Steroid binding to feather follicles in the chicken.

Steroid binding profiles in chicken feather follicles were studied in vitro. Progesterone and promegestone were bound specifically with high affinity (dissociation constant = 7.79 nmol/l in females and 2.0 nmol/l in males) and with low capacity to the high-speed supernatant fraction (cytosol) of homogenized feather follicles. The number of progestin-binding sites was significantly (P less than 0.01) higher in females than in males (1.35 +/- 0.07 (mean +/- S.D.) vs 0.605 +/- 0.15 pmol/mg protein). Significant cross-competition was observed between progestins and glucocorticoids for the binding sites. The heat-activated progestin-receptor complexes bound specifically to DNA-cellulose in vitro. The DNA-cellulose binding was 36.6% of the total specific binding. The presence of progestin-binding sites in the feather follicles implies a direct action of progesterone in this structure, which may be an important factor in the regulation of moulting. The lack of oestrogen binding to the cytosol prepared from the feather follicles suggests different regulation of progestin receptors in different target organs.