BIOLOGY
OF
REPRODUCTION
Prenatal
389-396
47,
Androgens
(1992)
and the Timing
RUTH
Reproductive
Sciences
Program,
of Seasonal
I. WOOD3’4
and
and
Departments
University
Reproductive
DOUGLAS
Ann
in Sheep1
L. FOSTER2’5’6
of Physiology,4
of Michigan,
Transitions
Arbor,
Obstetrics
Michigan
and
Gynecology,5
and
Biology6
48109-0404
ABSTRACT
the
Both
are
of puberty
onset
by
characterized
is
puberty
remain
present
study
and
compared
We
females.
UI
a reduction
in sensitivity
inhibition
until
30 wk.
This
whether
a sex
difference
females
(n = 5) from blood samples
collected
twice
the onset and termination
of the autumn
breeding
(termination:
1 February
androgenized
females,
but
not
in females
or
secretion
in adult
in 3 of 5 animals,
data
These
activity
4 days,
±
mean
16 September
±
10.5
androgenized
females.
suggest
sex
that
in gonad-intact
differences
male
groups;
However,
onset:
effects
However,
cies
in a long-lived,
such
as the
of sexual
activity
signals
breeding
(for
sheep
and
anovulatory;
increases
fertility
established
by increased
to inhibitory
females
of
tive activity
at the
recurrent
puberty.
In the
tiated,
lamb,
as males
feedback
responsive
October
‘This
work
was
HD-18258,
President
from
the
and
the
as a result
feedback
general
mechanism
also
at puberty
in the
of the
the
season
of puberty
drives
lamb
for
by research
and
Research
at the
University
of Michigan
at the 21st Annual
Meeting
USDA
and
training
grants
(89-37240-4561),
chased
land,
University
(R1.W.).
of Michigan,
Preliminary
of the Society
and
reports
for
from
the
NIH
Support
a Regent’s
of this work
Neuroscience,
New
versity
of Michigan,
5Current
Building,
address:
University
Douglas
Ann
Arbor,
Department
of Michigan,
L Foster,
Room
MI 48109-0404.
of Anatomy
Ann
Arbor,
1101,
FAX:
and
300
(313)
Cell
N. Ingalls
Medical
male
and
in
control
males,
of UI
differences
in sexual
by androgens
in utero.
female
androgenized
first
into
male
breeding
the
sheep,
to prenatal
of circulating
start
and
if so, whether
androgen
exposure.
LH in postpubertal
and
female
season,
of the
AND
Building,
Sciences
previous
transported
Sheep
Research
sheep
through
second
from
seasonal
breeding
season.
METhODS
pre-
effects
LA,
UniII
MI 48109-0616.
389
lambs
of
year
to
(n = 7 and 6, respec11 April
± 2 were
pur-
from
the
Facility
Breasbois
Reproductive
in Ann
Farms,
Arbor
FreeSciences
(42#{176}
18’
male and female
research
facility
(12
were
masculinized
N)
lambs
April
by
(n
±
2
expo-
to testosterone
cypionate
via maternal
injection
each
during
midgestation,
as previously
described
[9]. The
genitalia
masculinized;
24 lambs
Fellowship
were
Suffolk
birthdate
in the
MI, and
external
(HDto the
Orleans,
female
a mean
wk of age. Androgenized
=
5 each) were born at our
days birthdate).
These
lambs
936-8620.
Biology,
to sex
at one
1991.
‘Correspondence:
18 days;
±
throughout
the nonbreeding
season
in responsiveness
to steroid
inhibition.
contribute
their
and
Program
to steroid
Biomedical
androgenized
in the
to be determined
and
of
Male and
tively)
with
4, 1991.
HD-18394)
males
Animals
sure
week
supported
and
The
adult
to 23 June)
May
evident
MATERIALS
differen-
in sensitivity
in utero.
in
5 September
(20
UI
are due
the patterns
female,
end
anestrous,
resembles
is sexually
a reduction
6),
=
of
whereas
is
of reproduc-
breeding
age,
13, 4]
males
resumption
(n
were
in adult
of reduced
in both
activity
annual
timing
season
may
do not appear
male,
females
breeding
of
transitions
females,
In
elevated
such
differences
We compared
7, 1992.
Received
sented
the
male,
4 days;
increases
transitions
at 10 wk of age, whereas
females
remain
highly
to steroid
inhibition
until
30 wks [8]. This sex
May
Vice
start
undergo
Accepted
07048,
into
LH secretion
the
period
photoperiod
the breeding
season,
sperrecurrent
ovarian
cycles
be-
steroid
manner,
by
in the
during
and
[5]. This same
reproductive
[6, 7]. In this
is timed
wk
sheep
timing
difference
is determined
by androgens
in utero
[9]. The
present
study was conducted
to determine
whether
similar
sex differences
exist in the timing
of seasonal
reproductive
spe-
et al. [1]). During
the nonSuffolk
sheep,
testis size is
[1, 21. Entry
response
onset
Karsch
mature
breeding
by a discrete
that
decreases
governed
and
the
year
review,
see
season
of the
reduced
come
is characterized
each
become
matogenesis
seasonally
±
was
10
by androgens
females
increase
ftinction
such differences
7),
testosterone
males
seasonal
at
of seasonal
=
female
the
by changes
in the pattern
of LH secretion,
males, females,
and androgenized
females
22 August
neuroendocrine
INTRODUCTION
Reproduction
(n
a transient
of prenatal
feedback
timing
and
male
However,
is determined
the
in
males
males,
secretion
in androgenized
testosterone
may reduce
sheep.
difference
sex
exists
there was
no
Although
in reproductive
female
and
season
in adult
inhibition.
steroid
for one year.
As detertnined
were
not different
between
days).
androgenized
females,
UI
indicating
that exogenous
to
estradiol-treated
weekly
SE all
±
activity
to steroid
responsiveness
reduced
gonadectomized,
in
of reproductive
resumption
to
undergo
males
to steroid
serum
annual
due
LH
to determine
conducted
the
and
of
for
responsive
highly
was
lamb
secretion
differentiated,
sexually
females
the
in
increased
of the
androgenized
those
of the males
were
used
in an earlier
of androgens
on
the
timing
After weaning,
the
leted
diet containing
lambs
were
20% protein
tamins,
minerals,
alfalfa
growth.
Water
and
was
available
hay
females
appeared
study
were
normal.
investigating
of sexual
to maintain
Body
These
the
19].
maturity
fed a commercial
supplemented
at all times.
heavily
a rapid
weight
with
rate
pelviof
at the
390
WOOD
start of the study averaged
60.1 ± 1.9 kg, within
range
for adult sheep
at our facility.
The lambs
housed
outdoors
under
natural
photoperiod
first
year
of life
and
for
the
duration
of the
AND
the normal
were groupduring
their
study.
FOSTER
Evaluation
mined
Gonadectomy
To
and
and
Steroid
standardize
the
androgenized
moved
and
plant
hormonal
steroids
to provide
diol was used
have a similar
milieu
and
replaced
a constant
steroid
in both
degree
to the
estradiol
important
role
in inhibitory
[10]. At 2 wk of age, control
der
were
ovariectomized
Following
a small
an
im-
signal.
Estra-
drogenized
because
to estradiol
males
and
pling
feedback
in the
and androgenized
midventral
ram
fe-
laparotomy
to
un-
remove
inhibi-
males
and
at 2 wk of age.
each
lamb
was
implanted
(o.d.
0.46
cm,
id.
s.c. with
0.34
cm,
Dow
Corning,
Midland,
MI) containing
a 30-mm
packed
column
of crystalline
estradiol-17
(Sigma
Chemical
Co., St. Louis,
MO) and sealed
with Silastic
Adhesive
Type A (Dow
Corning).
Before
in water
steroid
implantation,
all
capsules
were
level
of approximately
3-5
pg/mi
at a
16-8].
UI Assay
LH was
measured
in duplicate
serum
using
modifications
Niswender
et al. [14]. The
standard
deviations
0.06 ng/ml
for 200
above
maximum
pA of serum
(15
respectively;
12%,
Seasonal
Changes
Beginning
season,
interassay
in Tonic
blood
samples
jugular
venipuncture
tinuous
changes
in
by
mental
vember
period.
of the
gonadectomized
centration
increase
duction
8].
LH
Biweekly
following
lamb,
responsiveness
CV averaged
(CV),
9.5%
14.9%.
LH Secretion
of the
were
sampling
year.
first
autumn
collected
In
a sustained
breeding
from
each
continued
until
the estradiol-treated
rise
in serum
infrequently
which
results
to inhibitory
by
female
period
transiently
steroid
doses
lamb
6 No-
that
lambs
for tonic
increasing
ples were
collected
period
was necessary
the
do
not
UI
U-I surge
at the
start
secretion;
estradiol
exert
a
secretion
of LH in the
female
before
puwas
blocked
and
end
in mastudy,
and an-
of the
this was accomplished
in mid-January,
near
delayed
Data
in the
every
2 h for 72 h; the
in the event
that the
androgenized
samthe
females
long sampling
UI surge
was
[15-17].
Analysis
samples
mination
drogenized
laboratory
ceeding
productive
samples
activity.
collected
biweekly
to specify
the onset
and
of reproductive
activity
in males,
females,
and
females.
According
to criteria
established
in
[21], the first of six consecutive
UI samples
1 ng/ml
marks
the onset
of “neuroendocrine
activity.”
Conversely,
the last of six consecutive
above
On the
1 ng/ml
signifies
the
basis of these
criteria,
[6-
end of reproductive
neuroendocrine
teranour
exre-
re-
productive
activity
in gonadectomized
lambs
bearing
an
implant
of estradiol
coincides
with ovarian
cycles
or spermatogenesis
in gonad-intact
males
and females
[8, 21].
UI surge identftcation.
UI surges
induced
by increasing circulating
estradiol
were
identified
using
the criteria
of Legan
et al. [22,23].
According
to this method,
UI levels
must be sustained
above
5 ng/ml
for at least 8 h.
Analyses
The
timing
of seasonal
reproductive
transitions
was
compared
in males,
females,
and androgenized
females
by
analysis
of variance
(ANOVA).
The timing
and amplitude
of
the UI surge
were
also compared
by ANOVA.
Values
below
assay sensitivity
were
assigned
the limit of sensitivity
of the
assay.
LH conreflects
an
from
a re-
feedback
of estradiol
end of the first breeding
season,
and again
11 months
later
in mid-December,
during
the second
breeding
season.
To
facilitate
high amplitude
UI surges,
estradiol
capsules
were
removed
for three
weeks
before
UI surge
induction
[18].
All lambs
were
treated
with four 30-mm
implants
of estradioi to raise serum
concentrations
to approximately
12 pg/
ml, comparable
to levels
during
the late follicular
phase
[19,20].
To monitor
UI during
surge
induction,
blood
sam-
Statistical
twice
each week
to monitor
consecretion
throughout
the experi-
from
samples
collected
in LH pulse
frequency,
in
of
binding,
was 0.65 ±
assays),
expressed
rel-
coefficients
of variation
control
pools,
averaged
on 23 November
5-mi
aliquots
[12, 13] of an RIA developed
by
mean
sensitivity,
defined
as two
ative to NIH-LH-S12.
Intraassay
determined
from two quality
and
25- to 200-pi
physiologic
Biweekly
samples for UI and the timing
of neuroendocrine reproductive
activity.
We used the pattern
of UI from
preincubated
for 16-18
h to prevent
a peak in postimplantation
release
[11]. This implant
maintains
estradiol
constant
Mechanism
ture males
and androgenized
females
in the present
we attempted
to induce
surges
in males,
females,
lambs
anesthesia
capsule
estradiol
Surge
feedback
effect
on the
[18] or in the androgenized
[9]. To confirm
berty
re-
regulation
of LH pulse
freis considered
to serve an
via
gonadectomy,
were
feedback
steroid
feedback.
Control
males
were
orchidectomized
Silastic
females,
gonads
with
steroid
females
acepromazine/ketamine
tory
gonadal
androgenized
the
male and female
of responsiveness
testosterone
with regard
quency
[7], and because
males
in males,
females,
were
that
stimulatory
adult
ram
Replacement
males
of the Gonadotropin
Short
[15] and Clarke
et al. [16, 17] initially
reported
that
androgenized
females
fail to produce
an U-I surge
as adults
in response
to exogenous
estradiol.
We have also deter-
RESULTS
Seasonal
Males
UI
secretion
Changes
in Reproductive
and fenales.
Figure
over
the
50-wk
Activity
1 presents
experimental
the patterns
of
period
in two
DIFFERENCES
SEX
IN
FEMALES
100
There
was considerable
variation
within
onset
of the autumn
breeding
season.
In
creased
September
breeding
remaining
10
.1
:
917
391
REPRODUCTION
SEASONAL
in UI
on
C)
secretion.
end of the
the autumn
C
I
in males
-J
the
917
in the
UI in-
5 September
± 18 days
(range,
May [n = 1] to
[n = 5]). In five of seven
males,
the autumn
season
began
on 22 August
± 4 days.
The two
males
did not exhibit
normal
seasonal
variations
Circulating
bottom)
remained
riod. In a second
E
groups
females,
springtime
breeding
and
in one
male
(#914,
Fig.
the experimental
did not decrease
was
not
compared
of variability.
difference
in tonic
UI
due
secretion
occurred
crease
in UI. In the five males
displaying
a seasonal
rhythm
of UI secretion,
UI concentrations
rose on 20 May and remained
elevated
for an average
of 5 wk until
23 June.
UI
was consistently
elevated
throughout
this period
in the remaining
two
ments
males.
above
The
1 ng/mi
exhibited
to
921
92
males
statistically
during
921
when
through
season
911
92
spring,
1,
peat the
rise, but remained
elevated
season.
Onset
of the breeding
females
high degree
The sole sex
the
UI
high
throughout
male (#916),
UI
number
a transient
of biweekly
averaged
14
UI
measure-
1.1 during
±
in-
this
month
period.
In females,
UI remained
consistently
1 ng/ml
in five animals.
In the remaining
female,
creased
on May 27 and remained
elevated
into the
two-
below
UI insecond
autumn
breeding
season.
Nonetheless,
concentrations
of UI
in biweekly
samples
exceeded
1 ng/ml
on an average
of
2.8
2.4 occasions
±
Androgen
E
each of the
2 in relation
0)
C
(bottom).
I
The
end
of the
females
16 September
that of normal
natal exposure
failed
to
MAR
MAY
JUL
SEP
FIG. 1. Profiles
of LH secretion
on a logarithmic
scale in two female
and male (bottom)
yearling
lambs from samples obtained twice
weekly.
Dotted
line indicates
sustained
increase
in LH above 1-ng/ml
limit to define
neuroendocrine
reproductive
activity.
Shaded
areas represent
the periods
of elevated
LH secretion
for each individual.
Bars (below)
represent
periods
of elevated
LH secretion
for each individual
in the group.
(top)
was
not
male lambs;
also shown
in all animals
in each
of the study
in late
in both
males
and
collected
3 February
± SE).
twice
±
Thereafter
November,
females,
per wk. Mean
6 days;
females,
in females,
are the periods
of
group.
At the start
UI secretion
as determined
was
from
elevated
samples
UI fell in midwinter
(males,
21 January
± 4 days;
mean
UI
remained
below
1 ng/ml.
the
adult
not
breeding
different
10.5
was
not
transient
other
of normal
31 January
breeding
different
from
despite
prefemale
lambs
springtime
androgenized
increase
females
for
in these
that
decreased
on
of the autumn
days,
June.
in Figure
and female
season
from
of normal
males.
One
heavily
tended
to increase
UI at that
sustained;
and
secretion
females
is depicted
for a male (top)
secretion
the start
±
of May
of UI
in
LH
masculinized
time, but this
showed
some
evidence
of this phenomenon
to varying
degrees.
However,
the average
number
of biweekly
samples
above
1 ng/ml
(2.8 ± 1.2 points)
was not different
from
that of normal
(p >
Androgenized
females
neuroendocrine
female
and two
high UI secretion
pattern
males
and females.
Importantly,
to testosterone,
androgenized
exhibit
characteristic
female
(#913)
JAN
months
The
first
was
males
and females;
UI
± 5.5 days.
In addition,
season,
the
five androgenized
to typical
profiles
androgenized
-J
during
ized females.
posed
ment.
genized
group.
three
of the
either
riod
to
On
0.05).
males.
Figure
3 illustrates
activity
in yearling
sexual
exogenous
the left are
males
On the
patterns
androgens
profiles
depicting
right
are
the
the
during
of UI from
the timing
male
lambs
prenatal
individual
of
ex-
developandro-
three
patterns
typical
of this
relative
frequencies
of these
in androgenized
and
normal
males.
Like
those
normal
males,
the UI profiles
of androgenized
males
were
nonseasonal
(60%),
possessed
only a brief pe-
of inactivity
(20%),
or
had
two
distinct
periods
of el-
392
AND
WOOD
FOSTER
was
much
less
so. In the
of adult
sexual
activity
the timing
of puberty
tober
± 4.5 days, p
increase
in UI at the
(16
pared
September
to the
A similar
male.
In
I
this
a majority
the
UI
a month
season
was
observed
rise
at puberty
before
the
(22 August
males,
it is not
rise in the lamb
of these
changes
the
seasonal
18 days)
female
In androgenized
of breeding
season
relationship
the androgenized
timing
of the UI
female,
onset
preceded
(16 Oc-
females,
the
as yearlings
days) was delayed
significantly
comrise in UI (16 July ± 20 days, p <
group,
9.3 days,
breeding
±
start
pubertal
0.05).
June
autumn
0.05).
<
10.5
±
normal
(5 September
±
in the spring-born
males
in LU secretion
failed
in the
normal
began
on
19
increase
in LU at the
4 days).
Finally,
in
±
possible
to compare
the
and in the adult because
to show
normal
seasonal
as adults.
UI Surge
first
Individual
patterns
of UI secretion
for 72 h during
the
and second
breeding
seasons
in response
to an abrupt
increase
in estradiol
androgenized
from these
ing
in representative
males,
females
are depicted
three
groups
is presented
estradiol
to
levels
females,
in Figure
in Figure
approximating
the
and
5. Mean
UI
6. Increas-
follicular
phase
initially
suppressed
UI secretion
in all three groups.
In normal female
lambs,
this was followed
by a surge
of UI 13.7
± 0.6 h later
that peaked
at 95.1 ± 10.5 ng/ml
of UI 18.3
± 0.6 h after
estradiol
treatment.
Increased
also
JAN
MAR
MAY
JUL
SEP
during
FIG. 2. Diagrammatic
sagittal
section
through
the hindquarters
of a
normal
male (top), normal female
(bottom),
and each androgenized
female
lamb (middle)
in descending
order of masculinization;
penis and scrotum
are shaded.
Right: Profiles
of LH secretion
on a logarithmic
scale in gonadectomized,
estradiol-treated lambs from samples collected twice weekly.
Top: LH in a representative
control male. Dotted
line indicates 1-ng/ml limit
to define neuroendocrine
reproductive
activity.
Bottom:
LH in a representative control female.
Middle:
Individual
LH profiles
for five androgenized
females
in descending
order
of masculinization.
Shaded
areas represent
the periods
of elevated
LH secretion
for each individual.
males,
UI secretion
present
in
the
the
first
UI
following
androgenized
surge
increase
induction.
was
estradiol
females
In
delayed
treatment
and
the
relative
normal
androgenized
to that
was
males
fein nor-
CI)
w
-J
evated
trast,
UI
separated
a distinct
by basal
biphasic
of normal
males,
and
males were nonseasonal
Puberty
Figure
sexual
Versus
with
of UI
present
in 70%
was
U0
smaller
percentages
of normal
(15%)
or only partly seasonal
(15%).
the
Season
sustained
determined
puberty
In con-
pattern
laboratory
[9], with the rise
of the adult
breeding
season
lings.
The timing
of puberty
entiated,
(20%).
much
the Breeding
4 compares
maturity,
LU secretion
earlier
in UI
study
secretion
from
at
our
in circulating
UI at the onset
in these
same
lambs
as yearwas markedly
sexually
differ-
in males
occurring
some
15 wk before
start of the breeding
season
rise
in an
and
androgenized
females
that of females.
However,
the
in the same
groups
as adults
JAN
MAR
MAY
JUL
FIG. 3. Left: Profiles of UI secretion
in three yearling male lambs treated
prenatally with androgens
illustrating the range of reproductive responses
in this group of sheep. Dotted
line indicates
1-ng/ml
limit to define neuroendocrine
reproductive
activity.
Shaded
areas represent
the periods
of
elevated LH secretion for each individual. Right: Incidence
of cyclic and
aseasonal
patterns
of LH secretion
in androgenized
(dark bars) and normal
(light bars) male lambs.
SEX
DIFFERENCES
SEASONAL
IN
puberty
breeding seasons
0
REPRODUCTION
curred
393
in response
to estradiol
drogenized
females.
The overall
differences
males,
and males
in UI
estradiol
are
treatment
in males
females,
after
androgenized
acute
increases
among
secretion
exemplified
in Figure
of UI in females
decreased
treatment,
but then were
treatment
baseline
during
6. Mean
anfein
concentrations
in the first 12 h after
elevated
2-3-fold
over
the next 12 h. In males
drogenized
females,
UI was initially
mental
estradiol.
Subsequently,
UI
exceed
baseline
UI concentrations.
or
suppressed
increased,
estradiol
the preand an-
by supplebut did not
DISCUSSION
The
present
study
describes
the
pattern
of tonic
cretion
in gonadectomized,
estradiol-treated
male lambs,
and in androgenized
males and
their
was
second
used
year
to
of life.
determine
This
whether
roendocrine
activity
underlies
ductive
function
in gonad-intact
MAY
JL..
of LU concentrations,
male
females
steroid-clamped
a sex
lamb
difference
the sex difference
male and female
the
basis
tive
and
activity decreases
at the same time of year
females,
and due to individual
variability
neuroendocrine
UI
se-
and feduring
model
in neu-
in reprosheep.
On
reproducin both males
the onset
of
,JL.AU
FIG. 4. Comparison
of the timing
of puberty
(open circles) and entry
into the breeding
season
(dark circles) in females
(top), androgenized
females (upper middle),
males (lower middle),
and androgenized
male lambs
(bottom) during the firstand second year of life. The mean ± SE for each
group are depicted in the shaded boxes. Neuroendocrine
reproductive activity was defined
in gonadectomized,
tained
increase
in LH secretion.
mal
ng/ml
females,
tion
in the
5.6
h after
comparable
5.2 ng/ml).
tained
reaching
at 30.8
±
2.5
males
estradiol
to that
During
elevations
estradiol-treated
peak
concentrations
h after
increased
estradiol
even
treatment),
above
as a sus-
of 32.7
treatment.
later
(peak
with
a mean
of the androgenized
the second
surge
in UI
lambs
pretreatment
10.7
±
UI
secre-
height:
43
±
amplitude
females
induction,
(35.3
±
no sus-
baseline
oc-
FIG. 5. LH response
to follicular
phase levels of estradiol
in two representative
a gonadal
female
(left), male (right), and androgenized
female
lambs (middle). Surges were induced at 10 mo of age in January (top) and
again at 21 mo of age in December
(bottom)
by insertion
of estradiol
capsules to raise circulating
concentrations
to approximately
12 pg/mI.
Blood
samples
were collected every 2 h for 72 h.
FEMALES
ANDRO(3ENIZED
394
FEM4LES
? ape
10 months
WOOD
AND
FOSTER
tribute
MALES
‘‘‘‘‘‘ft’,,’.’
40
30
gests
E 10
aae
-J
40
20
]D
1424
--0
3848
6272
‘
‘
‘
--O
‘
TIME (hours)
1424
3848
from that
a unique
tonic
UI
posed
drogen
UI,
breeding
season
in the
male
is not
different
in the female.
However,
the adult male possesses
springtime
increase
in UI. This sex difference
in
secretion
was not masculinized
in females
ex-
to androgens
in the male
for the
in utero.
However,
supplemental
did influence
the circannual
pattern
majority
of prenatally
the normal
seasonal
addition
to examining
fluctuations
tonic
phasic
release
pattern
of UI
in circulating
estradiol.
androgenized
males
anof
lacked
in reproductive
activity.
UI, we also determined
males,
these
but
results
in the
these
are
lamb
in response
Females
to acute
produced
observations
compared
during
increases
early
were
with
not
those
repeatable.
of our
prepubertal
earlier
development
could
is markedly
By contrast,
females
February
to August
different
from
that
apsex
difference
in males
and females
could
reflect
simply
gonadal
differences
in continuous
(male)
versus
cyclic
male)
production
of gametes.
Alternatively,
prolonged
the
(fere-
function
driving
in gonadectomized,
veal
a sex
in the
difference
male
sheep
could
in reproductive
be
due
to an
neuroendocrine
earlier
in tonic
UI
secretion
that
could
con-
for the
study
sexually
differen-
the
spring
and
not prevent
male feras a continuum
from
fertility
[2]. Thus,
on the
By contrast,
the
male’s
reproduc-
is an all-or-nothing
event
in the seasonal
pattern
of
determined
in the present
to differences
and
in the
seasonal
females.
study
of the present
to masculinize
tonic
using
females
However,
autumn
breeding
season
androgenized
as adults
according
none
springtime
tonic
LU
amount
opment
females
activity
in
[4,25,26].
Our
determined
that
of the
UI increase.
secretion
in
would
follow
that of the normal
to our criteria
for elevated
UI
androgenized
females
It may be that
the adult
male
or duration
of androgen
than we provided.
Our
ceived
middle
androgen
reproductive
exposure
androgenized
female
pattern
Comparing
with
those
exposure,
of UI secretion.
the results
of our
of the
present
system
study
study
a
during
develfemales
re-
only
in the
postpubertal
neuroendocrine
sustained
masculinization
of
requires
a greater
testosterone
via maternal
injection
third
of gestation.
Alternatively,
continued
berty
increase
in reproductive
to increase
spermatogenesis
could
be advanced
by exposure
to androgens
pre[9]. On the basis of those earlier
results,
we anticithat the pattern
of tonic
UI secretion
in the andro-
secretion,
the
gametogenesis.
Results
of the present
study
estradiol-treated
males
and females
re-
difference
sea-
secretion
inhibits
follicular
ovulation
[see 24]. This could
a restricted
breeding
season
of mating
throughout
the year.
in males
preparation
it
do
exists
female
contribute
of reproduction
study
are anovulatory
from
of each year [1]. This
activity
providing
This sug-
breeding
during
to full
in the
pothesized
that this brief
in the male
is important
[9],
but
sex differences
which
were
not
also
be
photoperiod
is minimal.
When
males.
sex
repro-
UI secretion
in females
androgenized
in utero.
In males,
the transient
springtime
elevation
in LH pulse
frequency
has been
described
previously
in both
testes-intact
and
gonadectomized,
steroid-treated
models
[4]. It has been hy-
genized
underlying
The
enhance
of the
One of the most unexpected
findings
the inability
of prenatal
testosterone
of
sheep
cycles
In this regard,
FSH secretion,
pattern
also
to oligospermia
of ovarian
females.
Adult
males
of the Suffolk
breed
do not become
azoospermic
during
the nonbreeding
season,
although
testis size and spermatogenesis
decrease
during
the summer
productive
timing
UI pulses
Slow
frequency
gonadotropin
development
and prevents
explain
why
females
have
whereas
males
are capable
intact
months
[2].
proximately
sheep.
may
to females
by
to the testes.
may
frequency
overall
effect
of inhibitory
productive
performance
was
a preovulatory
season
slow
azoospermia
puberty
natally
pated
male
in the
summer
months
may impair
tility, because
spermatogenesis
appears
that sexual
differentiation
of UI secretion
in the
sheep
is also manifest
in adulthood.
The seasonal
pattern
of reproductive
activity
in gonadadult
LH
is insufficient
to account
completely
for sex difin the seasonal
pattern
of reproductive
activity
in
sheep.
It appears
that the response
of the ovatestes
to reduced
gonadotropin
secretion
during
The
study,
In
the
surge
characterized
by sustained
high-level
secretion
of UI.
In males
and androgenized
females,
concentrations
of UI
in serum
recovered
from
initial
suppression
by estradiol.
Occasional
increases
in UI secretion
were observed
in normal
in
relative
stimulation
differences
nonbreeding
tiated.
tion
autumn
sex
in gonad-intact
increase
in males
gonadotropin
that
the
672
FIG. 6. Mean (±SE)
LH secretion
before and after elevating
estradiol
to follicular
phase levels (-12
pg/mI)
in female
(left), male (right), and androgenized
female
lambs (middle).
Surges were induced at 10 (top) and 21
mo of age (bottom).
Note the LH surge induced
in female
lambs between
14 and 24 h.
the
differences
activity
ent study
ferences
gonad-intact
ries and
L
30
10
sex
son in the adult Suffolk
sheep
are at least partly
due to sex
differences
in reproductive
neuroendocrine
function.
The sex difference
in UI secretion
revealed
in the pres-
i.c
21 mo thtof
the
springtime
ductive
additional
20
‘I
to
transient
during
absence
the
of
maturation
may
on the
in males,
of
be toward
timing
females,
a
of puand
SEX
androgenized
may respond
female
lambs, it appears
differently
from adults
ual activity.
neuroendocrine
summer
its lowest
Young
[7-9],
ebb
that prepubertal
lambs
to cues that time sex-
males
and androgenized
sexual
maturation
during
when
UI secretion
[4]. In contrast,
the
the
In
the
is not. This suggests
activity
is changing
sheep,
females
long
in the adult
young
female
berty
some
four to six weeks
after the adult
the breeding
season
[6]. Although
the timing
markedly
sexually
differentiated,
with as many
separating
the pubertal
UI rise in male
and
[8,9], entry
into the autumn
breeding
season
and females
timing
sexual
lamb.
that the response
to cues
even
in the postpubertal
photoperiod
is the
principal
cue
ing
the
day
duration
[see 27,
inhibition
The
than
the
are
trast, the
the adult
day
male
adult ram,
inhibition
to steroid
males
young
males
and
females
under
after
the
activity
do suffice
prepubertal
for the adult
and adult
is not
in the
solstice
immutable,
but
males,
of the
a much
males
retained
season
(60%)
or
(20%).
individual
ductive
[9]).
variation
Previous
function
posure
to exogenous
cate that increasing
enhance
termine
natal
present
larger
in the
studies
in the
they
between
to pho-
as the
study
was
lamb
the
percentage
inin
Rel-
of our
an-
high
UI throughout
the nonexhibited
only a brief period
of
We speculate
that an even greater
male
androgens
androgens
gonadotropin
secretion.
whether
spermatogenesis
androgens,
to time
although
patterns
of UI secretion
androgens
in utero.
would
have exhibited
had they been
mascuIn this respect,
there
is
amount
of masculinization
in the offspring
in response
to the same
ment
of the mother
(e.g. external
genitalia,
in females
inadequate
changes
it
percentage
of androgenized
males
continuous
high-level
LU secretion
linized
to a greater
extent
in utero.
large
[9]. In con-
female
that
of aseasonal
to exogenous
hypogonadotropism
in response
when
young
female
[21]. This difference
sheep
suggests
that response
finding
drogenized
breeding
are
prepubertal
creased
incidence
male lambs
exposed
to normal
to photoperiod
photoperiods
matures.
An unexpected
ative
after
use melthey aptran-
appears
much
more
sensitive
than
transitions.
In this regard,
constant
summer
reproductive
toperiod
opposite
young
female
to photoperiod
lengths
less sensitive
is much
of
begins
and the pubertal
reduction
is minimally
delayed
even
reared
timing
melatonin
encodes
for length
The reduction
in responsiveness
in adult
neuroendocrine
have
may
be
androgen
pubertal
suggested
that
compromised
[29,30];
during
Although
we
is compromised
function
treatUI rise
reproby ex-
our results
development
did
is certainly
REPRODUCTION
indimay
not deby prenot
395
inhibited.
During
our earlier
study
of prepubertal
genized
lambs,
we observed
an earlier
reduction
sponsiveness
to steroid
inhibition
in males
that
androin rereceived
androgens
[9]. How-
ever,
weight
in utero
those
and
compared
results
faster
were
enhance
Nonetheless,
present
study
males
during
reproductive
ing puberty
tion.
The
and
focus
sheep.
ization
of tonic
on the
UI
studies
absent
have determined
in the normal
androgens
duction
more,
in
culinized
springtime
level
of LH secre-
the
seasonal
effects
regu-
of testosterone
females.
preovulatory
[18] and
The
Previous
UI surge
is abolished
results
study support
UI secretion
of UI
UI
female
surge
is
by
surge
this concept.
was incompletely
androgenized
absent),
the
in-
Furthermas-
did
(i.e.
the
not re-
that sexually
dimorphic
traits may vary
to the amount
or duration
of androgen
Recent
studies
that a surge
the UI surge
the UI surge
was
the
sheep
[15-17].
in utero.
demonstrated
accompanies
at the
male
in the adult
UI rise was
exposure
study
androgenized
that
present
tonic
cover,
suggesting
their
susceptibility
by advanc-
inhibition
to the
in adult
utero
in the
although
function
with
anmay
LH secretion
in adult
male and fewe also wished
to relate
masculin-
U-I secretion
surge
birth
males
that finding
coupled
suggest
that increasing
prenatal
development
seasonal
of this
pulsatile
However,
males
by the larger
androgenized
neuroendocrine
reducing
primary
of tonic
to untreated
confounded
rate of the
growth
relative
to controls.
the results
of the
drogens
in genetic
lation
male
changin which
the summer
solstice
[1,4]. Prepubertal
lambs
also
atonin
to monitor
photoperiod
changes
[28], but
pear
to respond
differently
to the same
photoperiod
sitions.
is at
pu-
female
enters
of puberty
is
as 15 weeks
female
lambs
in adult males
reproductive
transitions
[1]. Sheep
monitor
day lengths
via the pattern
of pineal
melatonin,
to steroid
begin
days of
male
begins
seasonal
of nocturnal
for review].
IN SEASONAL
DIFFERENCES
in the male
of the
of Mdenter
et al. [31]
in
have
of GnRH
from the hypothalamus
in the sheep.
It seems
likely that
and
androgenized
hypothalamus
female
to prevent
the
is blocked
release
of
GnRFI. We base this reasoning
on the pattern
of UI secretion in male and androgenized
females
following
acute
increases
in estradiol
and on the observation
that pituitary
responsiveness
to GnRII
is not sexually
differentiated
in the
sheep
[32].
and females
Initially,
estradiol
suppresses
[18]. In the female,
the UI
this
inhibition
and
androgenized
after
some
female
16
h. UI
recovers
UI in both
males
surge
overcomes
secretion
somewhat
in the
male
later.
This
pattern
of response
to estradiol
in the male and androgenized female
resembles
that of the hypothalamic-disconnect
ewe, in which
endogenous
GriRI-1 is blocked
to isolate
the
effects
of estradiol
on the pituitary
[33]. On the basis
of
these
similarities,
we hypothesize
that prenatal
androgens
prevent
the release
of GnRH
in response
to estradiol,
but
do not block
the associated
increased
pituitary
responsiveness.
It is significant
that surge-like
UI secretion
following
tradiol
treatment
was observed
in 3 of 7 males
during
first surge
induction.
Rarely,
increases
in UI have been
esthe
re-
ported
but
these
serve
one
the
in
the
normal
male
in
response
were
not repeatable
[18]. Likewise,
any UI increase
during
the second
year later.
gonadotropin
These
results
suggest
surge
mechanism
to
estradiol,
we did not obsurge
induction
that masculinization
in the sheep
may
of
be
396
WOOD
intermediate
between
that
of the
rat,
completely
eliminated
[34], and
surge
is inducible
in the normal
At the present
time,
androgens
act to induce
and location
of GnRH
neuronal
However,
processes
it appears
secretion.
of tonic
probably
is
in which
Prenatal
on
differentiated
diverse
effects
masculinize
neurons
12.
Hauger
tradiol,
13.
and
controlling
FJP,
ML,
hormone
secretion
15.
GD,
and
LEJr,
luteinizing
differentiation
ovine
sexual
opioid
regulation
maturation
in the
of pulsatile
female sheep.
Midgley
AR, Nalbandov
AV. Radioimmunoassay
for
hormone.
Endocrinology
1969; 84:1166-1173.
of the brain of the sheep. INSERM 1974; 32:121-
142.
Clarke
Ii, Scaramuzzi
and behavioural
71:175-176.
control
during
101:807-817.
125:369-383.
Reichert
RV. Sexual
Short
Endocrinology
1977;
Foster DL Endogenous
secretion.
UI
Schwartz
1989;
Niswender
bovine
16.
RJ, Short
Rv. Sexual
of the brain:
differentiation
of androgenized
responses
ewes
to estrogen.
endocrine
J Endocrinol
1976;
Ii, Scaramuzzi
P,J. Sexual
behavior
and UI secretion
in spayed
androgenized ewes after a single injection
of testosterone
or estradiol.
J Reprod
Fertil
1978; 52:313-320.
18. Karsch
FJ, Foster
DL Sexual
differentiation
of the mechanism
controlling
the
preovulatory
discharge
of luteinizing
hormone
in sheep.
Endocrinology
1975;
17.
to phoLU surge,
GnRH
tonic
Ebling
Endocrinology
14.
[35].
upon
the
based
luteinizing
developand surge
the response
eliminates
the
FJ, Foster DL A new concept
for control
of the estrous
cycle
upon temporal
relationship
between
luteinizing
hormone,
esprogesterone
in peripheral
serum
and evidence that progesterone
RL, Karsch
of the ewe
inhibits
system
during
control
of tonic
androgens
FOSTER
the
is not known
where
in the brain
sexual
differentiation.
The number
neurons
and the number
of their
neuroendocrine
the postnatal
via actions
surge
it
UI, most
likely
by altering
Furthermore,
testosterone
toperiod.
the
the primate,
male [11].
are not sexually
that androgens
have
the reproductive
ment
to influence
UI
in which
AND
release.
Clarke
97:373-379.
Karsch FJ, Foster DL, Legan SJ, Ryan KD, Peter GK. Control of the preovulatory
events in the ewe: interrelationships
of estradiol,
progesterone,
and lutelnizing
hormone.
Endocrinology
1979; 105:421-426.
20. Foster DL Preovulatory
gonadotropin
surge system of prepubertal
female sheep
is exquisitely
sensitive
to the stimulatory
feedback
action of estradiol.
Endocrinology 1984; 115:1186-1189.
21. Ebling
FJP, Foster
DL Phocoperiod
requirements
for puberty
differ from those
for the onset of the adult breeding
season
in the female
sheep. J Reprod
Fertil
19.
ACKNOWLEDGMENTS
We are grateful
to Mr. Lee H. Breasbois
lambs
for
experimentation;
gram
Sheep
Research
Doop
and
Mr.
Core
Ms. Tovaghgol
Gary
Facility
(Freeland,
for
animal
technical
high
Reproductive
conscientious
for expert
E. Adel
for providing
Ml)
of the
R McCalla
care;
advice
and
quality
Sciences
Pro-
Douglas
Mr.
assistance;
D.
Dr.
Mor.
ton B. Brown
for assistance
with statistical
analyses;
Mr. Michael
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