1972;
1965;
i
Roth
1969; Fetter and
Capen, 1970).
The Increased tortuosity of the plasma membrane, 'occurrence of
coated
vesicles
and
secretory
granules,
especially
thle vesicles
and
granules near the plasma membrane are the characteristic feature of the
active chief cells (Capen et al.,
1965; Nakagami, 1965; Roth and Raisz,
1966; Youshak and Capen, 1970; Isono et al., 1977).
the
changes
in
tortuosity
of
the
plasma membrane
It is reported that
is related to the
uptake of aminoacid and the release of parathormone through1 the plasma
membrane
(Murakami,
1970).
An intense alkaline phosphatasse and ATPase
activity in the area of tortuosity of the plasma membrane suggests the
'
r
1
1
metabolic transport of material across the plasma membrane (Setoguti et*
al., 1980).
I
71
In most glandular cells,
ribosomes
and
reticulum.
stored
in
the
secretory protein is
cisternae
of
the
synthesized
at
granular endoplasmic
The newly synthesized secretory protein is transferred from
the granular endoplasmic reticulum to the Golgi apparatus, which derives
the secretory granules (Muager and Roth, 1963; Capen et al., 1965; Roth
,!
and Raisz, 1966; Stoeckel and Porte,
1969;
Youshak
Shoumura,
and
Capen,
1970;
'
,
.
1967a, b; Nakagami,, 1967; Tanaka,
Nakagami 1 et
al.,
1971;
Isono
and
1973).
The number of secretory granules in the parathyroid
!
gland increases upon experimental stimulation (Montsko et jal., 1963a, b;
Roth and Raisz,
1964;
Capen et al.,
1965;
Isono eit al, ,
1969,
1971,
1976, 1990).
Coated vesicles
are
the
specialized
sites
for
the
uptake
of
protein.
The coated regions of the plasma membrane [are the sites
specialized for receptor mediated binding and uptaki of specific
macromolecules
(Anderson
et
al.,
1977).
Uptake
of
receptor
bound
proteins in coated vesicles is the ultimate deposition of the protein in
specific organelles or transported across the cell and released into the
I
blood stream (Goldstein et al., 1979).
In the present study, the experimental ihypercalcemia
shows the
chief cells of the parathyroids with signs of low, functional activity as
l"1'
evidenced by the incospicuous appearance
reticulum,
Golgi
apparatus
functional
activity
is
and
obviously
of the
111
secretory
due
to
granular endoplasmic
‘
granules.
the
The
suppression
(
1
decreased
of
the
72
parathyroid glands by hypercalcemia.
The hypocalcemia shows the chief
cells with signs of hyperactivity as evidenced by the increase in the
1
number of cell organelles, secretory granules and coatedjvesicles.
It
could be suggested that the secretory function of the parathyroid gland
jl
is accelerated from depressed serum calcium levels and temporary release
of many secretory granules
is
triggered
in
order
to
keep
the
serum
i
calcium at normal level as suggested by Isono et al. (1976!).
Since
the
granular
secretory granules and
endoplasmic
coated vesicles
reticulum,
are
directly
Golgi
involved
i
secretion of
protein
(Palade,
apparatus,
in
the
!i
1975) and consequently ofi parathormone
I
(Habener
nt
al.,
1977),
the
findings
in
the
present
investigation
suggest that the rapidly occuring ultrastructural changes are probably a
reaction of parathyroid chief cells to alteration in the ambient calcium
concentration
to
promote
or
suppress
the
parathormone
secretion.
However, the presence of some of the chief cells in the experimental
hypercalcemic birds with structural signs of moderate or high functional
activity indicate that there is no overall inactivity of the parathyroid
glands
even after
believed
atrophy
that
in
the
administration
existence
of
it
of
the
experimental
is
suppression by hypercalcemia.
impossible
parathyroid
induce
glands
hypercalcemic
functional
to
of
in
complete
intact
substances
cycles
a
the
animals
probably
It
is
inactivity
or
by
repeated
because
parathyroid
chief
of
the
cells.
Similar findings have been reported in the parathyroids of cattle under
Vitamin
induced hypercalcemia (Capen, 1971) and rats in organ culture
73
(Roth and Raisz, 1966; Roth, 1971).
The occasional occurrence of the
intranuclear
lamellae
in
the
active chief cells of the parathyroid glands induced by EDTA and NaF
does
not
allow
any
suggestion
about
their
possible
functional
significance in the parathyroid glands.
Hypocalcemia, hyperphosphatemia, tetany and death are the primary
responses to
parathyroidectomy,
calcium
regulating
(Sidky,
1966;
endocrine
since
parathyroids
gland
in
reptiles,
1969;'
,
Clark^ !(si970,
1
Clark
et
al.,
i
{
Dantzler,
1972;
Oguro,
1970,
1972,
1975;
1
are
the
birds
principal
and
mammals
1
1971a;
Clark
and
, , l, !>
)
Clark
and
Dubewar et al., 1978; Singh and Kar, 1979; Akbarsha,
Wideman,
1983;
1977;
Pathan and
Nadkarni, 1987a).
Parathyroidectomy leads to impaired ability to mobilize calcium
from
the
reduced
bones,
kidneys
concentration
of
and
intestine
calcium
and
ions
in
hence
the
hypocalcemia.
extracellular
produces hyperexcitability of the neuromuscular system
tetany, an involuntary twitching of the muscles.
The
fluid
which leads to
Unless
the measures
I
are
taken to
elevate
the
calcium levels
in
the
blood,
death
'
often
results from asphyxiation due to spasm of the laryngeal muscles (Turner
and Bagnara, 1976).
1
In the present study, the characteristic hypocalcemia, tetany and
74
death observed in the pigeon, jC. livia as in other vertebrate species
suggest
the
dominant
role
of
the
parathyroid
gland
in
calcium
t
regulation.
Hypocalcemia would have resulted from the impaired ability
to mobilize calcium from the bones,
kidneys and intestine,
the major
target organs of the parathyroid glands as evidenced by the accumulation
of calcium in the bone and reduced calcium in the intestine.
It
is
obvious to observe tetany, since there is no calcium supplement during
the course of
water.
The
investigation
diminished
by
starvation and
transport
of
calcium
calcium
from
free
the
drinking
intestine
as
evidenced by the decrease in calcium from the intestine in the present
study,
is due in part to the inability of the kidney to form,
dihydroxycholecalciferol,
absorption,
a major
factor
for
the
intestinal
1, 25calcium
since the parathyroid gland is essential for the synthesis
of 1, 25- dihyroxycholecalciferol from the kidneys.
SUMMARY
Induced hypercalcemia by Vitamin
in combination with calcium
chloride and estrogen and hypocalcemia by EDTA and NaF and their effects
on parathyroid gland have been studied by light as
microscopy and
the
effect
on
the
blood
elucidate the functional significance of
well
as
electron
calcium levels,
in order to
the
gland.
parathyroid
The
effect of parathyroidectomy on calcium at the level of blood, intestine
and bone has also been investigated to explain the functional role of
parathyroid gland in calcium regulation.
75
Induced hypercalcemia showed an under activity of the parathyroid
chief cells as revealed by the inconspicuous cellular organelles.
Golgi
apparatus and granular endoplasmic reticulum were poorly defined.
ribosomes,
coated
distributed.
vesicles
Intercellular
and
secretory
spaces
granules
were1
Free
poorly
were wide and the plasma membrane
i
pursued a straight line.
Induced hypocalcemia showed the parathyroid gland of hightened
activity,
as revealed by the presence of increased tortuosity of the
plasma membrane,
granules.
increased
Mitochondria,
number
closer
to
the
coated
vesicles
and
secretory
granular endoplasmic reticulum and the Golgi
apparatus were well defined.
appeared
of
Coated vesicles
plasma
membrane.
and
secretory granules
Internuclear lamellae were
occasionally observed.
Parathyroid-ultimobranchialectomy
(PTUBX)
showed
a
significant
hypocalcemia following 12 hours of ectomy which remained until 120 hours
of
observation period.
Tetanic
convulsions,
followed
observed after 72 hours of operation in some animals.
decrease
in intestinal
calcium and
a
significant
by
death
was
A significant
elevation
in
bone
calcium were observed 24 hours after PTUBX which remained throughout the
observation period.
7:
D 0+CaCl„, Estrogen, EDTA and NaF on plasma calcium level and cell and nuclear
11.85 + 0.23
Control (saline)
8.47 + 0.09*
8.68 + 0.07*
6.04 + 0.15*
5.23 + 0.07*
EDTA
NaF
* p < 0.001.
3.21 + 0.06*
5.48 + 0.08*
5.37 + 0.06*
5.33 + 0.16*
77.52 + 7.58*
Estrogen
3.78 + 0.07*
4.47 + 0.03
5.25 + 0.05*
16.26 + 0.44*
Vit. Dg + CaCl2
4.56 + 0.10
6.57 + 0.07
6.62 + 0.13
(pm)
(pm)
11.16 + 0.28
Nuclear diameter
Cell diameter
Control (olive oil)
Plasma calcium
(mg/100 ml)
(Values are SEM of five animals)
diameters of the chief cells of parathyroid gland of the pigeon, C. livia .
Effect of Vitamin
Treatment
Table
Ta
i«1>
JZ
m
caU
c
CM
H
VO
«
o
-M
o
+1
hs.
sr
f-v
r->
H
o
4-1
VO
o
Mf
*CM
o
o
+1
o
CM
*
•H
CM
o
sf
«CM
o
o
4-1
*
rM
o
«
«CM
O
o
o
4-1
«
tn
H
o
+1
CO
VO
vn
o
o
m
in
•—t
I
i
i
t
CO
•3H
H
o
o
o
4-1
l-H
**3
O
o
o
CM
CM
o
+1
m
co
>—<
**p < 0 01
»n
«<T
* p < 0 001
sr
15.70 + 0 34*
«Os
o
o
+1
+ 0 01*
o
+1
o%
*3u*>
0 14
6 75 + 0.07*
H
«
o
o
+1
o
CM
(mg/g)
0 05*
CM
+
oo
*$•
37
«CM
Intestine
7
r-.
+ 0 22*
CM
Bone
(mg/g)
9 86
Hours after parathyroidectomy
bone and intestine
vO
O'
Plasma
(mg/100 ml)
Calcium
Effect of parathyroidectomy on the calcium level of plasma,
(Values are SEM of 5 animals).
o
CM
*CM
O
O
+1
m
H
>n
O
4-1
rH
as
O
4-1
co
m
CM
O
4-1
VO
CM
m
i— 4