Are oestrogen receptors and protein tyrosine kinases involved in phytoestrogen-modulated steroid secretion by porcine adrenocortical cells?

The phytoestrogens genistein and daidzein had been found to affect the function of some tissues via oestrogen receptors (ER). In addition, genistein, but not daidzein, is considered to be a protein tyrosine kinase (PTK) inhibitor. Thus, the involvement of oestrogen receptors and PTK in phytoestrogen action on adrenocortical porcine steroidogenesis was examined in this study. The aims of the experiment were to test the effects of (i) ICI 182, 780 (ICI), an ER antagonist, on genistein- and daidzein-modulated cortisol and androstenedione (A4) secretion by adrenocortical cells isolated during the luteal and follicular phases of the porcine oestrous cycle; (ii) tyrphostin AG 957 (TAG), a nonsteroidal PTK inhibitor, on cortisol and A4 secretion by the cells and (iii) the phase of the porcine oestrous cycle on the mechanism of phytoestrogen action. Adrenals were harvested during the luteal (n = 5 animals) and follicular (n = 5 animals) phases of the oestrous cycle from locally slaughtered crossbred gilts. The isolated adrenocortical cells were incubated for 8 h (37 °C, 95% air, 5% CO2) with genistein (5 or 10 μM) or daidzein (5 or 10 μM) in the presence or absence of ICI (0.5 μM) or TAG (5 or 10 μM). Genistein and daidzein inhibited cortisol secretion and stimulated A4 secretion by porcine adrenocortical cells harvested during both the luteal and follicular phases of the oestrous cycle. The ER antagonist ICI did not eliminate phytoestrogen-induced changes in steroidogenesis. In contrast to genistein, TAG reduced the secretion of A4 and did not affect cortisol secretion. There was no observable effect due to the phase of the cycle. It is suggested that the mechanism of genistein and daidzein action in the adrenocortical cells of pigs is independent of ER and PTK. It is possible that PTK are involved in A4 secretion by porcine adrenocortical cells.