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Biology of Reproduction, Vol 23, 92-99, Copyright © 1980 by Society for the Study of Reproduction
1 Department of Physiology,
Ralph L. Smith Research Center,
University of Kansas Medical Center,
Kansas City, Kansas 66103 A model was developed for the study of atresia of preovulatory follicles in the hamster. The
effects of ovulatory delay on the ovarian follicular population, number of ova spontaneously
ovulated, and serum concentrations of steroids and gonadotropins were assessed. This model was
based on earlier observations of Everett and Sawyer (1950) who reported atresia of rat preovulatory follicles after 3 or 4 days of continued postponement of ovulation with sodium pentobarbital.
Cyclic hamsters weighing 90-110 g were maintained on a 14L:10D schedule (lights on at 0500 h).
Hamsters injected s.c. with 6.5 mg phenobarbital (Phen)/100 g BW at 1300 h on proestrus exhibited 1 day of ovulatory delay. Hamsters injected with 6.5 mg Phen at 1300 h on proestrus and also
with 13 mg Phen at 1200 h the next day, exhibited a 2-day delay; an additional injection of 19.5
mg Phen at 1200 h on the following day was required for 3 days of ovulatory delay. Histological
examination of the ovary revealed that the diameter of antral follicles on proestrus (561 ± 12 µm)
increased significantly after 1 day of ovulatory delay (680 ± 11 µm). After 2 days of ovulatory
delay, no significant alteration of antral follicular diameter was observed; however, on Day 3 of
ovulatory delay, the original set of preovulatory follicles exhibited early signs of atresia as evidenced by degenerating granulosa cells and by pyknotic nuclei within the oocytes. Interestingly, on
Day 3 of delay a new set of small-diameter antral follicles (527 ± 22 µm) was observed, indicating
that as the original set of preovulatory follicles became atretic they were gradually replaced by a
new set of antral follicles. Unlike the rat after 3 days of barbiturate administration, the hamster
ovulated 1.5 days later. This was due to the rapid recruitment of antral follicles as the original set
became atretic. The number of ova shed after 2 (17.9 ± 0.4 ova) and 3 (19.1 ± 0.6 ova) days of
delay (but not after 1-day delay, 12.5 ± 0.3 ova) was significantly higher than in untreated cyclic
hamsters (11.3 ± 0.7 ova). The higher ovulation rate may have been the result of recruitment of
stage V follicles observed only in delayed hamsters. Injections of Phen were required at 1200 h (1 h earlier than the first injection) to cause 2 and 3
days of ovulatory delay. Determination of the serum concentrations of LH and FSH during the
preovulatory period in delayed hamsters revealed that the rising phase of the LH surge occurred During the 3-day period of ovulatory delay, the serum estradiol concentrations were
1
h prior to that in the normal cyclic hamster. Successively larger doses of Phen, 13 and 19.5 mg,
were required to block ovulation for 2 and 3 days, respectively; this may be casually related to the
(classical) induction of tolerance to Phen.50 pg/ml
(correlating well with the normal number of antral follicles). The serum concentrations of progesterone (P) and androstenedione (A) at 1000 h were higher in delayed animals than in untreated
proestrous controls. On the morning of Day 1 of delay, the serum concentration of FSH was higher
than in proestrous controls. During delay, the serum LH level was not different from that in
proestrous controls. Collectively, these results indicate that the Phen-treated proestrous hamster is
a useful model for the study of atresia of preovulatory follicles. The delayed induced atresia
may be due to an alteration of the response of preovulatory follicle to gonadotropins since the
atresia occurred concomitantly with the recruitment of a new set of antral follicles. The increase in
the serum concentrations of P and A may be related to changes in steroidogenesis of the delayed
preovulatory follicles.
Note:
ACKNOWLEDGMENTS
I would like to thank Nancy Martin for her
expert technical assistance and Dr. Archie Vomachka
(Princeton University) for characterization of the
androstenedione antisera.
This article has been cited by other articles:
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  Y.-M. Zhang and S. K. Roy Downregulation of Follicle-Stimulating Hormone (FSH)-Receptor Messenger RNA Levels in the Hamster Ovary: Effect of the Endogenous and Exogenous FSH Biol Reprod, June 1, 2004; 70(6): 1580 - 1588. [Abstract] [Full Text] [PDF]
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