RELATIONSHIP BETWEEN MATERNAL PLASMA PROGESTERONE CONCENTRATION AND INTERFERON-TAU SYNTHESIS BY THE CONCEPTUS IN CATTLE

The objective of this study was to determine the relationship between maternal progesterone concentration and conceptus synthesis of interfe ron-tau as an index of conceptus viability at the time of maternal rec ognition of pregnancy. Heifers of mixed beef breeds were randomly assi gned to receive 1 of 2 treatments: 1) intramuscular injection of 1500 IU hCG on Day 5 after artificial insemination (AI; n=12) or 2) intramu scular injection of saline on Day 5 after AI (n=17). Ovaries were scan ned daily by transrectal real-time ultrasonography. Progesterone conce ntrations were determined from daily blood samples collected from the jugular vein. Heifers were slaughtered on Day 18 after AI and conceptu s tissues were collected. These were incubated individually at 37 degr ees C in RPMI medium, and supernatant collected after 24 h. Conceptus secretory products in the supernatant were analyzed for interferon con centration by antiviral assay using vesicular stomatitis virus. Transr ectal ultrasonography showed all heifers that received hCG had at leas t 1 extra corpus luteum(CL) in addition to the spontaneous CL formed f rom the previous ovulation (10 with 2 CL, 2 with 3 CL). A significant increase in plasma progesterone concentration was detected in pregnant heiferrs treated with hCG (n=9) vs pregnant control heifers(n=11; P < 0.001). There was a tendency for an increase (P=0.059) in synthesis o f interferon-tau by conceptuses from hCG-treated heifers compared to c ontrol heifers. Maternal plasma progesterone concentrations were corre lated with interferon-tau production by the conceptuses (r = 0.593 P < 0.006), suggesting that higher maternal progesterone may provide a mo re suitable environment for the developing conceptus. (C) 1997 by Else vier Science Inc.