Progesterone, but not LHRH or prostaglandin E2, induces sequential inhibition of lordosis to various lordogenic agents.
In experiment I we studied the capacity of progesterone (P) and two nonsteroidal agents that activate lordosis, but do not bind to the progestin receptor (PR), i.e. luteinizing hormone-releasing hormone (LHRH) and prostaglandin E2 (PGE2) to induce sequential inhibition (SI) in ovariectomized estradiol-primed rats. The administration of 1 mg P, 5 micrograms LHRH or 100 micrograms PGE2 induced significant lordosis within 4 h. An injection of 1 mg P, 24 h after the administration of the above lordogenic agents, induced significant lordosis in rats pretreated with LHRH or PGE2, but not in those pretreated with P. Thus, only P induced SI (p < 0.025). In experiment II we investigated if progestin-induced SI results in a reduced capacity of the subjects to respond only to P or to other lordogenic agents. The synthetic progestin norgestrel (400 micrograms administered 24 h earlier) significantly reduced the responsiveness to P (p < 0.01), LHRH (p < 0.01), PGE2 (p < 0.025) and dibutyryl cyclic AMP (db cAMP p < 0.01). Results suggest that SI is triggered only by agents that bind to the PR (experiment I) and that it decreases the responsiveness of rats not only to P but also to other lordogenic agents (experiment II).
González-Mariscal
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Centro de Investigación en Reproducción Animal, CINVESTAV-Universidad Autónoma de Tlaxcala, Mexico.
Melo
A I
AI
Beyer
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C
D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D015232:Dinoprostone / Q000494:pharmacology*; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D009644:Norgestrel / Q000494:pharmacology; D011374:Progesterone / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D012726:Sexual Behavior, Animal / Q000187:drug effects*
D007987:Gonadotropin-Releasing Hormone; D009644:Norgestrel; D011374:Progesterone; D003994:Bucladesine; D015232:Dinoprostone