Role of intraluteal prostaglandin F2α, progesterone and oxytocin in basal and pulsatile progesterone release from developing bovine corpus luteum

The present study examined the role of intra-luteal prostaglandin (PG) F2α, progesterone (P4) and oxytocin (OT) on the corpus luteum function by using specific hormone antagonists. Luteal cells from the developing CL (days 5–7 of the estrous cycle) were exposed to P4 antagonist (onapristone, OP, 10−4 M), OT antagonist (atosiban, AT; 10−6 M) or indomethacin (INDO; 10−4 M), for 12 h and then stimulated with PGF2α (10−8 M) for 4 h. Pre-treatment of the cells with OP, AT or INDO resulted in an increase in P4 secretion in response to PGF2α. To examine the temporal effects of P4, OT and PGs on P4 secretion, dispersed luteal cells were pre-exposed to OP, AT or INDO for 1, 2, 4, 6 or 12 h. Prostaglandin F2α stimulated P4 secretion (P < 0.05) after 2 h of pre-exposition. In the microdyalisis study, the spontaneous release of P4 from developing CL tissue was of pulsatile nature with irregular peaks at 1–2 h intervals. Treatment with OP increased the number of P4 peaks (P < 0.05), whereas AT and INDO significantly reduced the number of P4 peaks detected (P < 0.05). Interestingly, INDO completely blocked the pulsatile nature in the release of P4, but it secretion remained stable troughout the experimental period. These results demonstrate that luteal PGF2α, OT, and P4 are components of an autocrine/paracrine intra-ovarian regulatory system responsible for the episodic (pulsatile) release of P4 from the bovine CL during the early luteal phase.