Prostaglandin E2 levels in uterine tissues and its relationship with uterine and luteal progesterone during the estrous cycle in dairy cows.

Endometrial tissue homogenates obtained at luteal and follicular stages of the estrous cycle were determined for prostaglandin E2 and progesterone contents by EIA and RIA, respectively. In Experiment 1, the concentrations and changes of PGE2 in uterine tissues collected by biopsy before slaughter and subsequent samples collected at 30, 60 and 90 min after slaughter were measured. No significant differences were observed in the concentration of PGE2 preslaughter or at 30 and 60 min post slaughter. However, there was a significant decrease (P<0.01) in PGE2 concentration 90 min post slaughter. In Experiment 2, the concentrations of PGE2 in the ipsilateral and contralateral horns in relation to corpus luteum function were compared. A significant (P<0.05) interaction was found between stages of estrous cycle (luteal vs follicular) based on CL progesterone content, and type of uterine horn (ipsilateral vs contralateral) on uterine PGE2 levels. The PGE2 concentration was significantly higher (P<0.01) at luteal phase than at follicular phase. During the luteal phase PGE2 concentrations in tissues of the uterine horn ipsilateral to the corpus luteum was significantly higher (P<0.01) than the contralateral horn. The PGE2 concentration was low and did not differ significantly between horns during follicular phase. A parallel increase (luteal: high) and decrease (follicular: low) in PGE2 and progesterone concentrations were observed. Correlations were observed for CL progesterone and uterine PGE2 concentrations as well as for PGE2 and progesterone concentrations in uterine tissues (r=0.70 and r=0.60, respectively). The results show that the increase in PGE2 concentrations in uterine tissues coincides with the high uterine progesterone concentrations during luteal phase.