Production of 5 alpha-dihydroprogesterone during late pregnancy in the mare.
Changes in the progesterone metabolite 5 alpha-dihydroprogesterone (5 alpha-DHP) in maternal plasma in late gestation, and possible sites of production of this steroid were studied in pony and Thoroughbred mares by an enzyme-linked immunosorbant assay for 5 alpha-DHP. In Thoroughbred mares, plasma 5 alpha-DHP increased from 63.7 +/- 10.5 ng/ml (27 days pre-partum) to 161.7 +/- 30.8 ng/ml (1 day pre-partum) falling to 90.2 +/- 16.1 ng/ml on the day of parturition. In pony mares, values rose from 30.8 +/- 8.1 ng/ml (27 days pre-partum) to 79.1 +/- 30.8 ng/ml (3 days pre-partum) and then decreased to 28.2 +/- 7.1 ng/ml on the day of parturition. Concentrations of 5 alpha-DHP were greater in the umbilical and uterine veins than in the corresponding umbilical and uterine artery samples. Tissues incubated with isotopically-labelled substrates showed that the fetal placenta converted pregnenolone to progesterone (47.5 +/- 9.0%). Endometrium metabolised [3H]pregnenolone to progesterone and 5 alpha-DHP (11.0 +/- 3.0% and 7.8 +/- 2.4%, respectively), and [14C]progesterone to 5 alpha-DHP (9.3 +/- 2.5%). Deuterium-labelled substrates were used to confirm the identity of these products by gas chromatography-mass spectrometry. Negligible amounts of 5 alpha-DHP were formed by other fetal tissues (adrenal, liver, kidney and testis). The results show that 5 alpha-DHP production in late pregnancy is derived primarily from endometrial metabolism of pregnenolone and/or progesterone.
Hamon
M
M
AFRC Institute of Animal Physiology and Genetics Research, Babraham, Cambridge, U.K.
Clarke
S W
SW
Houghton
E
E
Fowden
A L
AL
Silver
M
M
Rossdale
P D
PD
Ousey
J C
JC
Heap
R B
RB
D043582:5-alpha-Dihydroprogesterone; D000818:Animals; D005260:Female; D005312:Fetal Blood / Q000737:chemistry; D005865:Gestational Age; D006736:Horses / Q000097:blood*; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000097:blood*; D011277:Pregnanediones / Q000097:blood* / Q000378:metabolism; D011284:Pregnenolone / Q000378:metabolism; D011374:Progesterone / Q000378:metabolism; D014599:Uterus / Q000098:blood supply
D011277:Pregnanediones; D011374:Progesterone; D011284:Pregnenolone; D043582:5-alpha-Dihydroprogesterone