release, while ovarian venous pro- gesterone increases during the afternoon daily in pseudopregnant rats. (Yoshinaga and. Lin,. 1975). In hamsters. Seegal and.
BIOLOGY
OF
REPRODUCTION
13.617-622
Diurnal
(1975)
Rhythms
Lactating
in Gonadotropins
and Photoperiod S. BRIDGES2
ROBERT
and
University
of
Storrs,
Acyclic
BRUCE
in
Hamsters’
D. GOLDMAN
Biobehavioral
of
Department
and Progesterone
Induced
Sciences,
Connecticut,
Connecticut
06268
ABSTRACT
Levels
of
FSH, and progesterone in serum were measured in lactating hamsters and in hamsters acyclicity was induced with altered photoperiod. Lactating hamsters were found to have low titers of LH, FSH, and progesterone in serum at 0900 (lights on 0500-1900) on Days 4, 9, 14, and 19 of lactation and increased levels of these hormones at 1600. Levels of LU and FSH in serum at both 0900 and 1600 remained relatively constant throughout lactation. In contrast, levels of progesterone in serum obtained at both 0900 and 1600 sampling times increased as lactation progressed. Ovariectomy on Day 9 of lactation reduced serum levels of progesterone at both 0900 and 1600 and eliminated the afternoon surge in progesterone in animals bled 5 days after surgery. The levels and pattern of LH in serum remained unchanged after ovariectomy in lactating hamsters. However, serum FSH levels in the ovariectomized, lactating animals were elevated at both 0900 and 1600 when compared to levels present in intact, lactating hamsters bled LH, in which
at the same
times. which were acyclic due to altered photoperiod displayed similar patterns of LH, FSH, and progesterone in serum. Levels of LH, FSH, and progesterone in serum were low at 1000 (lights on 0500-1500) and were increased 2 to 10 fold at 1500. Ovariectomy was followed by lower progesterone levels in serum at 1000 and 1500 and eliminated the afternoon rise of this hormone. Serum levels of LH were unaffected by ovariectomy. As in lactating hamsters, levels of FSH in serum were elevated 3-4 days following ovariectomy at both bleeding times, but the levels were Females
higher at photoperiod
Animals diurnal
in
1975). recently
The terized
tissue a
while
al.,
ovarian
the
Seegal
daily
by
of
suggest
Lin,
marked
lack
condition
PIA
(1975)
be
are
hamsters of
follicles
found
in
found
in
also
search
Grant
2Present
Rutgers
was
supported
HD05481
awarded
Address:
Institute
University,
Newark,
part
by
PHS
Re-
NA
of
might
Furthermore,
exhibit secretion In these
a diurnal similar to the
present
possibilities
and
these
the
hamster
progesterone
the day The role
MATERIALS in
of
progesterone
by at
in both lactating of the ovaries in hormones
was
examined.
September 22, 1975. June 25, 1975.
#{176}Thisstudy
the
hamsters.
levels
the
histo-
ovaries
hamster. might
PIA
various times during and PIA hamsters.
1968),
of
serum
PtA
hamster gonadotropin
maintaining
Accepted Received
of
in the
we have investigated measuring serum LH, FSH,
hamsters
lactating
those
1970;
The
the
study
charac-
interstitial
(Reiter,
and
and
Blaha,
1974).
between
levels
high
the lactating pattern in
induced
proliferation
of antral also
that
also
and
Greenwald,
hamster
that
the
and
progesterone
(Lukaszewska
Leavitt
similarities
during
when high
is
tissue
progesterone
hamster are
to a short hamster. interstitial
of
1970;
lactating
daily
the
serum
Baranczuk
female.
ovaries
in
logical
gonado-
photoperiod
source
Greenwald,
pro-
and
Goldman in serum
and
surges
the
in
venous afternoon
Ovarian
1965).
in
levels
and
lactation or exposure hormones in the
probable
lactation
1972)
(Yoshinaga
rats
In hamsters reported
and
et
during
(GTH)
exhibit concentra-
(Freeman and Neill, 1972; rats display diurnal rhythms
1975)
(PIA)
states
hormone
(Butcher
increases
tropins acyclic
acyclic
serum
pseudopregnant
in
induced by of circulating
various
release,
gesterone
that acyclicity diurnal patterns
the
Pregnant
prolactin
indicate similar
(Greenwa!d,
of
pseudopregnant Smith et a!.,
by
INTRODUCTION
patterns
tions.
of
1500. These results is characterized
AND
METHODS
Animals
to B. D. Goldman. of Animal Behavior,
Thirty-six
obtained
NJ 07102.
617
female
from
our
hamsters
colony
(Mesocricetus (which
is
auratus) derived
from
BRIDGES
618
AND
GOLDMAN
Lakeview stock) were housed in a room in which lights were on 14 h each day (0500-1900). These females were mated to male hamsters. The pregnant females were checked daily for delivery, and the day of parturition was designated as Day 0 of lactation. All litters were culled to 5-7 pups on Day 3 of lactation. Twenty-four newly parturient hamsters were assigned to one of four groups (6 animals/group). Each group of hamsters was bled once at 0900 and again at 1600 on either Day 4, 9, 14, or 19 of lactation. The remaining 12 lactating hamsters were either ovariectomized (ovx) or sham-ovariectomized (sham-ovx) on Day 9 of lactation and then bled at 0900 and 1600 on Day 14 of lactation. Each animal was bled by heart puncture while under light ether anesthesia. Approximately 0.7-1.0 ml of blood was collected at each time, centrifuged at 4000 RPM for 20 mm, and sera were frozen at -20#{176}C until assayed for hormone content. A second group of 15 adult female hamsters obtained from Lakeview Hamster Colony (Newfield, NJ) were housed in a “short day” environment in which they were exposed to 10 h of light each day (lights on 0500-1500). Beginning 4 weeks after being placed in the “short day” environment these animals were checked daily for the discontinuation of the normal estrous cycle. After 6-8 weeks on short days each of the 15 females had become acyclic, as defined by the lack of an estrous smear for more than 8 consecutive days. Vaginal smears from all hamsters were checked daily for the remainder of the experiment to insure that each female was still acyclic. Two to four weeks after the cessation of cyclicity each animal was bled at each of three times: 1000, 1500, and 1900. These bleedings were made over a three day period such that each animal was bled once each day. Two weeks following the initial bleedings 13 of these acyclic hamsters (two animals died following the first bleedings) were assigned to one of two treatments. One group of 7 hamsters were ovariectomized, while the remaining 6 animals were sham-ovariectomized. Three to four days following surgery each animal was bled at 1000 and 1500. Blood was collected, centrifuged, and stored as described above.
interassay variability = 13.8 percent, intraassay variability = 8.9 percent. The accuracy of the progesterone assay was determined by adding a known quantity of progesterone (200, 500, or 1000 pg) to 50 ul of pooled male serum prior to extraction. The mean percent deviation from the expected mean for 12 samples (N=4 for each pg quantity of progesterone) was 2.8 percent. The value of measured progesterone for each sample did not differ by more than 21 percent from the expected value. The sensitivity of the progesterone assay was about 50 pg. Results were analyzed using ANOVA and the sign test (Siegel, 1956).
Hormone
lactation.
Assays
Sera were assayed for LH, FSH, and progesterone content. Serum levels of luteinizing hormone (LU) were determined by radioimmunoassay carried Out with antiserum raised against ovine LH (Niswender et al., 1968). Follicle-stimulating hormone (FSH) assays employed the NIAMDD Rat FSH Kit with Anti-Rat FSH S-6. Serum samples were assayed at volumes of 40 ul (LH) and 100 ul (LH and FSH). These assay systems have been validated for use in the hamster (Blake et al., 1973; Bast and Greenwald, 1974b). The sensitivity of these assays was approximately 5 ng for LH and 15 ng for FSH. Serum progesterone was assayed by radioimmunoassay following the methodology described by Abraham et al. (1971) with slight modifications in the extraction procedure (Johansson, 1970). The antibody to progesterone (#869-B) was obtained from Dr. G. D. Niswender (Niswender, 1973). Serum samples were assayed for progesterone content in duplicate at 50 ul volumes. The precision of the progesterone assay Was:
RESULTS
Lactating
Hamsters
LH. tion
The
are
were
values in
typically
1600.
An
0900.
an
there
er
of
levels
on
later
serum
not
as
Table and Day
1).
Serum on
of
serum
FSH
0900
4
levels
in
terone overall
day
of
lactation
were
still
(Table
significant
0900
(P
