Different mechanisms for the inhibition of progesterone secretion by ACTH and corticosterone in pregnant rats.
The present study investigated possible sites through which ACTH or corticosterone inhibit progesterone secretion in pregnant rats, and the role of placental factors in blocking the inhibitory effect. The number of conceptuses was adjusted to one (IC group) or more than ten (FC group) on day 7 of pregnancy by aspirating the desired number. Serum concentrations of progesterone, testosterone and oestradiol were significantly (P less than 0.01) lower on day 15 in the 1C group than in the FC group. Corpora lutea (CL) obtained on day 15 were incubated for 6 h with corticosterone or ACTH. Corticosterone (1 mumol/l) significantly (P less than 0.05) inhibited progesterone secretion in the 1C group but not in the FC group. The inhibitory effect of corticosterone in the 1C group was completely blocked by co-addition of 1 mumol testosterone/l or 1 mumol oestradiol/l but not by 1 mumol dihydrotestosterone/l. ACTH (1 microgram/l-1 mg/l) had no direct effect on progesterone secretion in either the 1C or the FC groups, although ACTH apparently decreases progesterone secretion in vivo. Placentae obtained from rats of the FC group on day 15 were incubated for 24 h with or without ACTH (1 mg/l). The supernatant after placental incubation without ACTH significantly (P less than 0.01) increased progesterone secretion by the CL in both the 1C and FC groups, and also eliminated the inhibitory effect of corticosterone in the 1C group. The supernatant after placental incubation with ACTH also increased progesterone secretion in the FC group as effectively as the supernatant from the control incubation, but it had no effect in the 1C group.(ABSTRACT TRUNCATED AT 250 WORDS)
Sugino
N
N
Department of Obstetrics and Gynecology, Yamaguchi University School of Medicine, Ube, Japan.
Tamura
H
H
Nakamura
Y
Y
Ueda
K
K
Kato
H
H
D000324:Adrenocorticotropic Hormone / Q000494:pharmacology / Q000502:physiology*; D000818:Animals; D003338:Corpus Luteum / Q000187:drug effects / Q000378:metabolism*; D003345:Corticosterone / Q000494:pharmacology / Q000502:physiology*; D004958:Estradiol / Q000494:pharmacology; D005260:Female; D010920:Placenta / Q000502:physiology; D011247:Pregnancy; D011374:Progesterone / Q000378:metabolism*; D051381:Rats; D013739:Testosterone / Q000494:pharmacology
D013739:Testosterone; D011374:Progesterone; D004958:Estradiol; D000324:Adrenocorticotropic Hormone; D003345:Corticosterone