Lack of short-term modulation of in vitro placental progesterone secretion in sheep.
Experiments were performed in order to determine whether progesterone secretion in the ovine placenta can be short-term regulated. There was an increase in progesterone content per unit weight in ovine fetal cotyledons as gestation progressed: 17.0 +/- 4.7 ng/100 mg of wet tissue in ewes between 40 and 54 days of pregnancy (n = 7) and 70.7 +/- 18.8 (n = 9) between 100 and 118 days. At all stages of pregnancy, neither progesterone nor 20 alpha-dihydroprogesterone synthesis were significantly affected when fetal cotyledons were incubated for 3 h in the presence of LH, 8-Br-cAMP, GnRH agonist or GnRH antagonist. Addition of pregnenolone to the incubation medium increased progesterone secretion in a dose-dependent manner while addition of 25-hydroxycholesterol did not. These results suggest that the existent (basal) synthesis of progesterone reflects the maximal capacity of steroidogenesis through the cholesterol side-chain-cleavage system. In the presence of these precursors, LH, 8-Br-cAMP, the phorbol ester derivative PMA and calcium ionophore A23187 were not able to modify progesterone or 20 alpha-dihydroprogesterone synthesis. These results also suggest that LH or GnRH and the two signal mechanisms involved in their action, i.e. cAMP and Ca2+ sensitive-inositol phospholipid-dependent mechanisms are not implicated in the short-term regulation of progesterone synthesis in the ovine placenta.
de la Llosa-Hermier
M P
MP
Laboratoire des Hormones Polypeptidiques, C.N.R.S., Gif-sur-Yvette, France.
Zongazo
M A
MA
Martal
J
J
Hermier
C
C
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000818:Animals; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000031:analogs & derivatives / Q000037:antagonists & inhibitors / Q000494:pharmacology; D006888:Hydroxycholesterols / Q000378:metabolism; D007986:Luteinizing Hormone / Q000494:pharmacology; D010920:Placenta / Q000187:drug effects / Q000502:physiology*; D011247:Pregnancy; D011284:Pregnenolone / Q000378:metabolism; D011374:Progesterone / Q000378:metabolism*; D012756:Sheep
D006888:Hydroxycholesterols; D015124:8-Bromo Cyclic Adenosine Monophosphate; D007987:Gonadotropin-Releasing Hormone; D011374:Progesterone; C050812:LHRH, Ala(6)-; C037232:LHRH, Phe(2)-Pro(3)-Phe(6)-; D011284:Pregnenolone; C007997:25-hydroxycholesterol; D007986:Luteinizing Hormone