Timing of prostaglandin F2α release episodes and oxytocin receptor development during luteolysis in the cow

The timing of PGF2α release and the timing and extent of the rise in endometrial oxytocin receptors was determined in relation to the timing of the progesterone fall during luteolysis in cycling cows. In cows undergoing luteolysis (n = 6), measurement of PGF2α metabolite in hourly plasma samples collected during daily 10 h sampling periods identified a total of 2.2 ± 0.5 PGF2α release episodes per animal, each of 4.0 ± 0.4 h duration. In cows in which luteolysis was not observed (n = 4) no PGF2α release episodes were identified. In a further three cows in which additional repeated uterine biopsies were collected on days 15, 17, 19, 21 and 23, endometrial oxytocin receptors were initially undetectable (<15 fmol/mg protein) but had increased to 120 ± 19 fmol/mg protein prior to the initiation of PGF2α release episodes. Receptor concentrations then continued to increase reaching peak concentrations of 651 ± 142 after luteolysis had been completed.