LUTEAL MAINTENANCE DURING EARLY-PREGNANCY IN THE PIG - ROLE FOR PROSTAGLANDIN-E(2)(1,2)

We previously demonstrated that prostaglandin E2 (PGE) directly inhibi ts prostaglandin F2alpha (PGF)-induced regression of individual pig co rpora lutea (CL) in a dose dependent manner. The present experiments w ere conducted to 1) characterize and compare uterine secretion of PGE and PGF during the estrous cycle and early pregnancy and 2) evaluate t he local effect of the conceptus on uterine prostaglandin secretion an d associated CL function in unilaterally pregnant pigs. In Experiment 1, utero-ovarian venous blood samples were collected from two nonpregn ant and two pregnant gilts at 3-h intervals from day 10 through 16 (fi rst day of estrus or mating = day 0) for quantitation of uterine PGE a nd PGF secretion. In Experiment 2, gilts (n = 4) were made unilaterall y pregnant on day 2, and utero-ovarian venous catheters were placed bi laterally to determine if differences in PGE and/or PGF secretion migh t account for the known luteotrophic/antiluteolytic effect of the grav id uterine horn on the CL of the ipsilateral ovary. During the estrous cycle (Experiment 1), pulsatile secretion of PGF increased markedly o n day 13 and continued to increase through day 16. PGE secretion also increased from day 13 to 16 of the estrous cycle; however, concentrati ons of PGE remained at least 3-fold lower than those of PGF. In contra st to changes in non-mated gilts, prostaglandin secretion in mated gil ts peaked earlier (day 11-12), with PGE predominating. Thereafter, bot h PGE and PGF secretion declined to basal levels where they remained t hrough day 16 of pregnancy. During unilateral pregnancy (Experiment 2) , PGF concentration in nongravid and gravid horns was similar (P > 0.8 ). In contrast, PGE concentrations were greater (P < 0.06) in utero-ov arian venous blood draining the gravid uterine horn. This increase in PGE was associated with enhanced CL function on the ipsilateral ovary as evidenced by an elevated progesterone content and concentration as well as increased CL weights. These data are consistent with a role fo r conceptus-associated increases in uterine PGE secretion in the local stimulation of luteal function during early pregnancy in the pig.