| Abstract: | Control of the development and functions of avian oviduct is monitored by four classes of steroid hormones, including glucocorticoids. The effects of dexamethasone (DEX), a synthetic glucocorticoid, were studied via sequential treatments with estradiol benzoate, paying special attention to changes in estrogenic oviduct responses involving DNA synthesis and cell proliferation, ovalbumin accumulation and cell differentiation. DEX exerted an antagonistic effect upon estrogen stimulation when administered separately before or after estradiol benzoate (EB). Given before EB, DEX was more strongly antagonistic for DNA synthesis than when given simultaneously with EB. Administered after EB, DEX reversed EB-induced cell proliferation: the DNA content declined and the oviduct regressed. In the same way, protein and ovalbumin synthesis was inhibited and delayed by first intervention of DEX, and accelerated catabolism of ovalbumin and proteins was observed when DEX followed EB. DEX, which was ineffective alone, but synergistic on ovalbumin synthesis when given concomitantly with EB, prevented or dissipated the estrogenic effects, cell proliferation and secretory process when administered in sequential treatments. |
