Biol Reprod Keystone Symposia Conference on Frontiers in Reproductive Biology & Regulation of Fertility.
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Biology of Reproduction, Vol 13, 218-222, Copyright © 1975 by Society for the Study of Reproduction

Estrogen and Progesterone Effects on the Neural Control of the Preovulatory LH Release in the Golden Hamster

REID L. NORMAN 1

1 Reproductive Physiology Oregon Regional Primate Research Center Beaverton, Oregon 97005


Serum LH was measured in blood samples taken at 1200, 1600, and 2000 from intact and ovx (ovariectomized at 1100) proestrous hamsters after treatment with phenobarbital (Phen), estradiol benzoate (EB) or progesterone (P), or various combinations of these drugs. By 1600, the serum LH concentration was greater in intact hamsters than in ovx animals (2800 vs 400 ng/ml), and in both groups LH release was blocked by Phen. Sham-ovariectomy had no effect on 1600 serum LH levels. In intact females, P prolonged LH release but did not affect LH concentration at 1600 (3000 ng/ml) whereas in ovx animals P more than doubled the LH concentration at 1600 (1000 ng/ml). Phen plus P delayed and depressed the LH surge in intact animals but did not affect the LH pattern achieved by P alone in ovx animals. Therefore, the ability of P to overcome the Phen block of LH release was inhibited by the ovary. Additional groups of ovx animals were given EB in combination with P and Phen to determine whether estrogen was the substance which interfered with this action of P.

Ovx hamsters given EB had twice the amount of serum LH at 1600 as those given P alone (1900 vs 1000 ng/ml). Estrogen (EB) plus P caused an LH release similar to that with EB alone at 1600 (1800 ng/ml) and appeared to prolong the elevation measured at 2000. In ovx animals given EB, P, and Phen, LH release was delayed and depressed just as it was in intact animals which had received P and Phen.

Estrogen facilitation of LH release in the ovx hamsters is primarily at the neural level because EB given to animals ovx at 1100 proestrus did not affect the LH response to 5 ng LH-RH compared to animals that had not received EB.

These data indicate that although both estrogen and progesterone affect the quantity of LH released at the time of the proestrous LH surge, estrogen is the more effective. Moreover, in the presence of estrogen, the ability of progesterone to override the phenobarbital block of LH release is diminished.

 Submitted on January 8, 1975
Accepted on May 20, 1975






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Copyright © 1975 by the Society for the Study of Reproduction.