estrous cycle of either 4-or 5-day length, two transient increases in ovarian progesterone secretion are ob- served, one. (preovulatory increase) in the afternoon.
BIOLOGY
OF
REPRODUCTION
36,
(1987)
599-605
Preovu latory Secretion of Progesterone, Luteinizing Hormone, and Prolactin in 4-Day and 5-Day Cycling Rats
INORU
HASHIMOTO,’ MITSUMORI
NAHOKO
ISOMOTO,
KAWAMINAMI, and
CHIAKI
NOBUYUKI
Laboratory
of
of
Veterinary
ETO,
SUNAZUKA,
UEKI
Veterinary
Kitasato School
MUTSUKO
Physiology
University Medicine
and
Animal
Aomori
034,
Japan
Towada-shi,
Sciences
ABSTRACT Timing of ovulation and changes in plasma progesterone, luteinizing during periovulatory stages were determined in Holtzman rats exhibiting artificial illumination from 0500 to 1900 h. The 5-day cycling rats estrus, whereas on estrus. Onset
some time
and
cycling
the
5-day
proestrus,
while
plasma gesterone the
LH
5-day
the
of the 4-day of preovulatory rats. first
cycling animals ovulated LH and progesterone
Peak rises
levels and
of plasma
peak
values
LH
cycling
rats
than
in the
4-day
cycling
and
A tentative
working
hypothesis
concerning
increases
in
ovarian
metestrus
1900 0330 In
that during length, two
progesterone
the
etiology
(Eto et al., 1962;
the rat transient
secretion
are
a few
at
hours
1700
to
earlier
1900
than
h 4-
h on
those
of
h on proestrus as well as plasma proh on estrus were significantly lower in
contrast,
PRL
levels
from
1500
through
of the
5-day
cycle
has
been
secretion
proposed.
from
a new
crop
of corpora
lutea formed during the cycle (Hashimoto and Wiest, 1969a,b; Furudate et al., 1975). The 5-day cycling
ob-
rats
afternoon increase)
Hashimoto
h and others as late as 1130 h on proestrus in both the
measured
evident
in progesterone
served, one (preovulatory increase) in the of proestrus and the other (postovulatory during
