Oxidative stress in hypopituitary dwarf mice and in transgenic mice overexpressing human and bovine GH


Carlson, J.C.; Bharadwaj, R.; Bartke, A.

Age 22(4): 181-186

1999


Growth hormone (GH) stimulates metabolic activity. The purpose of this study was to examine whether it is involved in the aging process by increasing oxidative stress. Inorganic peroxides and lipid peroxides were measured in kidney and liver samples in dwarf mice that are deficient in GH, prolactin and thyrotropin and in transgenic mice that produce high levels of GH. In normal male mice, there was an increase in inorganic peroxides in the kidney with age. Levels were lower in old male dwarfs when compared with normal male mice of similar age. Unexpectedly, concentrations of inorganic peroxides were frequently lower in transgenic male and female mice expressing extra copies of GH than in normal controls. Lipid peroxide concentrations were more variable. Transgenic animals expressing bovine GH had the highest levels of lipid peroxides. In dwarfs, kidney levels were similar to those of normal mice but concentrations in the liver were more variable. This study does not indicate that the decrease in life span in transgenic mice producing high levels of GH is due to an increase of oxidative stress. Rather, it suggests that expression of extra copies of the GH gene may lead to a compensatory increase in antioxidant protection.

Age,
Vol.
22,
181-186,
1999
OXIDATIVE
STRESS
IN
HYPOPITUITARY
DWARF
MICE
AND
IN
TRANSGENIC
MICE
OVEREXPRESSING
HUMAN
AND
BOVINE
GH
J.C.
Carlson'*,
R.
Bharadwar,
and
A.
Bartke
2
1
Biology
Department,
University
of
Waterloo
Waterloo,
Ontario,
Canada
N2L
3G1.
2
Department
of
Physiology
Southern
Illinois
University
School
of
Medicine,
Carbondale,
IL
62901-
6512.
ABSTRACT
Growth
hormone
(GH)
stimulates
metabolic
activity.
The
purpose
of
this
study
was
to
examine
whether
it
is
involved
in
the
aging
process
by
increasing
oxida-
tive
stress.
Inorganic
peroxides
and
lipid
peroxides
were
measured
in
kidney
and
liver
samples
in
dwarf
mice
that
are
deficient
in
GH,
prolactin
and
thyrotro-
pin
and
in
transgenic
mice
that
produce
high
levels
of
GH.
In
normal
male
mice,
there
was
an
increase
in
inorganic
peroxides
in
the
kidney
with
age.
Levels
were
lower
in
old
male
dwarfs
when
compared
with
normal
male
mice
of
similar
age.
Unexpectedly,
concentrations
of
inorganic
peroxides
were
fre-
quently
lower
in
transgenic
male
and
female
mice
expressing
extra
copies
of
GH
than
in
normal
con-
trols.
Lipid
peroxide
concentrations
were
more
vari-
able.
Transgenic
animals
expressing
bovine
GH
had
the
highest
levels
of
lipid
peroxides.
In
dwarfs,
kidney
levels
were
similar
to
those
of
normal
mice
but
concentrations
in
the
liver
were
more
variable.
This
study
does
not
indicate
that
the
decrease
in
life
span
in
transgenic
mice
producing
high
levels
of
GH
is
due
to
an
increase
of
oxidative
stress.
Rather,
it
suggests
that
expression
of
extra
copies
of
the
GH
gene
may
lead
to
a
compensatory
increase
in
anti-
oxidant
protection.
INTRODUCTION
Growth
Hormone:
Growth
hormone
(GH)
is
named
for
its
ability
to
stimulate
growth
of
the
skeletal
system.
However,
it
is
also
an
important
metabolic
hormone
and
its
effects
are
wide
spread.
As
an
anabolic
hormone,
GH
promotes
incorporation
of
amino
acids
during
protein
synthesis
(Scanes,
1995).
It
also
affects
additional
meta-
bolic
processes.
For
example,
GH
induces
mobilization
of
lipids
from
adipose
tissue
and
increases
blood
glu-
cose
levels.
The
latter
is
known
as
an
anti-insulin
or
diabetogenic
effect
(Scanes,
1995).
Many
of
the
re-
sponses
to
GH
are
mediated
indirectly
through
the
release
of
somatomedin,
also
known
as
insulin-like
growth
factor-I
(IGF-1),
which
is
stimulated
by
GH.
Changes
in
GH
secretion and
oxidative
stress
occur
during
the
aging
process.
A
key
question
is
whether
or
not
GH,
with
its
important
effects
on
metabolic
pro-
cesses,
plays
a
role
in
the
changes
that
lead
to
oxidative
stress
and
cellular
breakdown
during
the
aging
process.
*To
whom
all
correspondence
should
be
addressed
Free
radicals
and
Peroxides:
There
is
evidence
that
the
process
of
aging
is
caused
by
the
damage
produced
by
free
radicals
during
aerobic
metabolism
(Harman
1981).
Free
radicals
are
chemicals
that
have
one
or
more
unpaired
electrons,
and
they
are
destructive.
Most
are
formed
in
mitochondria
during
respiration.
Free
radicals
can
damage
proteins
and
other
macromolecules
that
are
critical
to
cell
function.
Although
these
agents
are
produced
continuously,
antioxidant
enzymes
provide
a
mechanism
for
their
removal.
For
example,
the
superox-
ide
radical,
which
is
formed
by
one-electron
reduction
of
oxygen,
is
metabolized
by
superoxide
dismutase
(SOD)
to
H
2
0
2
and
oxygen.
Catalase
and
glutathione
peroxi-
dase
convert
H
2
0
2
to
H
2
O
(Yu,
1994).
Normally,
produc-
tion
of
free
radicals
is
balanced
by
removal,
but
as
individuals
age
homeostatic
control
declines
and
radi-
cals
accumulate,
a
condition
known
as
oxidative
stress.
Cellular
damage
associated
with
aging
has
been
re-
ported
(Sawada
et
al.,
1992).
For
example,
lipid
perox-
ides
(LP),
which
form
as
a
result
of
free
radical
attack
of
membrane
phospholipids
(Halliwell
and
Gutteridge,
1984),
increase
as
animals
age
(Shi
et
al.,
1994).
Such
alterations
may
affect
the
membrane
environment
and
disrupt
protein
function.
Oxidative
stress
can
also
be
determined
by
measuring
inorganic
peroxide
(e.g.
H
2
0
2
).
Higher
levels
correlate
with
damage
to
proteins
and
other
macromolecules.
Transgenic
Mice:
The
effects
of
chronic
elevations
of
GH
have
been
studied
in
transgenic
mice.
Constructs
of
different
promoters
and
the
GH
gene
from
different
species
have
been
used.
Foreign
GH
is
produced
in
different
organs,
such
as
the
liver
and
kidney
(Palmiter
et
al.,
1982;
McGrane
et
al.,
1988).
Circulating
GH
levels
are
variable,
but
occasionally
plasma
concentrations
are
very
high,
100
fold
or
more
compared
to
normal
animals
(Palmiter
et
al.,
1982,
Steger
et
al.,
1993).
Although
they
are
much
larger
than
normal
mice,
transgenic
mice
also
manifest
other
differences.
For
example,
life
span
is
reduced
to
half
that
of
normal
mice
(Rollo
et
al.,
1996)
but
this
also
varies
(Cecim
et
al.,
1994).
Transgenic
mice
may
also
experience
changes
in
the
secretion
of
other
pituitary
hormones.
Steger
et
al.,
(1994)
indicate
that
in
mice
expressing
bGH
(bovine
GH),
levels
of
the
pituitary
hormones
FSH
and
LH
are
depressed
but
that
PRL
secretion
is
somewhat
el-
evated.
Also,
the
GH
produced
in
mice
transgenic
with
the
human
form
will
bind
to
both
GH
and
prolactin
receptors
(Tsushima
and
Friesen,
1973).
This
latter
181
group
of
mice
also
shows
a
substantial
increase
in
mammary
tumors
not
found
in
transgenic
mice
with
the
bGH
gene
(Cecim
et
al.,
1994).
Previously
we
measured
levels
of
the
superoxide
radical
(SOR)
and
LP
in
transgenic
mice
producing
high
levels
of
rat
GH
(Rollo
et
al.,
1996).
We
observed
higher
concentrations
of
these
products
than
in
normal
mice.
The
life
span
of
the
transgenic
mice
in
the
study
was
also
reduced
to
half
that
of
normal
animals
(Kajiura
and
Rollo,
1994).
Although
it
is
uncertain
how
extra
GH
may
increase
oxidative
stress,
high
levels
appear
to
reduce
the
influence
of
insulin
on
glucose
uptake
in
adipose
tissue
at
a
site
down
stream
from
the
insulin
receptor.
There
is
evidence,
for
example,
that
GH
decreases
the
synthesis
of
glut
1,
a
glucose
transporter
(Scanes,
1995).
In
diabetes,
hyperglycemia
is
linked
to
an
in-
crease
in
oxygen
radicals
and
related
compounds
(H
2
0
2
)
and
to
protein
glycosylation
(Wolff
et
al.,
1987;
Hunt
et
al.,
1988;
Williamson
et
al.,
1993).
In
cells
in
which
glucose
levels
are
elevated
there
is
an
increase
in
the
NADH/NAD'
ratio
causing
a
redox
imbalance.
This
disturbance
can
disrupt
many
metabolic
pathways,
some
of
which
lead
to
an
increase
in
production
of
oxygen
radicals,
ROS
and
lipid
peroxides
(Williamson
et
al.,
1993).
The
result
is
an
increase
in
tissue
damage.
The
kidney
is
one
of
the
target
organs
affected
by
oxidative
stress
in
diabetes
(Beyer-Mears
et
al.,
1984;
Bell
et
al.,
1999).
Dwarf
Mice:
The
effects
of
insufficient
GH
can
be
studied
in
dwarf
animals.
Ames
dwarf
mice
are
deficient
in
this
hormone
(Bartke,
1979).
They
lack
or
have
few
somatotrophs
in
the
pituitary
gland.
In
addition,
they
are
deficient
in
PRL
and
TSH
(
Brown-Borg
et
al.,
1996).
These
mice
are
much
smaller
when
they
reach
adult-
hood,
and
females
are
sterile
as
a
result
of
PRL
defi-
ciency
and
failure
of
the
corpus
luteum
to
produce
progesterone
for
supporting
pregnancy.
Interestingly,
Ames
dwarf
mice
live
much
longer
than
normal
mice
(Brown-Borg
et
al.,
1996).
The
purpose
of
this
study
was
to
compare
the
impact
of
high
and
low
levels
of
GH
on
oxidative
stress
in
the
mouse.
MATERIALS
AND
METHODS
Dwarf
Mice.
Ames
dwarf
mice
were
housed
under
standard
laboratory
conditions
(22
C,
12-hour
light:12
hour
dark
cycle,
and
free
access
to
food
and
water).
Dwarf
animals
are
produced
by
mating
normal
carriers
of
this
recessive
gene
in
a
random
bred
closed
colony.
They
are
deficient
in
the
cells
that
produce
GH,
PRL
and
TSH
in
the
pituitary
(Bartke
1979;
Sornson
et
al.,
1996).
IGF-1
levels
are
also
extremely
low
(Chandrashekar
and
Bartke,
1993).
Adults
are
approximately
one-third
the
size
of
normal
mice.
Transgenic
Mice.
The
founder
mice
for
this
study
were
developed
by
microinjecting
bovine
or
human
structural
GH
gene
fused
to
either
metallothionein-1
(MT)
or
phosphoenolpyruvate
(PEPCK)
promoters
into
the
male
pronucleus
of
fertilized
mouse
ova
(McGrane
et
al.,
1988;
Steger
et
al.,
1993;).
The
mice
used
in
this
study
were
derived
from
single
founder
animals.
Plasma
lev-
els
of
GH
vary
in
different
lines
but
they
are
elevated
in
the
transgenics
(Cecim
et
al
1994).
The
animals
weigh
50-100%
more
and
their
life
span
is
shorter
(length
approximately
one
year)
than
normal
mice
(Cecim
et
al.
1994;
Steger
et
al.,
1993).
In
the
lines
we
used,
transgenic
mice
with
the
MT
promoter
have
lower
levels
of
hGH
(3-
15
ng/ml
plasma),
but
they
have
elevated
IGF-I
levels.
They
are
also
larger
than
normal
mice,
and
they
live
longer
than
transgenic
mice
with
the
PEPCK
promoter.
Lipid
Peroxide
Assay.
Lipid
peroxides
were
measured
in
microsomes
prepared
from
kidney
and
liver
samples.
LP
were
determined
by
the
thiobarbituric
acid
test
(Uchiyama
and
Mihara,
1978;
Sawada
and
Carlson,
1985),
and
the
results
are
expressed
as
ng
of
malonaldehyde
per
pg
of
protein.
Microsomes
were
prepared
by
homogenizing
samples
in
0.1M
Tris/HCI
(pH
8.0)
and
centrifuging
at
17,000
g
for
30
min.
Samples
of
the
supernatant
were
read
in
a
spectrometer
at
an
absorption
wavelength
of
535
nm.
A
second
reading
at
520
nm
was
subtracted
form
the
first
in
order
to
reduce
interference
(Shi
et
al.,
1994).
The
results
were
ex-
pressed
on
the
basis
of
tissue
protein,
which
was
deter-
mined
by
the
Bradford
assay
(Bradford,
1976).
Inorganic
Peroxide
Assay.
Kidney
and
liver
samples
for
the
inorganic
peroxide
(I
P)
assay
were
prepared
as
were
the
samples
for
the
LP
assay.
The
assay
is
based
on
the
procedure
described
by
Meiattini
(1985),
which
we
have
used
(Shi
et
al.,
1994).
H
2
0
2
is
used
as
the standard,
4-
aminophenazone-chromotropic
acid
is
the
hydrogen
donor
and
absorption
is
measured
at
595
nm.
The
results
are
expressed
as
ng
H
2
0
2
per
mg
protein.
Statistics.
The
results
were
examined
for
significance
using
one-way
analysis
of
variance.
Pairwise
compari-
sons
were
performed
using
LSD.
RESULTS
The
results
show
that
IP
levels
increase
with
age
in
normal
male
mice
(Figure
1).
Levels
of
this
reactive
oxygen
species,
however,
were
much
lower
in
26-
month-old
male
dwarf
mice
than
in
comparably
aged
normal
animals.
Also,
in
age-matched
normal
and
dwarf
females,
liver
IP
were
lower
in
the
dwarf
mice
(Figure
2).
Unexpectedly,
we
found
that
IP
levels
in
transgenic
mice
were
not
higher
than
in
normal
mice.
Significantly
lower
levels
were
observed
in
male
mice
expressing
bGH
(Figure
3)
and
in
the
liver
of
female
mice
expressing
hGH
and
in
the
kidney
of
females
expressing
bGH.
(Figure
4).
The
lipid
peroxide
data
appear
in
Tables
1
and
2.
Levels
were
variable.
Concentrations
were
higher
in
the
kidney
of
male
mice
expressing
bGH
than
in
male
mice
expressing
hGH
or
dwarf
males
(Table
1).
In
females
expressing
bGH,
kidney
LP
was
higher
than
for
all
other
groups
(Table
2).
Liver
LP
levels
were
higher
in
transgenic
males
than
in
dwarfs,
and
levels
in
dwarfs
were
lower
182
C
a.
O
O
4
co
3
co
t
o
3
I.
2
10
Normal
3
Month
Normal
12
Month
Normal
Dwarf
Dwarf
22
Month
4
Mon
h
26
Month
Normal
16
Month
Mr.
0
,,
Oxidative
Stress
in
Hypopituitary
Dwarf
Mice
and
in
Transgenic
Mice
Overexpressing
Human
and
Bovine
CH
Inorganic
Peroxides
in
Kidney
and
Liver
of
Male
Mice
Inorganic
Peroxides
in
Kidney
and
Liver
of
Female
Mice
Figure
1:
Inorganic
peroxide
concentration
of
kidney
(open
bars)
and
liver
(stippled
bars)
from
normal
and
dwarf
male
mice.
H
2
0
2
levels
in
kidney
samples
of
normal
22
month
mice
were
significantly
greater
(<0.01)
than
H
2
0
2
levels
in
kidney
samples
of
each
of
the
other
groups.
Also,
H
2
0
2
in
liver
samples
of
normal
12
and
22
month
mice
were
significantly
greater
(<0.01)
than
in
liver
samples
of
dwarf
26
month
mice.
Numbers
within
the
bars
indicate
number
of
mice
examined.
Figure
2:
Inorganic
peroxide
concentration
of
kidney
(open
bars)
and
liver
(stippled
bars)
from
normal
and
dwarf
female
mice.
H
2
0
2
in
liver
samples
of
normal
18
month
mice
were
significantly
greater
(<0.05)
than
in
dwarf
19
month
mice.
Numbers
within
the
bars
indicate
number
of
mice
examined.
Inorganic
Peroxides
in
Kidney
and
Liver
of
Female
Mice
Inorganic
Peroxides
in
Kidney
and
Liver
of
Male
Mica
rn
0
2
6
0
0
.
4
0
0.
0
3
E
2
r
f
0
Normal
MT-hGH
PEPCK-bGH
Normal
PEPCK-hGH
Normal
PEPCK-bGH
12
month
12
month
12
month
5
Month
5
Month
7-9
Month
7
,9
Month
Figure
3:
Inorganic
peroxide
concentration
of
kidney
(open
bars)
and
liver
(stippled
bars)
from
normal
and
transgenic
male
mice.
H
2
0
2
levels
in
kidney
samples
from
normal
12
month
and
MT-hCG
12
month
mice
were
significantly
greater
(<0.01)
than
in
PEPCK-bGH
12
month
mice.
Also,
H
2
0
2
levels
in
liver
samples
were significantly
different
(<0.01)
in
each
of
the
three
groups.
Numbers
within
the
bars
indicate
number
of
mice
examined.
Figure
4:
Inorganic
peroxide
concentration
of
kidney
(open
bars)
and
liver
(stippled
bars)
from
normal
and
transgenic
female
mice.
In
kidney
samples
H
2
0
2
levels
in
normal
7-9
month
mice
were
significantly
greater
(<
0.01)
than
in
PEPCK-bGH
7-
9
month
mice.
In
liver
samples
H
2
0
2
levels
were significantly
greater
(<0.02)
in
normal
5
month
mice
than
in
PEPCK-hCG
5
month
mice.
Numbers
within
the
bars
indicate
number
of
mice
examined.
Table
1:
Lipid
peroxides
in
normal,
dwarf
and
transgenic
male
mice.
Table
2:
Lipid
peroxides
in
normal,
dwarf
and
transgenic
female
mice.
Kidney
Liver
Age*
Kidnev
Mean**
SE
n
Liver
n
Normal
Age*
Mean**
SE
n
Mean**
SE
n
Mean"
SE
5
0.251'
0.04
5
<0.100
0.01
5
Normal
12
0.282
1,3
0.07
4
0.455
0.16
6
7-9
0.275'
0.05
5
0.103'
0.01
5
22
0.307
13
0.19
4
0.282
0.08
5
18
0.155
1
0.07
2
0.173
12
0.01
5
Dwarf
26
0.244
1
0.05
6
<0.100
0.01
6
Dwarf
19
0.361
1
0.14
2
0.261
2
0.08
6
MT-hGH
12
0.159
1
0.05
6
0.428
0.13
6
MT-hGH
5
0.246'
0.06
5
0.121
1
0.02
5
PEPCK-bGH
12
0.436
2
.
3
0.03
13
0.406
0.04
12
PEPCK-bGH
7-9
0.429
2
0.03
5
0.100
0.02
5
*Months
-
ng
MDA/pg
protein
1-3
Kidney
values
with
different
numbers
are
significantly
different
*Months
ng
MDA/pg
protein
"Kidney
values
with
different
numbers
are
significantly
different
183
than
in
normal
young
males
(12
months).
However,
in
dwarf
females
liver
LP
were
higher
than
in
all
groups
except
the
18-month
old
normal
female
mice.
DISCUSSION
The
free
radical
hypothesis
is
one
of
the
major
hypoth-
eses
explaining
the
aging
process.
As
proposed
by
Harman
(1981),
aging
is
due
to
the
progressive
increase
in
cellular
damage
caused
by
free
radical
reactions
in
the
organism.
This
notion
is
supported
by
numerous
studies
(Pryor,
1987;
Carlson
and
Forbes,
1992;
Orr
and
Sohal,
1994).
For
example,
we
measured
progressive
increases
in
the
superoxide
radical
and
LP
in
the
brain,
heart
and
liver
of
aging
rats.
Moreover,
this
rise
was
associated
with
membrane
damage
and
loss
in
protein
synthesis
(Sawada
et
al.,
1992).
Studies
with
dwarf
and
transgenic
mice
exhibiting
extreme
levels
of
GH
in
the
circulatory
system
present
an
opportunity
to
identify
the
effects
of
large
differences
in
GH
on
changes
associated
with
free
radicals.
The
life
span
of
normal
mice
is
2-3
years
(Steger
et
al.,
1993)
and
that
of
dwarfs,
which
produce
little
or
no
GH,
is
approxi-
mately
one
year
longer
(Brown-Borg
et
al.,
1996).
In
the
current
study,
we
observed
the
expected
age-related
increase
in
IP
in
kidney
samples
from
normal
mice.
Levels
of
IP,
however,
in
older
dwarf
mice
were
lower.
Although
we
are
uncertain
why
dwarf
animals
exhibit
greater
longevity,
it
may
be
related
to
lower
levels
of
metabolic
activity
(Bartke
et
al.,
1998;
Hunter
et
al.,
1999)
that
result
in
reduced
oxidative
stress.
This
may
be
interpreted
as
indicating
that
GH,
due
to
its
stimula-
tion
of
metabolic
processes,
is
involved
the
aging
pro-
cess.
However,
as
noted,
Ames
dwarf
mice
are
also
deficient
in
PRL
and
TSH
(Brown-Borg
et
al.,
1996).
Although
the
relative
impact
of
deficiencies
of
each
of
these
three
pituitary
hormones
is
unknown,
it
seems
that
the
greater
longevity
of
the
dwarfs
in
comparison
with
normal
sibling
mice
may
be
linked
to
reduced
generation
of
free
radicals,
as
indicated
by
the
free
radical
theory.
Previous
studies
with
transgenic
mice
expressing
the
GH
gene
indicate
that
they
grow
more
rapidly
than
normal
mice
and
that
their
life
span
is
roughly
one
year
(Steger
et
al.,
1993;
Kajiura
and
Rollo,
1994).
High
levels
of
GH
in
the
circulatory
system
of
transgenic
mice
have
been
confirmed
(Cecim
et
al.,
1994).
Studies
with
mice
expressing
the
rat
GH
gene
also
reveal
higher
levels
of
SOR
and
LP
in
plasma
membrane
samples
from
kidney
and
liver
than
in
samples
from
normal
mice
(Rollo
et
al.,
1996).
A
higher
level
of
oxidative
stress
and
consequent
damage,
as
evidenced
by
greater
lipid
peroxidation,
may
be
causally
related
to
the
reduction
of
life
span.
In
contrast
to
the
transgenic
mice
expressing
rat
GH,
the
transgenics
in
the
present
study
were
derived
from
founder
male
mice
expressing
human
or
bovine
GH.
These
mice
produce
a
wide
range
of
heterologous
GH,
which
is
also
associated
with
reduced
life
span
(Cecim
et
al.,
1994).
In
the
present
study,
however,
the
expected
correlation
between
expression
of
GH
in
transgenic
mice
and
high
levels
of
inorganic
peroxides
in
kidney
and
liver
samples
did
not
hold
up.
Contrary
to
the
observation
cited
above
(Rollo
et
al.,
1996),
there
was
either
no
apparent
change
in
IP
concentration
or
signifi-
cantly
less
in
transgenic
mice.
Although
the
explanation
for
this
is
uncertain,
it
seems
possible
that
there
could
be
higher
levels
of
antioxidant
activity
in
the
transgenic
animals.
Recent
studies
with
transgenic
mice
express-
ing
hGH
indicate
that
SOD
levels
in
the
hypothalamus
are
higher
than
in
normal
mice
(Hauck
and
Bartke,
1999).
Also,
in
rodents
human
GH
exhibits
the
biological
effects
of
PRL
(Tsushima
and
Friesen,
1973).
PRL
has
been
reported
to
induce
SOD
activity
in
the
rodent
corpus
luteum
(Sugino
et
al.,
1998),
an
important
target
organ
that
is
critically
dependent
upon
antioxidant
activ-
ity
for
controlling
function
(Sawada
and
Carlson,
1996).
Although
the
LP
levels
in
this
study
were
variable
(Tables
1
and
2),
we
observed
lower
levels
in
kidney
samples
of
mice
expressing
hGH
than
in
mice
expressing
bGH,
which
does
not
possess
PRL
activity.
This
may
be
related
to
differences
in
circulating
levels
of
GH
(Cecim
et
al.,
1994)
or
to
the
particular
biological
activity
asso-
ciated
with
the
type
of
GH
gene
being
expressed
in
the
transgenic
mouse.
In
general,
our
results
indicate
that
transgenic
mice
expressing
human
or
bovine
GH
do
not
show
the
anticipated
increase
in
free
radical
activity.
Although
higher
levels
of
GH
would
appear
to
elevate
oxidative
stress,
it
is
possible
that
compensatory
mecha-
nisms
such
as
increased
protection
by
antioxidant
en-
zymes
may
offset
the
expected
damage.
ABBREVIATIONS
Growth Hormone,
GH;
superoxide
dismutase,
SOD;
lipid
peroxide,
LP;
follicle
stimulating
hormone,
FSH;
luteinizing
hormone,
LH;
bGH,
bovine
growth
hormone;
superoxide
radical,
SOR;
reactive
oxygen
species,
ROS;
prolactin,
PRL;
thyroid
stimulating
hormone,
TSH;
metallothionen,
MT;
phosphoenolpyruvate,
PEPCK;
human
growth
hormone,
hGH;
inorganic peroxides,
IP;
least
significant
difference,
LSD.
ACKNOWLEDGMENTS
This
study
was
supported
by
the
National
Science
and
Engineering
Research
council
of
Canada.
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