04 Jan

Endometrial Responsiveness to Oxytocin: DISCUSSION(6)


The current studies showed that PGF2a secretion was not reduced during pregnancy in pigs as it was in cattle. This is in agreement with the proposal that a conceptus estradiol-mediated shift in orientation of endometrial PGF2a secretion from an endocrine direction to an exocrine one, rather than a decrease in total PGF2a production, prevented the uterine luteolysin from reaching the ovary and causing corpus luteum regression. Although the direction of secretion was not assessed in the current study, previous studies indicated that total PGF2a secretion remained high, but endocrine secretion of PGF2q decreased through Day 16 of pregnancy under the influence of con-ceptus-secreted estradiol.

In the present study, this presumed increase in exocrine PGF2(l secretion would be consistent with the previous suggestion that exocrine secretion of PGF2a in pigs is not mediated through activation of PLC by ОТ and a corresponding increase in PI hydrolysis because basal and AlF4“-stimulated PI hydrolysis on Days 14-16, as well as OT-stimulated PI hydrolysis on Day 16, were suppressed during pregnancy, but PGF2a secretion was not. Further, only endometrial stromal cells from cyclic gilts responded to ОТ treatment with increased PI hydrolysis and PGF2a secretion, whereas luminal epithelial cells (the cells closest to the uterine lumen) were unresponsive to ОТ, although they had the highest basal rate of PGF2ci secretion. This indicated that the cells closest to the uterine vasculature and most likely to be responsible for endocrine secretion of PGF2a (i.e., stromal cells) were responsive to ОТ, whereas those cells most likely to be responsible for exocrine PGF2(, release were unresponsive to ОТ.

Categories: Early Pregnancy
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