Regulation of prostaglandin biosynthesis with flunixin meglumine in the bovine species.

Flunixin meglumine (FM) was injected in 2 oophorectomized cows to follow changes in basal levels of the main circulating prostaglandin (PG)F2 alpha metabolite, 15-ketodihydro-PGF2 alpha. A rapid decrease in the levels was seen after FM and the effect was lasting for about 6 h. Thus, to obtain a full effect of the drug on prostaglandin synthesis it is recommended that FM should be injected 4 times daily. This concept was further studied in 3 cycling heifers which obtained FM 4 times daily from day 15 of the estrous cycle for 7 days (totally 28 injections). During the period of drug administration, prostaglandin metabolite levels were decreased and the expected pulsatile release seen during luteolysis was delayed. The pulsatile release started about one day after cessation of treatment and then luteolysis occurred. Progesterone levels were normal during the FM treatment and dropped concomitantly with the pulsatile release of PGF2 alpha. The levels of progesterone decreased to low levels before the heifers showed signs of estrus and ovulated. The administration of FM causes a situation resembling that seen during early pregnancy and FM can be a useful tool in understanding the mechanism behind maternal recognition of pregnancy.