Local transfer of prostaglandin F 2α from the uterine lumen into the venous and arterial blood and into the uterine, mesometrial and ovarian tissue on Day 18 of pregnancy in the pig

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Gilts of similar age and body mass were mated with a normal (eight gilts) or vasectomized boar (three gilts). On Day 17 of pregnancy or the oestrous cycle, silastic catheters were implanted into the carotid artery, utero-ovarian vein, uterine artery branch (5–10 cm from the uterine horn) and into the lumen of each uterine horn through the oviduct. The lumens of both uterine horns were ligated close to the cervix. Next day 3H-PGF 2α (10 8 dpm) dissolved in 30 ml of saline was injected into the lumen of the experimental horn and 30 ml of saline into the control horn of conscious animals. Plasma samples were collected through two catheters from the experimental horn and from the carotid artery, and the radioactivity was measured every 10 min for 2 h. In pregnant gilts the radioactivity in the plasma samples collected simultaneously from the uterine artery branch on the experimental side was 50–69% higher than in the carotid artery ( P<0.05) while no significant difference was observed in nonpregnant gilts. The animals were sacrificed at 120 min of the experiment and the radioactivity in different segments of the uterine tissue (endometrium and myometrium) and in different samples of mesometrium and mesovarium was measured. In the experimental horn of pregnant as well as of nonpregnant gilts the radioactivity of the endometrium was much higher than in the myometrium ( P<0.001). The results were opposite in the control horn ( P<0.001). In pregnant, contrary to nonpregnant, gilts, significant differences in the radioactivity of mesometrial tissues taken from the same area 5–10 cm from the uterine horn were found, i.e.: 24.2±9.5, 14.6±3.1 and 7.2± 1.3 (× 10 3dpm/g) in the wall of the vein, wall of the artery and the muscular layer of the mesometrium, respectively ( P<0.01). Labelled prostaglandin was found in the uterine flushing of the control horn (142.3±17.2 × 10 3dpm and 112.9±40.1 × 10 3dpm for pregnant and nonpregnant gilts respectively). This concentration exceeded many fold the concentration in the blood supplying the uterine horn. It is suggested that the back transfer of PGF 2α from the venous blood into the uterus with the arterial blood, and the ability of the uterine vein and artery wall to bind and retain PGF 2α may be a part of the complex corpus luteum protecting mechanism during early pregnancy.