Estradiol-17β, Progesterone and 20α-Hydroxypregn-4-en-3-one in Rabbit Ovarian Venous Plasma. II. From Mating Through Implantation

The in vivo release of estradiol- 17β (E2), 20α-hydroxypregn-4-en-3-one (20α-OH) and progesterone (P) from the ovary between coitus and implantation was studied in 38 rabbits which had mated with fertile bucks. While P release remained constant, the release of E2 and 20α-OH, as measured in the ovarian venous effluent, increased following coitus to reach peak values between If and 4 hr. After this time the outputs of all 3 steroids began to decline. At ovulation E2 was no longer detectable and both progestins were at nadir ( <5 μg/ov/hr). During the 3-day period of tubal transport steroid output remained very low; but between days 4 and 6, when blastocysts lie free in the uterine lumen, E2 output rose, suggesting that implantation is preceded by a small rise in estrogen production. Between days 8 and 10, E2 release in rabbits with viable fetuses was 20.5 ± 4.1 pg/ov/hr and P release had increased to 23.8 ± 3.0 Mg/ov/hr. These data support the hypothesis that tubal transport of ova occurs during and, folio wing a period of acute ovarian steroid withdrawal. (Endocrinology89: 522,1971).