| Summary: | The potential role of arachidonic acid as an intracellular regulator of aromatase activity of human term trophoblast was investigated in short term (3 h) incubations. Melittin, a known activator of phospholipase A₂,suppressed the aromatase activity of physically dissociated trophoblast cells in a dose-dependent manner. Indomethacin (10⁻⁴M), a cyclooxygenase inhibitor of arachidonic acid metabolism, suppressed aromatase activity and potentiated the inhibitory effect of melittin (P<0.05). Nordihydroguaiaretic acid (NDGA) alone, a lipoxygenase inhibitor, also decreased aromatase activity but did not affect the inhibitory effect of melittin. The addition of exogenous arachidonic acid (10⁻⁴M) to trophoblast cells decreased aromatase activity in a dose-dependent manner (P<0.01). Arachidonic acid metabolites such as prostaglandin F₂a, (10⁻⁶M) and leukotriene B4 (10⁻⁶M) had no effect on aromatase activity. The presence of hypoxanthine (10⁻³M) and xanthine oxidase (10 mU/ml), also attenuated aromatase activity in trophoblast cells (P<0.01), presumably via an elevation of intracellular free arachidonic acid concentration. Interestingly, melittin suppressed aromatase activity during short term (3 h) incubation but was ineffective on trophoblast cells from 24 h and 48 h incubations. The role of cAMP in the action of aromatase activity was investigated. Cyclic AMP had no effect on 17ϐ-estradiol production in human trophoblast cells during short term (3 h) incubation. But cAMP enhanced 17ϐ-estradiol production during 24h and 48 h incubations. These results suggested that aromatase activity of freshly obtained term trophoblast cells was at or near maximal capacity or cAMP may not have been able to exert its steroidogenic action on human term trophoblast cells rapidly enough to be detected during a 3 h incubation. Cyclic AMP stimulated aromatase activity on human term trophoblast cells during 24 h and 48 h incubation, suggesting that cAMP achieves its actions by increasing protein and mRNA synthesis.
Effects of arachidonic acid, cAMP, hCG and 25-OH-cholesterol on progesterone production were investigated. None of them had effects on progesterone production during a 3 h incubation. These observations suggest that fresh term trophoblast cells may perform at or near optimal capacity on progesterone production.
The results supported the potential intracellular regulatory role of arachidonic acid on aromatase activity in human term placenta.
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