Endocrinology, Vol 137, 1226-1232, Copyright © 1996 by Endocrine Society

ARTICLES

RU486 on an estrogen background blocks the rise in serum follicle- stimulating hormone induced by antiserum to inhibin or ovariectomy

KL Knox, SJ Ringstrom, M Szabo, CA Perlyn, S Sutandi and NB Schwartz
Department of Neurobiology and Physiology, Northwestern University, Evanston, Illinois 60208, USA.

We used passive immunization with an antiserum to the alpha-subunit of inhibin (anti-I) or acute ovariectomy to investigate the relationship between serum inhibin levels and FSH secretion in the presence of the progesterone/glucocorticoid antagonist RU486. We demonstrated previously that 1) anti-I administered at 1700 h causes serum FSH to rise on the morning of estrus, even in the presence of a GnRH antagonist, when the two treatments are delivered on proestrus; and that 2) RU486 given on proestrus (1230 h), a time when serum estradiol levels are high, not only blocks the natural secondary FSH surge, but also suppresses the anti-I-induced rise in serum FSH on the morning of estrus. We have now extended our studies of the relationship between inhibin and RU486 to investigate treatment with RU486 and anti-I on a different day of the cycle, estrus, when serum estradiol levels are low. When both RU486 and anti-I were given on estrus (1230 and 1700 h, respectively), RU486 failed to block the anti-I-induced rise in serum FSH on the next morning of metestrus, in contrast to the blockade seen with RU486 treatment on the day of proestrus. However, pretreatment with estradiol benzoate (50 microgram) on the evening of proestrus, before the RU486 and anti-I treatment on estrus, caused RU486 to suppress the effects of anti-I on serum FSH, as it does when given on proestrus. We then repeated the study, using ovariectomy on proestrus or estrus (1700 h) to raise serum FSH, and assessed the effects of RU486 treatment at proestrus and estrus and estradiol benzoate treatment on proestrus. Our results indicate that treatment with RU486 can block the postovariectomy rise in serum FSH only in the presence of high circulating estradiol levels. We conclude that the inhibitory action of RU486 on FSH secretion after a fall in serum inhibin depends on a precedent estradiol background, probably due to induction of progesterone receptors by estradiol.

This article has been cited by other articles:

				J. S. Schneider, C. Burgess, N. C. Sleiter, L. L. DonCarlos, J. P. Lydon, B. O'Malley, and J. E. Levine Enhanced Sexual Behaviors and Androgen Receptor Immunoreactivity in the Male Progesterone Receptor Knockout Mouse Endocrinology, October 1, 2005; 146(10): 4340 - 4348. [Abstract] [Full Text] [PDF]

				M. Szabo, S. M. Kilen, S. J. Nho, and N. B. Schwartz Progesterone Receptor A and B Messenger Ribonucleic Acid Levels in the Anterior Pituitary of Rats Are Regulated by Estrogen Biol Reprod, January 1, 2000; 62(1): 95 - 102. [Abstract] [Full Text]

				F. Gaytán, C. Bellido, C. Morales, and J.E. Sánchez-Criado Both Prolactin and Progesterone in Proestrus Are Necessary for the Induction of Apoptosis in the Regressing Corpus Luteum of the Rat Biol Reprod, November 1, 1998; 59(5): 1200 - 1206. [Abstract] [Full Text]

				M. Szabo, S. M. Kilen, S. Saberi, S. J. Ringstrom, and N. B. Schwartz Antiprogestins Suppress Basal and Activin-Stimulated Follicle-Stimulating Hormone Secretion in an Estrogen-Dependent Manner Endocrinology, May 1, 1998; 139(5): 2223 - 2228. [Abstract] [Full Text] [PDF]

				S. J. Ringstrom, M. Szabo, S. M. Kilen, S. Saberi, K. L. Knox, and N. B. Schwartz The Antiprogestins RU486 and ZK98299 Affect Follicle-Stimulating Hormone Secretion Differentially on Estrus, but not on Proestrus Endocrinology, June 1, 1997; 138(6): 2286 - 2290. [Abstract] [Full Text] [PDF]