Ovarian venous outflow, progesterone and 17 beta-oestradiol secretion and peripheral blood level during pregnancy in the rat.

Blood was collected from the right ovarian vein on every third day of pregnancy in rats and the ovarian venous outflow and haematocrit were measured. Progesterone and 17 beta-oestradiol were determined by RIA from the ovarian venous and peripheral blood and the secretion rate of progesterone (ng/min) and 17 beta-oestradiol (pg/min) was calculated. An elevated level of ovarian venous blood flow was found on day 9 and 12 of pregnancy when the progesterone secretion reached the highest values. Blood flow began to decrease on day 15, the progesterone secretion rate on day 18. On day 21, progesterone secretion rate returned to the day-1 level, however, at this time the progesterone concentration of ovarian venous blood and peripheral blood remained significantly elevated. Secretion rate of 17 beta-oestradiol showed a gradually tendency to increase from day 12 reaching the highest value on day 21. Ovarian and peripheral venous blood level of 17 beta-oestradiol increased parallelly from day 15. The high level of ovarian blood flow and progesterone secretion in mid-pregnancy is suggested to be the result of the stimulation of luteotropic material originating from the placenta. Since the ovarian venous blood flow changes during pregnancy, the hormone concentration of ovarian venous blood is not a reliable indicator of hormone production.