Desensitization of the chick oviduct to estrogen: mediation at different levels of gene expression.

We have investigated the effects of changing the dosage or kind of estrogen administered to immature chicks on the synthesis of two egg white proteins, ovalbumin and conalbumin, and the accumulation of their mRNAs. The results suggest that the oviduct can become desensitized to estrogen. Ovalbumin accounted for 25% of oviduct protein synthesis in chicks treated with low dose of diethylstilbestrol (DES; 0.5 mg/day) for 14 days. Within several days after the dosage of estrogen had been increased 10-fold, ovalbumin synthesis fell to undetectable levels. The synthesis of conalbumin also became undetectable when the dosage of estrogen was increased. Throughout the above experiment both ovalbumin and conalbumin mRNA activity, as measured by cell-free translation, remained elevated. This implies that expression of the ovalbumin and conalbumin genes may be regulated at the level of translation. In a separate experiment, ovalbumin and conalbumin synthesis also decreased when chicks primed with DES pellets were given an increased dosage of estrogen. Ovalbumin synthesis fluctuated, but overall decreased from 25% of oviduct protein synthesis after priming with DES pellets to 16% of oviduct protein synthesis after 7-12 days of injections of estradiol benzoate (1 mg/day). At the same time, conalbumin synthesis decreased from 10% to 6% of oviduct protein synthesis. In contrast with the previous results, changes in ovalbumin and conalbumin mRNA activity paralleled changes in ovalbumin and conalbumin synthesis. Thus, not only can the oviduct become desensitized to estrogen, desensitization can be mediated at different levels of gene expression.