To investigate why androgens are inactive alone, but act synergistically with estrogen to stimulate the chick oviduct, we examined the effects of estradiol on cytoplasmic testosterone receptor levels in the oviduct magna of White Leghorn chicks. Cytosol obtained from magna of 5-day-old chicks bound low levels of [3H]-testosterone (0.58 pmol/g of magnum). Seven days of estrogen treatment caused a 10-fold increase in the number of these binding sites. These sites decreased during estrogen withdrawal to levels similar to those found in the untreated chick. [3H]Testosterone binding again increased within 2 days after the administration of estrogen to withdrawn chicks. When administered alone to the estrogen-pretreated chick, testosterone, and, to a greater extent, dihydrotestosterone, were effective in stimulating magnum growth and maintaining ovalbumin mRNA levels as long as testosterone receptor levels remained elevated. These effects were not blocked by the concurrent administration of the anti-estrogen tamoxifen. Thus, androgen stimulation of the magnum was not dependent on the effects of low levels of estrogen remaining in estrogen-pretreated chicks. These results suggest that estrogen treatment is required for the induction and maintenance of the androgen cytoplasmic receptor and that the ability of androgens to modulate magnum growth and ovalbumin mRNA levels correlates with the concentration of this receptor. Inadequate levels of androgen receptor in untreated chicks or chicks, withdrawn from estrogen treatment for a period of weeks may be one factor explaining why testosterone and dihydrotestosterone alone do not stimulate the oviducts of these chicks.
|Original language||English (US)|
|Number of pages||7|
|Journal||Journal of Biological Chemistry|
|State||Published - 1979|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology