Secretion of progesterone and 20 alpha-dihydroprogesterone during pregnancy in goats.

The relationships between the secretion of progesterone and 20 alpha-dihydroprogesterone and the sites of their production in pregnant goats were investigated. The progesterone concentration in the peripheral plasma increased after the goats mated, and was high from day 10 to day 140 of pregnancy. The 20 alpha-dihydroprogesterone concentration increased gradually from day 0 to day 140 after mating. The progesterone concentration before parturition decreased rapidly on day 1 prepartum, but the 20 alpha-dihydroprogesterone concentration remained high until the day of parturition and then began to fall. The ratio of progesterone to 20 alpha-dihydroprogesterone decreased and fell to less than one on day 1 prepartum. The plasma concentrations of progesterone in ovarian vein and of 20 alpha-dihydroprogesterone in the ovarian vein, umbilical vein, and umbilical artery were higher than those in the jugular vein. The ratio of progesterone to 20 alpha-dihydroprogesterone in placental tissue was less than one. These results suggest that in pregnant goats the main production site is the ovary for progesterone and the ovary and feto-placental unit for 20 alpha-dihydroprogesterone, and 20 alpha-dihydroprogesterone may take help to regulate progesterone production within the ovary and the feto-placental unit.