Effects of progesterone and tamoxifen on glucocorticosteroid-induced egg-white protein synthesis in the chick oviduct.
A single injection of either natural (cortisol, corticosterone) or synthetic [dexamethasone (DEX), triamcinolone acetonide] glucocorticosteroids to estradiol-primed, withdrawn chicks, resulted in a dose-dependent increase in the relative rates of ovalbumin and conalbumin synthesis. The simultaneous injection of equal doses of DEX and progesterone resulted in an additive effect on the relative rate of ovalbumin synthesis at all doses tested (range: 0.05-15 mg/chick), even when the induction of ovalbumin synthesis was maximal at 6 h, for either hormone injected alone. Moreover, the simultaneous injection of DEX and progesterone yielded an additive effect on the relative rates of ovalbumin and conalbumin gene transcription. The nonsteroidal antiestrogen tamoxifen does not increase ovalbumin synthesis and only slightly increases conalbumin synthesis. The simultaneous injection of tamoxifen and DEX potentiated the effect of DEX on the relative rates of ovalbumin and conalbumin synthesis, and amplified the DEX-induced increase in the relative rates of ovalbumin and conalbumin gene transcription. These results were supported by morphological studies carried out after 4 days of stimulation, which showed an increased accumulation of secretory granules in the magnum cells of the oviducts of chickens treated by tamoxifen plus DEX, as compared to that observed in chickens injected with DEX alone. In conclusion, these results suggest that glucocorticosteroids likely act through a mechanism distinct from that of sex steroids, and may modulate the effects of the latter on egg-white protein synthesis.