Changes in uterine secretion of prostaglandin F2 alpha and luteal secretion of progesterone in response to oxytocin during the porcine estrous cycle
1991
Kieborz, K.R. | Silvia, W.J. | Edgerton, L.A.
The purpose of this experiment was to determine whether the ability of oxytocin to stimulate uterine secretion of prostaglandin F(2 alpha) (PGF(2 alpha)) and luteal secretion of progesterone changes during the porcine estrous cycle. Nineteen multiparous sows were observed for estrus. After one estrous cycle of normal length, sows were assigned randomly to receive an injection of oxytocin (30 IU, i.v.) in the EARLY (Days 4-6; n = 6), MID (Days 9-11; n = 7), or LATE (Day 15; n = 6) stage of the estrous cycle. Concentrations of 13, 14-dihydro-15-keto-PGF(2 alpha) (PGFM) and progesterone were determined in jugular venous serum samples collected at -60, -45, -30, -15, 0, 2, 5, 10, 15, 30. 45, 60, 90, and 120 min after injection of oxytocin. The magnitudes of the PGFM and progesterone responses and the area under the respective response curves (AUC) were calculated for each sow. Concentrations of PGFM did not change in response to oxytocin administered during the EARLY or MID portions of the estrous cycle. Concentrations increased rapidly in 4 of 6 sows that received oxytocin LATE in the estrous cycle. Both magnitude and AUC were greater LATE in the estrous cycle than at either EARLY or MID cycle (p < 0.05). Thus, uterine secretory responsiveness to oxytocin develops between Days 11 and 15 postestrus in the sow. For progesterone, a transient increase was observed immediately following injection of oxytocin at MID cycle (p < 0.05), but not at the other times examined. Therefore, oxytocin appears to be capable of stimulating secretion of progesterone from the functionally mature corpus luteum.
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