30 Dec

Endometrial Responsiveness to Oxytocin: DISCUSSION(1)

These studies do not support the hypothesis that endometrial responsiveness to ОТ is regulated by the amount of OTr in swine. These results indicated that the control of responsiveness to ОТ may occur through changes in coupling of the OTr to phospholipase С (PLC)-associated G protein (i.e., Gq) during diestrus and early pregnancy. Moreover, control of endometrial PGF2a secretion during early pregnancy in pigs is exerted at multiple cellular sites subsequent to the OTr.

It generally has been considered that endometrial OTr population density controls uterine sensitivity to ОТ and that control of pulsatile PGF2a release lies at the level of the OTr. Development of endometrial responsiveness to ОТ occurs within 12-24 h of stimulation of OTr expression. However, only modest nonsignificant changes in ОТ density were detected during diestrus in experiment 1 of the present study, and the initial increase in OTr mRNA that occurred between Days 5 and 12 in experiment 2 was not as closely associated with the onset of endometrial sensitivity to ОТ occurring between Days 14 and 16 in experiment 1 as occurred in previous studies with sheep.
In contrast, A1F4 activation of Gq stimulated PI hydrolysis and PGF2a secretion similarly on all days and indicated that the PGF2a secretory pathway between Gq and PGH endoperoxide synthase was fully functional on all days. Hydrolysis of PI and secretion of PGF2„ were stimulated by ОТ in cyclic gilts only on Day 16. Moreover, the response to ОТ on Day 16 was equivalent to that for A1F4~. Collectively, these results indicated that endometrial responsiveness to ОТ during diestrus in pigs may be controlled by coupling of OTr to Gq, although the contribution of modest changes in both expression and affinity of OTr cannot be excluded at the present time.

Categories: Early Pregnancy
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