The corpus luteum revisited: are the paradoxical effects of RU486 a clue to how progesterone stimulates its own secretion?
The progesterone (P) antagonist RU486 (RU) both lowers and raises P secretion by an apparently direct action on the corpus luteum. P receptors, however, exist in more than one form, and under certain conditions of P's target tissues, RU can act as a P agonist when bound to one of them. RU's paradoxical effects, therefore, may support the theory that P stimulates its own secretion since the conditions under which RU raises P secretion are always different from those in which it lowers it. These effects, however, occur in at least one species, the rat, in which luteal P receptors cannot be found, and there are several excellent reasons to think that the autocrine action of P in no way resembles its action in its target tissues. The system through which P controls its own secretion in all mammals, in other words, is still undiscovered.
Rothchild
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Case Western Reserve University, School of Medicine, Cleveland, OH 44106, USA.
D000818:Animals; D003338:Corpus Luteum / Q000187:drug effects* / Q000378:metabolism*; D005260:Female; D006727:Hormone Antagonists / Q000494:pharmacology*; D006801:Humans; D015735:Mifepristone / Q000494:pharmacology*; D011247:Pregnancy; D011374:Progesterone / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology*; D051381:Rats; D011980:Receptors, Progesterone / Q000502:physiology
D006727:Hormone Antagonists; D011980:Receptors, Progesterone; D015735:Mifepristone; D011374:Progesterone