Effect of dexcloprostenol on endogenous prostaglandin F2α release in dairy heifers

Cloprostenol was previously believed to be unable to release endogenous prostaglandin F2α (PGF2α) when administered during early bovine diestrus. A prostaglandin release is, however, seen in late diestrus. The aim of this study is to find out whether dexcloprostoenol (containing the only biologically active isomer, d-isomer, of cloprostenol) induces endogenous PGF2α release during early and late diestrus. Twelve heifers of the Finnish Ayrshire breed were allocated into two equal groups. Their estrous cycles were synchronized with dexcloprostenol. A further luteolysis was induced with 0.15 mg of dexcloprostenol either on Day 7 (group D7 or early diestrus) or on Day 14 (group D14 or late diestrus) after ovulation. Blood for progesterone and the PGF2α metabolite 15-ketodihydro-PGF2α determinations was collected immediately before dexcloprostenol treatment and thereafter every second hour for 48 h. Five of the six heifers in both groups showed significantly increased blood levels of 15-ketodihydro-PGF2α at some time during the 48-h experimental period. The intervals from treatment to the first significant increases of the PGF2α metabolite were 32.8 ± 2.3 h (min. 30 h, max. 36 h) and 20.0 ± 4.2 h (min. 14 h, max. 24 h) in groups D7 and D14, respectively (P < 0.01). We have concluded that dexcloprostenol induced endogenous PGF2α release in most cases, regardless the time of its administration (early or late diestrus). This release, however, differs from that observed during spontaneous luteolysis.