Androgen receptor in the Harderian gland of Rana esculenta.

An androgen receptor has been identified in the cytosolic and nuclear extracts of the Harderian gland of the frog, Rana esculenta. A single class of high-affinity binding sites was found: Kd = 1.9 +/- 1.3 (S.D.) nmol/l (n = 26) for the cytosolic extract and Kd = 0.9 +/- 0.8 nmol/l (n = 15) for the nuclear extract. The presence of binding activity in both nuclear and cytosolic extracts and the low rate of ligand-receptor dissociation are characteristics that distinguish this receptor from a steroid-binding protein. The Kd did not show any sex difference and did not exhibit any secretory activity-related change. Binding in both cytosolic and nuclear extracts was specific for androgens (testosterone = 5 alpha-dihydrotestosterone); oestradiol-17 beta showed a 30% cross-reaction; moreover, specific binding of [3H]oestradiol-17 beta was not detectable. The binding capacity of the Harderian gland increased progressively in both fractions from October to December, reaching a peak in May, and decreased suddenly during July to August. The lack of any morphological sex-related difference in the Harderian gland of the green frog might be accounted for by the high amount of circulating androgens as well as a similar concentration of androgen receptor in both sexes.