Oxytocin-induced changes in plasma 13,14 dihydro-15-keto prostaglandin F2α concentrations on days 10, 20 and 30 postpartum in the bovine3

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Abstract
Eighteen suckled Brahman cows were allotted randomly to treatments arranged in a three-period crossover design according to calving date and prior treatment such that each cow received 30, 150 and 300 IU oxytocin (OT) i.v. on d 10, 20 or 30 postpartum. Blood was collected via an indwelling jugular catheter every 15 min for 195 min. Samples collected before OT administration were used to determine basal plasma 13, 14-dihydro-15-keto prostaglandin F2α (PGFM) concentration. Day, time and the day × dose interaction affected PGFM (P < .0001). All doses of OT elevated PGFM on all days postpartum (P < .0001). Basal PGFM was greater (P < .0001) on d 10 (252.2 ± 51.2 pg/ml) than on d 20 (78.2 ± 14.8 pg/ml) or on d 30 (64.8 ± 7.4 pg/ml). The rise in PGFM in response to OT was greatest on d 10 and decreased (P < .001) with increasing days postpartum. On d 10, 150 IU of OT caused a greater (P < .0007) rise in PGFM than either 30 or 300 IU. On d 20, the 300-IU dose raised PGFM more (P < .005) than either 30 or 150 IU, whereas on d 30 no differences among doses were detected. Cows had higher basal PGFM and a greater response to OT on d 10 postpartum than on d 20 or 30; cows were more responsive on d 20 than on d 30. All doses of OT elevated PGFM at all three times postpartum; however, differences between doses were not detected.(ABSTRACT TRUNCATED AT 250 WORDS)

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