Involvement of Arachidonic Acid and Its Products in the Mechanism of Progesterone Influence on Its Own Production in Vitro in Bovine Corpus Luteum

The involvement of the arachidonic acid (AA) products, noradrenaline (NA) and LH in the stimulatory effect of progesterone on its own synthesis was tested using slices of CL from days 5-10 of the oestrous cycle of cow. Slices of CL (45-50 mg) were pre-incubated for 24 h, then the medium was replaced with fresh medium and 45 min later was supplemented with LH (100 ng/ml) as a positive control, or used for an experimental treatment. In series of experiments (at least 3 CL per treatment) tissue was treated (each in four replicates) either with progesterone (10 M), progesterone antagonist (onapristone aP4, 10 M), arachidonic acid (20 μg/ml), INDOmethacin – cyclooxygenase inhibitor (10 M), nordihydroguairetic acid (NDGA; lipoxygenase inhibitor; 60 μg/ml) or NA (10 M). In the collected luteal slices after incubation, progesterone and 3β-HSD were determined. After 6 h of incubation with progesterone its concentration in CL slices was over 3-times higher compared to the control. This increased (P<0.01) 3β-HSD activity, while aP4 decreased (P<0.05) both 3β-HSD activity and progesterone concentrations in the tissue. Moreover, aP4, AA and INDO suppressed (P<0.05) stimulatory effect of progesterone on 3βhydroxysteroid dehydrogenase (3β-HSD) activity. NDGA did not affect progesterone influence on 3β-HSD activity. Neither INDO nor NDGA influenced the effect evoked by AA. Both LH or NA increased concentrations of progesterone and activity of 3β-HSD in the luteal tissue. But there were no additional increase of 3β-HSD activity when LH or NA was given together with progesterone. However, aP4 tended to diminish the stimulatory influence of NA and LH on the activity of 3β-HSD. We conclude that progesterone can support its own synthesis in the early stage of CL development acting via specific receptors. Both AA and cyclooxygenase products modifies this effect of progesterone whereas the lipoxygenase products do not. Progesterone receptors within CL seem to be crucial for the luteotrophic effect by LH and NA.