Progesterone release of bovine corpus luteum in response to oxytocin in different culture systems

The aim of the present study was to investigate the effect of oxytocin (OT) on progesterone secretion by bovine corpus luteum (CL) in different culture systems. When luteal cells were cultured for 1, 2, 4 and 15 h at a density of 6 × 10⁴ cells/ml, OT (10⁷ M) did not affect progesterone secretion. On the other hand, bovine LH strongly stimulated progesterone secretion by the cells 215 h after incubation (P<0.01). In another experiment, a novel luteal slice culture system was used, in which luteal cells maintained cell-to-cell contact. Three slices (15-20 mg/a slice) from a CL were pre-incubated for 1 h, and then each slice was incubated for l h in a culture tube with a medium (3 ml) supplemented with and without bovine LH (100 ng/ml) or OT (10^-7 M). Slices were replaced every 1 h in a fresh medium during the 5 h incubation experiment. A 1-h stimulation with bovine LH and OT induced significant but different effects on the release of progesterone. OT acutely stimulated progesterone release at doses 10~7 M (155%; P<0.05), and bovine LH significantly increased progesterone release during and after stimulation (223%; P<0.01). These data support the hypothesis that OT plays a role in modulating the mechanisms of progesterone secretion as an intraluteal regulator. Differences observed between the two systems might be due to the presence or absence of cell-to-cell contact.