Effect of epidermal growth factor on inhibin secretion in human placental cell culture

The effect of epidermal growth factor (EGF) on inhibin secretion was investigated in a primary culture of human placental cells. Dissociated cells were cultured with EGF, FSH, 8-Br-cAMP, and two agents known to increase intracellular cAMP. Inhibin level in the culture medium was measured by immunoenzymatic assay. Addition of EGF (0.1-1000 ng/ml) in the cell culture induced a dose-dependent increase of inhibin levels in the medium after 2 days of culture. Greater response of placental cells to EGF in the inhibin secretion occurred at the doses of 10-1000 ng/ml, where inhibin levels in the medium increased by 84.9-111.5% compared to the control (P < 0.01). FSH stimulated the inhibin secretion in the placental cells. EGF combined with FSH resulted in a greater response of placental cells in inhibin secretion. Addition of FSH (30 ng/ml) and EGF (0.1-1000 ng/ml) in the culture induced inhibin levels significantly higher than that of either FSH alone or EGF alone (P < 0.01). The effect of EGF on inhibin secretion was closely correlated with the seeding density of trophoblasts and the time course of culture. Obvious effect of EGF was found at the number of 1-2 x 10(6) cells per well and after 36-48 h of culture. Addition of 8-Br-cAMP, cholera toxin, or forskolin in the culture increased the inhibin levels more than 6-fold, 5-fold, and 2-fold, compared to the controls, respectively. When EGF combined with one of these agents was added in the culture, the inhibin in the medium increased to a level higher than those with the individual agents alone. EGF resulted in an increase in basal and cAMP induced human CG secretions in the trophoblasts in a similar manner as in the inhibin secretion. However, the effect of EGF on the proliferation of trophoblasts was not observed by measurements of the cell growth with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and DNA content in the cells with fluorescence spectrophotometry. Morphological study showed that EGF induced trophoblasts to differentiate and form syncytium. These data suggest that EGF stimulates inhibin secretion in human placental cells in vitro. EGF and its interaction with other hormones or growth factors may play an important role in the complicated hormonal regulation during human pregnancy.