EFFECT OF INTRAUTERINE INFUSION OF RECOMBINANT ALPHA(I)1 ON LUTEAL-PHASE DURATION AND OXYTOCIN-INDUCED RELEASE OF 13,14-DIHYDRO-15-KETO-PROSTAGLANDIN F2-ALPHA IN POSTPARTUM BEEF-COWS

The objective of this study was to determine if oxytocin-induced relea se of prostaglandin F-2 alpha: (PGF(2 alpha); measured by the stable m etabolite, 13,14-dihydro-15-keto-prostaglandin F-2 alpha (PGFM)) was i nhibited following intrauterine infusion of bovine interferon-alpha(1) 1 (rboIFN alpha(1)1) into postpartum cows anticipated to have short es trous cycles following first ovulation postpartum. Cows expected to ha ve short estrous cycles were assigned to receive twice daily intrauter ine infusions of either placebo (SCP; n = 11) or 2 mg rboIFN alpha(1)1 (SCIFN; n = 14) on Days 1-16 following hCG injection (2500 IU; day 0) on Days 30 or 31 postpartum. On Day 5 following hCG, each cow was inj ected with 100 IU oxytocin (i.v.) to induce the release of uterine PGF (2 alpha) (as measured by PGFM). Other treatment groups consisted of c ows expected to have normal estrous cycle lengths following pretreatme nt with a 9 day norgestomet implant on Days 21 or 22 postpartum follow ed by hCG injection to induce ovulation. Cows expected to have normal estrous cycle lengths received twice daily intrauterine infusions of e ither placebo from Days 1 to 16 of the cycle and 100 IU oxytocin (i.v. ) on Day 5 (NCPE; n = 11) or twice daily infusions of placebo (NCPL; n = 7) or rboIFN alpha(1)1 (NCIFN; n = 10), from Day 13 post-hCG inject ion until luteolysis. Oxytocin was injected (100 IU; i.v.) into cows i n the NCPL and NCIFN groups on Day 16. The calculated areas under the curve (arbitrary PGFM units) were: 164 +/- 18 units, 96 +/- 16 units, 93 +/- 18 units, 137 +/- 27 units and 53 +/- 20 units for SCP, SCIFN, NCPE, NCPL and NCIFN, respectively (SCIFN < SCP; NCIFN < NCPL; P < 0.0 15). Mean luteal phase length was calculated as the number of days fro m injection of hCG until progesterone declined to below 0.5 ng ml(-1) and was: 6.7 +/- 1.0 days, 10.5 +/- 0.9 days, 12.0 +/- 1.0 days, 18.0 +/- 1.3 days and 20.7 +/- 1.1 days for SCP, SCIFN, NCPE, NCPL and NCIF N, respectively (SCP < SCIFN = NCPE < NCPL = NCIFN; P < 0.01). In summ ary, luteal phase lengths were increased and oxytocin-induced release of PGFM was reduced by rboIFN alpha(1)1 infusion in cows anticipated t o have short luteal phases.