Effect of ovine conceptus and endometrial secretory products on luteal progesterone production in vitro

The objectives of this study were the following: (i) to determine if ovine conceptus secretory products are directly luteotrophic to luteal tissue in vitro and (ii) to determine if ovine conceptus secretory products stimulate endometrial tissue to secrete a luteotropin in vitro. Conceptus-conditioned medium (CCM) was prepared by incubating day 14 ovine conceptuses in minimal essential medium (MEM) for 24 h and harvesting the supernatant. Endometrium-conditioned CCM (E-CCM) and endometrium-conditioned medium (ECM) were prepared by incubating dispersed ovine endometrial cells from day 9–10 cycling ewes in CCM or MEM, respectively, for 16 h and harvesting the supernatants. Media, conditioned as described, were incubated at various dilutions with dispersed luteal cells from day 9–10 cycling ewes for 90 min or 6 h in the absence or presence of 50 ng/mL ovine luteinizing hormone (oLH). CCM did not alter progesterone (P4) production in the 90-min incubation but did increase (p < 0.05) P4 production in the 6-h incubation (1:4, 1:8, 1:16 dilutions). When coincubated with oLH, CCM did not increase P4 production above that stimulated by oLH alone. The effect of E-CCM was similar to CCM or ECM and did not differ significantly from basal. It is concluded that the day 14 ovine conceptus does secrete a factor that is able to directly stimulate P4 secretion by luteal cells in a 6-h, but not a 90-min, incubation. Conceptus secretory products did not stimulate endometrial cells to secrete a luteotropin. The data are consistent with the suggestion that the luteotrophic factor secreted by the conceptus is a prostaglandin of the E series.