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Biology of Reproduction, Vol 21, 1015-1023, Copyright © 1979 by Society for the Study of Reproduction
1 Department of Physiology,
School of Medicine,
University of Maryland,
Baltimore, Maryland 21201 These studies determined whether fluctuating physiological plasma progesterone (P) concentrations facilitate as well as inhibit spontaneous LH and FSH surges in E2 primed, ovariectomized
(OVX) rats. Two weeks after ovariectomy (Day 0), Silastic implants of estradiol-17 In a separate experiment, the pituitary LH responses to 2 i.v. pulse injections of LHRH spaced
120 min apart were evaluated in 2 week OVX animals given E2, E2 P or no steroid pretreatment.
Both steroid treated groups released more LH than did nonsteroid treated animals in response to
either LHRH injection. As well, pituitary LH responses to LHRH in E2 and E2 P treated rats were
greater after the second than after the first injection. However, P treatment of E2 primed animals
tended to enhance the self-priming action of LHRH. These data demonstrate that: 1) low physiological P levels can facilitate spontaneous LH and FSH surges on Day 3 as well as inhibit these
discharges on Day 4 in E2 primed animals; 2) these P-induced responses are dose dependent; and 3)
the facilitory action of P is exerted on CNS neurons and possibly on pituitary gonadotrophs.
(E2) were
inserted s.c. at 0900 h into all animals. Silastic P implants of various lengths, which produced
plasma P levels ranging between 5-20 ng/ml, were implanted s.c. into separate groups of E2 treated
OVX rats 72 h later (Day 3). Another group of E2 treated rats received a s.c. injection of 2 mg P
on Day 3. As plasma P levels increased, greater peak plasma LU and FSH levels were achieved during the afternoon of Day 3. However, higher concentrations of plasma P were required to affect
significantly spontaneous FSH than LH surges. Further, as plasma levels of P increased, the onset
of release of both gonadotropins occurred earlier in the afternoon of Day 3. When plasma P levels
were increased above 17 ng/ml, further facilitation of either gonadotropin surge was not observed.
Regardless of the plasma P levels present on Day 3, this steroid did not inhibit spontaneous LH
surges on this day. In contrast, the absence of spontaneous gonadotropin surges on Day 4 was
related to P concentrations present in plasma on Days 3 and 4.
Note:
ACKNOWLEDGMENTS
The authors wish to thank Drs. Gordon Niswender,
L. E. Reichert, Jr. and the NIAMDD for antisera to
ovine LH (G.D.N. no. 15) and progesterone (G.D.N.
no. 337), for the purified ovine LH for iodination and
for the FSH RIA kit, respectively. We also wish to
acknowledge the technical assistance of Ms. Viktoria
Reck-Malleczewen.
This article has been cited by other articles:
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  P. Micevych and K. Sinchak Synthesis and Function of Hypothalamic Neuroprogesterone in Reproduction Endocrinology, June 1, 2008; 149(6): 2739 - 2742. [Abstract] [Full Text] [PDF]
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 C. D. Buchanan, V. B. Mahesh, and D. W. Brann Estrogen-Astrocyte-Luteinizing Hormone-Releasing Hormone Signaling: A Rolefor Transforming Growth Factor-{beta}1 Biol Reprod, June 1, 2000; 62(6): 1710 - 1721. [Abstract] [Full Text]
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 K. M. Ogilvie and C. Rivier Effect of Alcohol on the Proestrous Surge of Luteinizing Hormone (LH) and the Activation of LH-Releasing Hormone (LHRH) Neurons in the Female Rat J. Neurosci., April 1, 1997; 17(7): 2595 - 2604. [Abstract] [Full Text] [PDF]
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 V. Ramirez, D Dluzen, and D Lin Progesterone administration in vivo stimulates release of luteinizing hormone-releasing hormone in vitro Science, May 30, 1980; 208(4447): 1037 - 1039. [Abstract] [PDF]
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