EFFECTS OF EXOGENOUS RECOMBINANT OVINE INTERFERON-TAU ON CIRCULATING CONCENTRATIONS OF PROGESTERONE, CORTISOL, LUTEINIZING-HORMONE, AND ANTIVIRAL ACTIVITY INTERESTROUS INTERVAL RECTAL TEMPERATURE AND UTERINE RESPONSE TO OXYTOCIN IN CYCLIC EWES

Interferon tau (IFN tau) is the conceptus-produced antiluteolytic sign al in ruminants. Three experiments examined the effects of s.c. admini stration of recombinant ovine (ro)IFN tau on interestrous interval (IE I), oxytocin (OT)-induced uterine prostaglandin F-2 alpha metabolite ( PGFM) production, rectal temperature (RT), respiration rate (RR), and plasma concentrations of progesterone, cortisol, LH, and antiviral act ivity (AVA) in plasma and uterine flushings. In experiment I, 20 ewes were treated s.c. with either 0, 1, 2, or 4 mg/day roIFN tau (0.7 x 10 (8) U/mg; 5 ewes/dosage) from Days 11 to 15 of the estrous cycle (estr us = Day 0) and were challenged with OT (30 IU) on Day 15. Jugular blo od samples were collected at -10, 0, 10, 20, 30, 40, 50, and 60 min re lative to the OT challenge and assayed for PGFM. Recombinant oIFN tau increased IEI (16.7, 18.7, and 22.6 +/- 0.6 days for 0, 2, and 4 mg ro IFN tau, respectively, p < 0.01). Recombinant oIFN tau did not affect peak PGFM response to OT (2309 +/- 172 pg/ml; p > 0.1). However, the 4 mg/day dosage delayed the time to peak PGFM (32.4 vs. 47.5 +/- 3.4 mi n; p < 0.01, 0 vs. 4 mg) and resulted in approximately 200% higher con centrations of PGFM at 60 min post-OT (0 vs. 4 mg/day, p < 0.07). Expe riment II was similar to experiment I, except that only the 0- and 4-m g/day dosages of roIFN tau were administered. Ewes were hysterectomize d on Day 16, and assay of uterine flushes detected no AVA from ewes tr eated with either 0 or 4 mg/day roIFN tau. In experiment III, 20 ewes were treated s.c. with either 0, 2, 4, or 6 mg roIFN tau on Day 12. Bl ood samples, RT, and RR were obtained at frequent intervals for 24 h, and plasma was assayed for progesterone, cortisol, LH, and AVA. Plasma AVA, which increased in a dose-dependent manner, was detectable withi n 60 min and remained elevated at 24 h compared to control values. RT (elevated 0.5-1.0 degrees C), RR, and cortisol increased in response t o all dosages of roIFN tau, with peak values occurring 150-180 min pos tinjection. For all dosages of roIFN tau, plasma progesterone declined from 120 to 360 min posttreatment and then returned to pretreatment v alues by 24 h (p < 0.01) as compared to controls. Overall, exogenous r oIFN tau altered uterine PGFM response to OT from a pulse to a gradual and sustained elevation and extended IEI with only a transient declin e in progesterone and mild hyperthermia, effects that are not expected to compromise pregnancy.